No-one could possibly have predicted that

Well, no-one could possibly have predicted that: Secondary school pupils 'not eating enough' according to the BBC headline. No, it's not an article about child poverty and malnutrition.

It turns out that...

For example, in 2004 43% of pupils had chips with their lunch compared to just 7% in 2011.

And almost all schools have ditched the sale of chocolate, sweets and crisps.

...if you remove the provision of food which is both tasty and provides lots of energy...

School Food Trust research suggests pupils get a quarter of the recommended daily intake from lunch, rather than the third that is advised.

[...]

"Despite huge improvements to what's on the menu, teenagers are still not choosing food combinations that will give them enough energy and nutrients to stay alert all afternoon."

...the people eating that food will be short on energy.

Apparently...

[the research] found significant improvements in the nutritional value of meals offered by secondary schools and healthier choices made by pupils.

It may well be true that the vitamins and other nutrients are
better provided than they were a decade ago. But as regards basic
energy, complaining that students aren't getting enough when there's
been a near-ban on the foods best at providing energy is absurd.

But then, this is a society where some "energy drinks" are actively
marketed as "low calorie"¹, so perhaps it shouldn't be all that
surprising that nutritionists are acting baffled at the reduction of
calorie content leading to a reduction in energy.

Footnote

¹ Because the way that calorie content of food is
calculated bears very little resemblance to most human's metabolic
processes², I can believe that it's very possible to
produce an energy drink which metabolises well but doesn't test high
in calories.

² Essentially: set fire to the food, see how much energy
this releases, then apply some 19th century adjustment factors to
vaguely account for composition. Modern
measurements skip the "set fire to the food" step and just
calculate based on broad composition approximately how much energy
would be released if one did set fire to it, but the underlying
principle is the same. People with furnace-based instead of
chemically-based digestive systems will probably get reasonably
accurate results from this.

More research on weight

DeeLeigh at Big Fat Blog reports on a Canadian study on weight and health in Manitoba. Full report (PDF).

A few interesting points

Mortality rates

The results - not surprisingly, by now - confirm the previous US, German and Canadian population studies. There is no statistically significant correlation between mortality and BMI - a person with a BMI of 19 and a person with a BMI over 40 have virtually identical chances of dying in any year. (Chapter 6)

There does seem to be some difference in causes of death - respiratory conditions are less common causes of death in "obese" people, and endocrine and metabolic conditions are more common - but as the German study pointed out - that just means we have a better idea of what statistically kills fat people. It doesn't make thin people any less dead.

Health service usage

The study also includes a very interesting look at health service usage by BMI in Chapter 5. Fat people do use more health services than thin people - to a statistically significant degree for some but not all services - but generally not by a very large margin. For instance, for visiting GPs, were the campaigns to get men to visit the doctor to succeed, bringing male GP visit rates up to the same as female GP visit rates, this would increase visits considerably more than if everyone visited the GP as often as a government-approved weight person of their gender.

Comments on the Big Fat Blog piece point out some reasons why correlation may well not be direct causation here - misdiagnosis of fat people necessitating repeat visits and weight gain caused as a side effect of medical treatment - and the German study also notes underdiagnosis in thin people of conditions popularly associated with obesity as another possibility.

The study doesn't cover health care costs directly - but they did do a brief literature review. Emphasis mine.

Studies of health care costs (not analysed in this report) show significant positive associations with BMI level (Andreyeva et al., 2004; Borg et al., 2005; Raebel et al., 2004; Thompson et al., 2001). This is consistent with the higher use of some healthcare services as shown in this report, though the differences appeared to be higher in those studies than results from this study would suggest. Some of this may be due to differences in the context and costs of healthcare, as most of these studies were done in the United States.

Or, paraphrased, if your health system is massively inefficient, expensive to use, and encourages people to only seek treatment in emergencies, you might well have very distorted costs. That doesn't mean that countries with more sensible health provision will have comparable costs.

Arbitrariness

Unlike many previous studies, this one recognises the arbitrariness of the BMI measures. After describing the World Health Organisation categories:

These categories were created by examining relationships between BMI, mortality, and morbidity. However, the cutoffs remain somewhat arbitrary and have changed over time: a BMI of 27 used to separate the low risk from the high risk categories [...]. Furthermore, these groupings may not be equally useful for older adults [...] or different ethnic groups, including Aboriginal peoples [...]. Therefore, analyses in this study used continuous BMI values whenever possible, with summarized data for the standard groups shown above as well.

I've mentioned the "step change" attitude that public health seems to take - it's good to see a study that explicitly takes the opposite approach, and doesn't take the WHO-set boundaries as definitionally accurate.

They also acknowledge many problems with BMI as a measure of weight categories (including assumptions of white European as default) - but note that they need to use something and

[...] it is the only measure available in existing data sources that covers a large and representative sample of the population (excluding residents of First Nations)

Changes over time

There are a couple of graphs in Chapter 2 noting that weight distributions have been basically static since 2000 in Canada (very similar to the situation in the UK). One of the things they note is that "overweight" is more common in men than women.

I suspect that a partial explanation for this may be due to flaws in the BMI measurement. BMI is based on a ratio of weight and height². But that's not a ratio found in nature¹ - scaling something up generally involves a ratio of weight to height^2.5, because of the way circulatory and nervous systems work at small scales.

So the simplification - which makes BMI possible to calculate without a scientific calculator or a log table - means that for people of the same build, BMI will increase with height.

Men tend to be taller than women, so will tend to have higher BMIs for the same build. (Also, there's not actually any reason, given that men and women have statistically different anatomies, that the BMI distributions shouldn't be different)

Afterthoughts

Studies like this leave governmental "obesity" strategy not as "correlation equals causation" but as "lack of correlation equals causation". There's no evidence that heavier weight harms life expectancy (though it may have some statistical effects on cause of death), and the effect on health care costs is likely to be trivial. It will be interesting to see if the Manitoba government, which commissioned this study, changes policy as a result.

Unfortunately the popular belief that "obesity" is both morally disgusting and voluntary² means that research into "how obesity is bad" gets far more attention and support than research into "is obesity actually bad for health?"

Footnote

¹ If you can view images, there's an unintentional "uncanny valley" effect in these images, where simple rescaling of the image of a person gives a slightly unusual effect. The relative sizes of body parts aren't supposed to be identical at each size, so it gives a strange effect.

² Even aside from the studies suggesting that weight and build are to a large part genetic, and that the "diet and exercise" mantra is so oversimplfied it's almost useless, this ignores the concept of constrained choices and so also contains a lot of classism, disablism, and other forms of discrimination.

Government-mandated weight. The inevitable consequence.

[trigger warning]

Unfortunately, I'm not at all surprised that this has happened. A UK Council is taking steps to have four of a family's seven children forcibly adopted (or fostered without contact).

Why? Because the children are fat, and have continued being fat against the local government's demands. Clearly the solution is to take them away from their parents - and perhaps away from each other, too - in the hope that the massive added stress will cause weight loss.

According to all the press reports, the family have "faced no accusations of deliberate abuse or cruelty". Their solicitor has previously stated that "obesity was the main reason for the children being taken from their parents".

The rather flawed research on "obesity" is a contributing cause, but this goes way beyond that. I'm unimpressed with the government's research on "obesity" in children. But, even if that research is accepted at face value, the only detectable effects of "obesity" in children are "low self-esteem and behavioural problems" and a greater chance of being "obese" in later life.

On the basis of that research - even accepting that research as high quality and accurate, which I don't - there is absolutely no cause for intervention in this case. Either:

1. Weight is largely not under a person's control. In this case, adoption won't change their weight. But it probably will harm their psychological state, especially since there's no reason to do it. Despite this stance being supported by the scientific literature, "everyone knows" means that more likely the council believe option 2...
2. Weight is entirely under a person's control. In this case, the effects of being heavy at their age are comparable to the effects of being adopted. There being no evidence of abuse or cruelty, the only effects are psychological - which must be compared with the psychological harm of adoption, including the effects on their older siblings. The children, when they get to adulthood, can then "choose to be thin" and suffer no long-term effects.

In either case, there's no reason to forcibly remove them from their family. Which should be obvious.

The only case where it isn't obvious is where you believe that "obesity" is basically an evil zombie cult. Fat people will exist near you and brainwash you into being fat. It's therefore imperative to get those children who could be un-brainwashed away from their family as soon as possible. Accepting that premise, Dundee Council's actions seem reasonable.

It's also not impossible that the Council's actions have been completely misreported. With multiple news entries several years apart, a verifiable trail in public record for at least some of the events, and several different news organisations covering this in different ways, though, that seems less likely. The Council hasn't denied any of it - merely issued a vague statement that "The council always acts in the best interests of children, with their welfare and safety in mind." which seems to be the well-known PR tactic of "lying outrageously" rather than a severely misreported case.

Big Fat Blog has contact details for four senior Council officers. I've sent them the following message.

Dear Sirs,

The recent news that Dundee Council is planning to place four children from a family of seven to either be adopted or fostered without contact, for the sole reason that they are heavier than the Council approves of, and in the absence of any deliberate abuse or cruelty by their parents, are, if accurate, extremely disturbing.

I hope that if the press reports are accurate you will be reconsidering this decision and the policies which led to it immediately, as it seems to me to be a strong infringement of the family's rights, and not in the interests of any of their seven children.

I realise that you are unable to comment on the details of any individual case for the family's privacy, and so therefore I am confining my questions to general Council policy. If the reporting is inaccurate, then your policies should provide sufficient evidence of this without the need to discuss this specific case.

1) Under what circumstances, if any, does the Council take the weight of a parent or child into account when deciding what interventions are necessary?

2) Under what circumstances, if any, would the Council require an individual to alter their weight?

3) If there are any circumstances as described in my first two questions, could you explain the reasoning behind these policies, and provide me with any research used in developing these policies.

Thank you

Since I don't live anywhere near Dundee, which is itself in a different legal and administrative jurisdiction to my own, I doubt I'll get a reply.

The overtallness epidemic

[trigger warning: body issues]

Researchers have announced that (BBC) being overtall gives an increased risk of cancer.

I haven't looked at the study itself, so I can't comment on whether it was well-conducted or not. I'm just interested in how the reporting has gone, so I'll assume it was well designed.

Essentially the study has found that an increase in height in women from around 150cm to around 170cm was associated with an increase in the cancer rate from 0.75% a year to 1% a year. Not a large effect for individuals, but certainly a noticeable one at the population level.

They also carried out a meta-study that suggested that a similar effect existed in men, though the BBC article goes into less detail about this.

There's a suggestion that this effect is in part behind the rise in cancer prevalence, since average height has risen by about 1cm every decade in Europe.

Cue panic and press articles about how the so-called "overtallness" epidemic is ruining our health, and we're all going to die if we don't wear heavy shoulder pads to shrink ourselves back down to 19th Century levels, all illustrated with photos of headless tall people.

No? My mistake.

The BBC article is actually calm and measured on this topic. It points out that there's no known mechanism by which overtallness could affect cancer prevalence, though a couple of theories are suggested. It doesn't blame tall people for bringing it upon themselves or suggest that they need to do more to reduce their height¹. Nor does it ignore the structural issues that make it hard for people to avoid being tall, pointing to better childhood nutrition and fewer diseases as reasons for overtallness.

One of the theories even suggests that overtallness doesn't cause cancer at all, but is merely a marker for underlying conditions that cause both overtallness and cancer. Correlation is not causation, after all.

If every medical research sub-discipline was so cautious about claiming causative relationships between health conditions and physical attributes, and similarly restrained about suggesting drastic individual measures to change the physical attributes, then we might have considerably better public health policy.

Footnote

¹ As I've said before (almost), there is no known safe way to permanently reduce height, though there are several methods which will appear to give noticeable effects if the follow-up period of the study is - no pun intended - too short, There are also some surgical methods that appear somewhat more effective but have extremely dubious safety records and large side effects.

Study shows researchers ignore structural issues

[trigger warning]

The BBC has yet another badly-researched story about "obesity". I'll skip over the unmentioned assumption that "obesity" is such a bad thing it needs to be prevented at all costs, and move on to places where the article fails even in its own terms.

Firstly, the article talks about how average calorie intake has increased significantly in the US since the 1970s. Naturally, because "obesity" is a personal problem with no structural issues whatsoever, the article completely omits that since the 1970s the USA's problems with perverse food-production subsdisies, "food deserts" and so on, in many places it's difficult or impossible to get foods other than the energy-dense ones, and more expensive even when they are available.

This is also something that does not really generalise to the majority of the UK, or other Western European countries, despite the claim in the article that "many of the factors causing the obesity epidemic there are mirrored in the UK".

The recommendations of the researchers - police what people individually eat, rather than making it easier for them to get nutritious food cheaply - are equally predictable.

Secondly, the article in a box-out includes a note that:

The recommended daily calorie intake is 2,000 for women, and 2,500 for men (NHS Choices)

If we assume that there are roughly equal numbers of men and women, and gender is the only factor that affects energy needs, metabolic rates, digestion efficiency, and so on - but does so with 100% predictive power (which is ridiculous, but is what the recommendation needs to be assumed) then that gives an average recommendation of 2,250 calories daily for each person.

Compare that with the figures from the article on US average - the article doesn't specify if it's mean or median - calorie intake:

• 1977-8: 1,803 calories
• 1994ish (implied): 2,145 calories
• 2003-6: 2,374 calories

So, comparing with the "recommended" average, we can see that it's only in the last decade or so that US residents have stopped being (on average) underfed.

The average hides a lot of rich/poor disparity, of course, and a lot of people in the US are still malnourished - my point is that even in terms of pretending these averages mean anything at all, the conclusion isn't the one that the rest of the article implies.

Of course, this is fairly typical of "anti-obesity" research and campaigning: set an unjustified target for calorie intake - and then claim it's bad when people get anywhere near it. "Pro-malnutrition" might be a better term for them: perhaps if they didn't have the privilege not to remember the effects of widespread malnutrition themselves, they'd think more carefully about what they were saying.

Or it might be that your major underlying assumption is rubbish

[trigger warning]

Another piece of terrible BBC reporting (complete with stock "headless fatty" photo), this time about life expectancy and the "obesity epidemic".

The lead paragraph is:

Life expectancy in the UK is on the rise, along with the rest of Europe, despite fears over the impact of obesity, a population expert has said.

In summary: life expectancy has been rising in the UK, mainly because of better treatment for heart conditions. This is a surprise, because as reading the news makes clear, everyone is becoming "obese" and should be dead already.

It can't at all be because - as major population studies in Canada, Germany and the USA have consistently shown - there is no statistically significant link between BMI (the measure of "obesity") and life expectancy.

We are yet to see the impact of a generation of people who have been obese from childhood through to adulthood. We can't predict how that will affect life expectancy figures in the future.

While more individuals nowadays are likely to be sufficiently far above the government-mandated weight that they count as "obese" for most of their lives (and especially now that the government - through the time-honoured technique of "making it up" - is defining more and more children as "overweight"), there are plenty of people who have been "obese" for all their lives, who were in those major studies, and who didn't die at any greater rates than anyone else.

But this argument¹ will keep them going on the "fat will kill you" track for a few decades.

At some point historians of medicine are going to look back and show how researchers managed to completely ignore major population studies saying "no effect" in favour of studies that don't get beyond correlation is causation, because they were so convinced of the truth of their main hypothesis that they just ignored evidence against it.

Until then, more terrible public policy and reporting, and more encouraging of hatred against fat people.

Footnote

¹ It occurs to me that this resembles the backstop argument for people when presented with unbeatable evidence of (e.g.) gender or racial inequality: "that is due to discrimination 30 years ago the after-effects of which haven't worked their way out of the system yet; in another 30 years it'll have gone". It's an argument that never gets old.

Harming fat people: why the government thinks it's okay.

After asking for some more details about the research behind the National Child Measurement Programme (NCMP), I got back some research papers.

Here's the papers I got. Full-text availability is variable.

1. Parents often do not recognize overweight in their child, regardless of their socio-demographic background (full text free)
2. Telling Parents Their Child's Weight Status: Psychological Impact of a Weight-Screening Program (full text free)
3. Recognition and management of childhood overweight and obesity by clinicians (full text requires subscription)
4. Can we recognise obesity clinically? (full text requires subscription)
5. Health consequences of obesity (full text requires subscription)

The second paper essentially describes the pilot study of the NCMP, and is an interesting read. One of the points made in the abstract, of course, is that "However, a minority of participants found it distressing, which highlights the importance of managing the process sensitively, particularly for families with overweight children.", and it's fairly clear from the news reports that the process has not been managed sensitively.

The first, third and fourth papers are all various ways of saying "Oh no! Not everyone is panicking enough about the obesity crisis! Even some doctors are relaxed!".

The fifth paper is the only one that attempts to show that "childhood obesity" is actually a problem - the other four proceed from the assumption that it is - and it's not a good paper (by which I mean it meets the internal standards of the field perfectly, but those standards are so bad that the paper is still terrible).

It shows a lot of correlation, but doesn't then go on to even consider the question of causation. The best example of this is probably the first area it looks at - psychological problems.

[...] We can conclude that obese children are more likely to experience psychological or psychiatric problems than non-obese children, that girls are at greater risk than boys, and that risk of psychological morbidity increases with age. Low self-esteem and behavioural problems were particularly commonly associated with obesity. [...]

Further on, in a section on long-term socio-economic effects of childhood weight:

[...] that obesity in adolescence/young adulthood has adverse effects on social and economic outcomes in young adulthood [...] For example, British girls born in 1958 who had BMI >90th centile when studied at age 16 had significantly lower income than girls with BMI <90th centile (by 7% on average) at age 23 [...]

Well, there's a surprise. It turns out that bullying and harassment, exacerbated in girls by the intersectionality with gender of appearance policing, and relentless social messages about the inferiority of fat people, will give fat people low self-esteem, with increasing likelihood as they get older and so live through and internalise more of this. When they get to adulthood, widespread discrimination in society then creates a noticeable pay gap.

Their solution is not to try to end this psychological assault but to reinforce it by blaming the victims for not being thin enough.

Given that they've entirely missed the obvious here, I'm not convinced that the claimed causation of other health conditions by "obesity" really holds either, especially since they admit that the evidence they review has weaknesses, and that the psychological impact is "likely to be the most widespread" consequence in childhood.

So, that's the quality of the evidence that the government is using. It's either terrible, or relies on assumptions for which the evidence is terrible. There doesn't seem a lot of point in writing back to point this out, though.

What happened next.

A few notes on what's happening now:

[trigger warnings]

• I got a reply to the letter I sent about the National Child Measurement Programme letters. No surprises: the government will keep doing what it has been doing, whether it makes sense or not. I've followed up to ask for more details of the research they're using to justify their decisions.
• A YouGov poll asks about opinions on rape defendant anonymity. A majority are in favour (considerably fewer women than men are in favour) but without a second question about how they feel for anonymity for non-rape defendants it's hard to tell why this is. The question wording really doesn't make clear the limited extent of anonymity (that it's only limited reporting restrictions, not that it wouldn't actually make any difference), which also makes things hard to tell.
• From PinkNews, the BBC trust thinks that a non-apology is sufficient for its posting of the question "Should homosexuals face execution?".
• When looking at the mass of exceptions to the Equality Act, I somehow forgot to look through the Schedules (many of which are titled "Exceptions", which should have been a big hint). There are a whole mass of further unhelpful exceptions here, and Zoe Brain and Helen G have highlighted several relating to gender reassignment.

Meanwhile, Jake Berry MP (Conservative, Rossendale & Darwen) asks if Parliament can get a cat. It will be investigated, apparently.

Insulting patients improves health, minister suggests

So, the BBC is reporting (with stock photo of "headless fatty", of course) that Anne Milton MP (Conservative, Guildford), the Parliamentary Under Secretary of State for Public Health, is suggesting that the NHS should use the term "fat" rather than "obese".

The article has the typical "opposing" views of "It's a harsher term, which is better" and "It can be considered offensive, which is hardly productive for doctor-patient relationships". A third view of "I consider it a neutral description of what I am, and would much prefer to be called fat than the negative overweight or obese." doesn't get a look into the article.

I'd had some hopes that the new government was going to drop some of the previous government's panic about the "obesity crisis". Sadly not (while the Minister was speaking in a personal capacity, her opinions presumably indicate something about how she thinks her department should be run). She talks about "personal responsibility", which completely ignores the social and especially class-based issues regarding access to good food or exercise, and the genetic diversity of body shapes.

As is usual for assumptions that are embedded so deep into the majority culture that they can barely be spotted, this makes absolutely no sense with even cursory thought. The Minister's contention is that people will take more "personal responsibility" for their weight if they are told about it in terms they find insulting.

Let's falsely assume that:

• All patients will in fact find "fat" more insulting than "overweight" and "obese".
• There is a general health benefit to be gained from weight loss. While some health conditions are more common in heavier people some are more common in lighter people, and the overall effect on life expectancy is basically zero. Some people might benefit from losing weight. Other people of the same weight might not.
• There is a way to cause long-term weight loss that doesn't have side effects worse than the health benefits of weight loss to this person. In other words, there's a "personal responsibility" that people can usefully take in the first place.

Even with those assumptions the idea that intentionally insulting your patients makes it more likely that they will follow your advice (as opposed to avoiding doctors entirely, or for those with sufficient privilege and luck finding a doctor who was awake in the "bedside manner" classes) is absurd.

Doctors have been advised to call their mountain-climbing patients 'sky-heads' to try to encourage them to avoid the hobby.

Patients will find "sky head" more insulting than "mountain climber". Even though they've never heard the term before because I just made it up. Mountain climbing generally increases health risks, and most people can easily choose not to do it. Nevertheless, no-one's going to suggest this approach.

Even for other cases where slurs previously existed related to a medical condition (plenty of disablist slurs to choose from here) or health-risk-increasing activity (lots of insulting terms for people addicted to drugs, for instance) it's not usual for ministers to hold up doctors who use them to their patients' faces as examples of best practice, as if there's some sort of debate to be had over whether it's a good idea.

(Ministers have other more socially acceptable ways to harm disabled people, drug users, and so on, which they'll use instead)

Yet another demonstration of how not only the "fat as super-dangerous" narrative is embedded, but also how the "fat-shaming is good" narrative is embedded.

Writing to the government

Some letters I've sent recently regarding recent issues. Specifically:

• Via Goriler of 3B, a letter asking that funding for a rape crisis centre not be cut. Please, if you have time, send your own as well, especially if you live in or near London.
• A letter to the Health Minister asking that they stop the letters accusing children of being too heavy.
• A letter to the Equalities Office to see if they have any idea what these exceptions are for.

Letters below.

[trigger warning]

As usual, please feel free to use these for inspiration for your own letters, though remember that letters in your own words are more powerful than copies of other letters, if you have the time and energy to do so.

Regarding RASASC

I sent this by email to mike.fisher@croydon.gov.uk.

Dear Mr Fisher,

You have recently announced that the funding for RASASC, the Croydon Rape Crisis Centre, will be cut by 27,000 pounds a year. This is a significant amount for a rape crisis centre, and it is likely to lead to the centre being unable to support hundreds of rape victims a year.

As the only rape crisis centre for the London area, the service it provides to victims is invaluable, and the effects of reducing its funding will spread well outside your own Council's boundaries. By running a helpline, supporting survivors of rape through counselling and through legal assistance at trials, it not only provides a vital public service, but provides a highly cost-effective way for your Council to support victims of crime.

The government have promised to improve the funding provided centrally for rape crisis centres, but it is not clear when - or even if - this promise will be fulfilled. Until then, it is necessary that others such as your Council play their part in keeping these services open. With thousands of rapes occurring in London each year, RASASC's ability to help additional victims is crucial.

Please restore RASASC's funding.

Yours sincerely,

[me]

Letters regarding children's weight

I sent this using the contact form on the Department of Health's website.

Dear Andrew Lansley MP, Health Secretary

I understand that you are looking for programmes run by the NHS and other health providers within your remit that could be reduced or eliminated without impacting the quality of front-line service.

I would like to suggest the sending of letters regarding the weight category of children, which is carried out as part of the National Child Measurement Programme. While the general aims of that programme are not in question, and the statistical data it gathers is perhaps worth much more to your department than the cost of gathering it, this particular application is not a good use of limited resources.

There have been a few reported cases - for example one last February reported at http://news.bbc.co.uk/1/hi/england/dorset/8523707.stm and one recently reported at http://news.bbc.co.uk/1/hi/england/leeds/10505584.stm - where letters telling parents that their child is overweight and warning of dire consequences, have been sent out to the parents of children who were physically active, eat healthily, and nevertheless happen to be marginally above the guidelines set out by the previous government for a person's required weight.

It is extremely likely that these cases are only the tip of the iceberg and there are many more letters being sent out in similar circumstances. The mechanism used to determine who gets the letters guarantees this.

Firstly, the letters are sent out based on Body Mass Index. This measure was developed as a way of providing a statistical estimate across a wide population of adults. It has never been appropriate to use as an individual measure, has not necessarily coped well with the increase in average height over the century since its introduction, fails to account for normal racial and sexual variations between individuals, and other forms of normal genetic variation, fails to distinguish between fat and muscle mass, and certainly was never intended to apply to children, whose shapes vary considerably and rapidly as they grow, especially in early puberty when the second set of measurements for the NCMP takes place.

Secondly, the children in regard of whom these letters are being sent are at a young and impresssionable age. It may have been the aim of the previous government in introducing these letters to encourage healthy eating and exercise habits to start early. In practice, of course, the effect can be quite the opposite - the child in the second article above refused to eat their meal when they discovered that - as is of course natural and desirable for growing children - their weight had increased since the NCMP measurement. This is something that could very easily turn into a serious eating disorder.

Thirdly, the science regarding weight is inexact. Multiple research studies - Orpana et al 2009 in Canada (doi:10.1038/oby.2009.191), Lenz et al 2009 in Germany (doi:10.3238/arztebl.2009.0641), or the NHANES studies in the USA (Flegal et al 2005) have shown that - at least in Western industrial societies - the mortality risk of people with a BMI in the 25-35 range is not statistically different to that of those in the current government-recommended 18-25 range (indeed, there may be a marginally lower risk for those in the so-called "overweight" 25-30 range). This is the research for adults, suggesting that the BMI guidelines set out by governments for them may not be correct. There is no similar research I know of for children - because, regardless of their weight, children very rarely die of weight-associated conditions other than eating disorders - but it seems very unlikely that the BMI guidelines set for them are correct either.

Fourthly, even if increased weight is correlated with an increase in risk for various health conditions, and even if that correlation is causative, which has generally not been shown, there remains no reliable long-term method for reducing weight in the long term. The few 5-year follow-up studies that have been done show that dieting is ineffective. Exercise certainly improves general health, but does not appear to cause weight loss. Early indications are that the surgeries currently being trialled have a greater chance of causing early death than any of the health conditions associated with above-average weight.

As you have gathered, I would like to see a general move away from the overemphasis of the crude BMI measure, and from the excessive conflation of weight and health carried out by previous governments, in general.

For now, however, I would appreciate it if the money used to produce and send these letters was reallocated into other more useful areas of your department's activities.

Yours sincerely,

[me]

Equality Act exceptions

And finally this one to the Equalities Office general enquiries address, to see what they know. I'll post up the response if I get one.

Dear Government Equalities Office,

I have a number of questions regarding the Equality Act 2010, that are not answered by the explanatory notes provided. Could you please provide me with the Goverment Equalities Office's current opinions on these matters.

The wording of Section 12 is not completely clear to me. While the application of legislation would ultimately be a matter for the courts, does the Government Equalities Office believe that this section would protect those people who identify as asexual (i.e. they are not sexually interested in people of any gender) as well as the bisexual, heterosexual and homosexual people that it more obviously protects?

In the areas of dual discrimination (Section 14), the protected characteristics of "marriage" and of "pregnancy" are excluded. Does this mean that an organisation that did not in general discriminate against people who were married, and did not in general discriminate against women, would still be allowed to discriminate against married women? If so, could you outline a situation where it would be desirable for this to be legal for an organisation to do?

The same characteristics are excluded from Section 26 (harassment). Could you outline a situation where the harassment (as defined in 26b) of a person or persons due to their marital status or pregnancy would be desirable, please?

In Sections 29.8, 33.6, 34.4, 35.4, 85.10, and 103.2, sexual orientation and relgious belief are excluded from the Section 26 harassment prohibition. For each of these situations, could you explain why it might be both necessary and desirable for a relevant organisation to carry out harassing behaviour against LGB people or people of a particular religion?

Section 85.10 also allows harassment on the grounds of gender identity. Again, please could you outline a situation where this is desirable?

Section 85.10 applies to the admission and treatment of primary and secondary pupils. Section 91, which covers the treatment of students in Further and Higher Education, does not contain a similar exception. Could you explain why it is not necessary for tertiary education providers to be allowed to harass LGBT applicants, given that this is apparently necessary for primary and secondary education providers?

Section 95 states that the chapter on General Qualifications Bodies does not apply to marriage or civil partnership. In what case would a qualifications body wish to do make use of this (for example by withdrawing qualifications from people when they were married) and why is it required?

With regard to the above questions, if the Government Equalities Office cannot provide an example of a situation in which a particular exception would be desirable, could you tell me if there are any current plans by the government to remove that exception.

Thank you

Yours faithfully

[me]

Computer says "lose weight, fatty"

[trigger warning]

The government continues its campaign to give every child their very own unhealthy relationship with food. The complaints about their plan only make the news - as in this case from February, or this one yesterday - when the child is fit and active and only just above the threshold at which the letters are triggered, but of course that doesn't mean that the letters actually make sense.

According to this earlier article [trigger warning: full of unchallenged fat hatred], letters are sent out to parents after measurements of 4-5 year old children and later of 10-11 year old children.

As a general principle, the National Child Measurement Programme is a good idea. Getting this sort of broad statistical information - and being able to compare it across years and decades - lets you track changes in the population and adjust accordingly (by making door frames taller as height increases, for instance)

This particular application of it, on the other hand, is absolutely terrible.

There are so many things wrong with the idea it's hard to know where to start, but for example:

1. BMI was designed as a population statistic measure. Since it's being used in a population statistics assessment, that's not unreasonable. However, it was never designed to be applied to individuals and has a number of extensively documented flaws for those who try.
2. Among those flaws is that it is designed for adult humans rather than the rapidly varying body shapes of children in early puberty or pre-puberty growth. Even if it was semi-meaningful for adults, it makes no sense for children at all.
3. Children tend to gain weight in early puberty anyway, which then often gets converted into energy to gain height later on. That's what's supposed to happen.
4. The letters seem to be sent out based on a point cut-off. So in the February article, we have:

   ... said that for a young girl, this meant she was 1% outside the healthy category and could be at risk of heart disease and cancer.

   There is not - obviously to anyone with any grasp of anatomy, medicine, or even basic statistics - any sudden step change in risks as you cross the arbitrary and suspiciously round number of the heavy edge of the government-mandated weight zone. (It's furthermore - as I've mentioned previously - not even clear that the risk gradient is upwards at this point). It's a hopelessly broken idea anyway, but applying this sort of step cut-off is absurd.
5. Equating health with weight and nothing else is as usual totally wrong, which is just obvious enough that the "but my child does ten different forms of regular exercise" stories make the news, but not quite obvious enough in UK culture that the rest of the logical conclusions get made.
6. As usual, it's going to completely ignore anyone who can't exercise for whatever reason, whether that is disability, a lack of local facilities, lack of time, or something else.
7. While there is a correlation in older adults between weight and some health conditions, it's not yet been shown that there the weight causes the conditions: for many it's more plausibly a symptom. Furthermore, of course, there's no known correlation between weight as a child and gaining these conditions in later life, certainly no correlation between weight as a young child and childhood incidence of these conditions, and people's body shapes and BMIs gradually change - sometimes quite significantly - over the years anyway.
8. The advice given, as the articles make clear, is going to be counter-productive. Exercise is all very well, but only for those people who can actually do it. Putting children on diets - or worse, permanent "weight-loss" surgery - will usually actively harm them, either through childhood malnutrition (which is strongly correlated with a bunch of nasty health conditions), or causing an eating disorder, or both).

I wonder if the coalition could be tempted into making an "efficiency saving" in the NHS and stopping sending out these letters. At about 1.8 million children in the relevant age bands, "most" of whom are surveyed and presumably receive a letter, that's potentially quite a bit of money saved.

Making a rough guess that the cost of sending the letter, not counting any costs that would have been incurred by the useful bits of the programme, is about £1 for the envelope, bulk postage rate, paper, printer ink, additional wear and tear on equipment, and staffing costs, that's around 1 million pounds a year that could be spent on either hospital equipment and staff, or on an effective and useful public health initiative.

The coalition so far hasn't said much on the "obesity epidemic" and neither party mentioned it in their manifestos. The Health Secretary rightly criticises the approach of Jamie Oliver, which seems to have been as counterproductive here as when he was temporarily exported to the USA. So perhaps there's a chance that this policy could be dropped.

A distorted image of science

[trigger warning for eating disorders]

The BBC, in its usual uncritical way, reports on a paper claiming that people's sense of proprioception is not great. Proprioception, if you haven't heard the term before, is the internal sense of position - you know where any limbs you have are in relation to the rest of your body, at what angle your head is to your shoulders, and so on, without having to look.

The paper itself (payment/subscription needed for full text) is really quite interesting. They tested how exact this sense of proprioception is by asking people to point to the fingertips and knuckles of one hand with the other hand while not being able to see it, and found that people tended to miss by a fair bit, estimating their hands to be shorter and wider than they really were.

I tested this briefly in an uncontrolled fashion with my own hands, and yes, this does seem to happen to at least some people.

So, the next time someone tells you that they know X like the back of their hand? Worry.

This is not an area I have much knowledge about, so if there are giant flaws in the research methodology, I don't stand much chance of finding them. There are none stunningly obvious to me as a scientific generalist, though some things that do stand out are:

• All of their experimental samples (for four variations of the study) have more women than men, some by a significant margin. If gender was significantly affecting the results they didn't mention it, but this suggests some other bias in how they recruited their samples which might be significant.
• They don't mention, but it seems likely by implication, that all of the sample had relatively average vision. Whether this effect also occurs in people who aren't able to use vision to supplement proprioception in most cases seems an important question.

The flaws, as usual, come in the interpretation for the press release and news articles, where, according to the BBC:

The brain naturally distorts body image - a finding which could explain eating disorders like anorexia, say experts.

[...]

Distorted perception may dominate in some people, leading to body image problems, a US journal reports.

Lead researcher Dr Matthew Longo said: "These findings may well be relevant to psychiatric conditions involving body image such as anorexia nervosa, as there may be a general bias towards perceiving the body to be wider than it is.

"Our results show dramatic distortions of hand shape, which were highly consistent across participants."

...and in come the wild extrapolations.

It is, I suppose, possible that the body image distortions of anorexia nervosa have the same basic cause as this one, and it would be entirely reasonable to do some follow-up studies in this direction.

But there's no evidence yet to justify Dr Longo's speculation that there's even a tendency to misperceive your own body width in the general¹ case, or that people with anorexia nervosa misguess where the edges of their body are more than people without.

The proprioception errors they report on are fairly clearly not "proprioception plus vision" errors, but anorexia nervosa is not generally a condition that only takes effect when not observing oneself visually, which is some evidence that they aren't the same effects.

The hand distortion seems to be fairly consistent across the sample and not related to any obvious social effects. Anorexia nervosa has been fairly strongly linked to social effects, and varies widely in severity across the population.

It's an interesting study with potentially interesting follow-ups, but both the news article and Dr Longo's quotes are assuming prior to doing the needed follow-up studies that the distorted body image of proprioception and the distorted body image of anorexia nervosa are distorted in the same way, or even involve the same meaning of "body image". As usual, the BBC seems to have largely uncritically reported and extended a press release.

Here's the original press release - there's one relevant quote at the end, in a press release that otherwise actually summarises the research very well:

“These findings may well be relevant to psychiatric conditions involving body image such as anorexia nervosa, as there may be a general bias towards perceiving the body to be wider than it is. Our healthy participants had a basically accurate visual image of their own body, but the brain’s model of the hand underlying position sense was highly distorted. This distorted perception could come to dominate in some people, leading to distortions of body image as well, such as in eating disorders,” said Dr Longo.

It's not as bad as some of the BBC's science reporting, but it's got all the same types of error - unjustified extrapolation, uncritical reprinting of press releases, not reading the actual paper, etc.

¹ They might also need to sharpen up their recruitment strategies to get a control group from a society where "thin is good / fat is bad" isn't the overwhelming social message.

Parents have more sense than BBC journalists, then

From the BBC, another reprint-the-press-release article, this time with the headline Parents 'more worried about murder than obesity' threat.

On the whole, this seems like a sensible balance. Murder may be rarer than "obesity" but the consequences are significantly more severe.

The findings, in a YouGov poll of 1,244 parents, contrast with data showing the risk of a child being killed by a stranger is a million to one.

The risk of severe health problems for children due to lack of exercise is one in three, figures have suggested.

"Figures have suggested". No mention of what figures, or how reliable, or anything. Also note the addition of the qualifier "by a stranger", which is necessary given that the risk of being killed - at any age - by someone one knows is considerably higher.

As mentioned before, research shows that - for Western industrialised populations at least - the death rate is not significantly correlated with weight (and in so far as it is, the government-mandated weight is correlated with a higher risk of death within a particular time period than heavier weights).

The article does talk more about "long-term health problems" than death as a consequence of obesity, but what's not mentioned is that the evidence that the correlation is causative is sparse. Indeed, for many "obesity-related" conditions, there is more evidence of the reverse - that weight gain is either a symptom of an underlying condition or caused by an underlying factor that also causes susceptibility to that condition.

That lack of evidence of causation is of course a serious problem for the government policies developed around this. It's much like the government, upon discovering that people with blonde hair were more likely to have a particular health condition, recommending hair dye - except that in this case some of the suggestions for hiding the symptom are actively harmful to health.

The article doesn't, at least, mention restrictive diets for children as a possible "solution", instead advocating more exercise and walking to school. The problems with "more exercise" and "walking to school" as a solution have been repeatedly said elsewhere, so to summarise:

• Not every child can exercise that much, because of disabilities, and/or a lack of suitable or sufficiently cheap places to exercise near where they live, and/or a lack of free time.
• Similarly, it's not practical for every child to walk to their primary school, due to the distance, or lack of time, or inaccessible routes.
• The effects of exercise on weight are not particularly clear in adults. I don't know if there have been useful studies specifically for children.

So that's the conclusions, but what about the data used to conclude them? Going back to the article, it's fairly clear that - despite YouGov being a reputable survey company - the questions that they were given to ask were clearly set with the aim of producing the press release in mind. From the BBC article.

But only one in 20 picked concerns about poor health in later life due to the child's levels of physical activity.

Here's the options for the question, which was "which of these do you fear most for your child?"

• They are injured or killed in a road traffic accident - 30%
• They are abducted or murdered - 30%
• Poor health in later life due to your child's current levels of physical activity - 5%
• None of these - 21%
• Don't know - 7%
• Prefer not to say - 7%

This is not a good question.

Note that the survey - unlike the press release and the article - doesn't qualify "abducted or murdered" with "by a stranger". Given how prevalent abusive relationships are, that makes the "million to one" statistic pretty much irrelevant. It's like asking someone whether they're scared of being bitten, and then laughing at them if they say "yes" on the grounds that hardly anyone is attacked by sharks.

The important thing to note is that the survey only gives those three options, plus a few standard "none" options. If the survey was repeated, but with a more substantial list of plausible fears (and perhaps some that the surveyors believed less plausible), then this would give a very different result. People tend to go more for options that they're prompted for, rather than "Other". Of the three options, especially as worded, the third is - regardless of relative risk - considerably less scary.

It wouldn't surprise me if they wrote most of this press release before the survey results were back, and just added the exact numbers later.

So, bad data collection, and then conclusions that aren't really supported by the data anyway, and then reprinted pretty much from the press release without any challenge. Exactly the "standards" I've come to expect from science reporting, in fact.

In 1950, crisp packets contained no crisps

According to the BBC, some researchers have analysed the size of the plates in depictions of the Last Supper between 1000AD and either the 1700s or 1900AD (the article gives both as dates for the most recent painting analysed).

This research is not, as might be expected, found in an interesting journal of art history, but in the International Journal of Obesity. I don't have access to the full text of the research, so I can't tell how good it is. However, the news article is not hopeful.

The Guardian article gives slightly more details, including the source they used to find the paintings (which are mostly Western European and Russian in origin, judging by the Amazon's index).

So, flaws in at least the reporting, and possibly the research too:

Firstly, the differences in style between eras of European painting are ignored. Pre-renaissance painting was largely symbolic, for instance, and the pursuit of a "realistic" style has varied considerably over the centuries. The Last Supper, as one of the major events of Christianity, has a lot of associated symbolism. That starts to make comparisons based on a simple head:plate ratio less valid (though not as invalid as they would be from a larger selection).

Neither of the researchers is an art historian by speciality (Reuters describes what they do specialise in), but without the full text I can't tell if they asked someone who was or not.

Secondly, the use of plates may have changed over that time. Was every plate depicted a plate of comparable function? Without the source material and a better knowledge of the technology I can't tell. There is a risk, though, of comparing side plates to main plates. Similarly, changes in numbers of courses may have had an effect - if the number of courses being eaten increases, the average plate size for a course will probably decrease, and vice versa.

Thirdly, the reporting seems to be linking this to "portion sizes are getting bigger so there's an obesity crisis!!!". Since the phrase "super-sized" appears in all three news articles, despite them otherwise being very different in wording, I'm guessing this was introduced either by the press release or by Brian Wansink.

The major problem with this is that the range 1000AD to 1900AD was not characterised by any sort of obesity crisis whatsoever. It was characterised by major famines, general malnutrition, and other problems related to lack of food (especially for people outside the nobility, and especially towards the start of the period).

As farming and storage technology improved, and as European nations invaded large parts of the rest of the world to bring increased prosperity at their expense, it probably is true that over those 900 years the amount of food available to Europeans generally increased. This may have had a general effect on the size of plates and the amount of food on them in artwork - that's entirely plausible.

The conclusion, however, that some people seem to be drawing, is entirely unfounded. From the BBC article:

Charlene Shoneye, an obesity dietician for the charity Weight Concern, said: "I'm really not surprised by these findings because the size of our plates and food portions has increased.

"Twenty years ago, for example, most crisps used to come in packs that were 20g. Now they are 30g, 50g or even 60g, and we are still eating the whole pack.

"This super-sizing has changed our perception of normal."

But she said it was not too late to reverse the trend and that individuals, society and the food industry should look to smaller portions.

So, this person is not surprised at a general increasing trend between 1000AD and 1900AD because of a separate trend between 1990AD and 2010AD¹? This is fairly typical of some of the "science" behind the "obesity epidemic", but not being able to tell the difference between a trend based on the slow eradication of malnutrition and a trend based on marketing decisions is not a good sign.

Widespread malnutrition probably would stop most people from being above the government-mandated weights, but it's not a great policy idea. The whole "obesity epidemic" panic, though, seems to be predicated on a "wasn't everyone healthier when they were borderline-malnourished" idea - with "so let's put them on diets to induce this state" the obvious conclusion.

It's a conclusion that can only be drawn when you have the privilege not to be able to personally or culturally² remember widespread and unavoidable malnutrition.

¹ Further on the crisps point - yes, the packs do vary in size (you can even get 100g and 150g packs of some brands), but the cost varies with the size. A 50g bag of crisps is more expensive than a 30g bag of crisps. The 30g bag of crisps is probably more expensive (after correcting for general crisp-related inflation) than the 20g bags were.

² There are people, and groups of people, of course, even within the Western European and Northern American countries currently worrying about the "obesity epidemic", who don't have enough food. Society and privilege make them sufficiently invisible to many "obesity researchers", though.

Unable to escape their initial assumptions

Via a comment at Shapely Prose (in a piece well worth reading itself) I was directed to BMI and Mortality: Results From a National Longitudinal Study of Canadian Adults (full text, for once, public!), yet another study of the correlation between BMI and lifespan, similar to the US and German studies previously mentioned.

It largely repeats the results of the previous studies: a BMI below 18.5 or above 35 is associated with a statistically significant (though small, especially for "above 35") increase in risk of death compared with a BMI in the 18.5-25 range, and BMIs between 25 and 30 are associated with a statistically significant (though again small) decrease in risk of death.

Let's take as read for now, because it's been covered many times before, that:

• most importantly, there is no moral value associated with healthiness or having a particular BMI anyway. While governments might understandably want a longer-lived and healthier population, because it makes their jobs easier, and while many individuals understandably might themselves like to live long and healthy lives if possible, that doesn't mean that there's any requirement on individuals to be healthy - it's often out of their control, and even when it is within their control, there may be other things they think are better uses of their time, energy and money;
• BMI as a usable statistical population measure does not make it a useful individual measure for a whole range of reasons;
• there is no known way to reliably effect a long-term change in weight;
• correlation is not causation: just because people with a particular BMI are more likely to die in a given time period doesn't mean that this is caused by being in that BMI range, nor does it imply that magically increasing or decreasing their weight would make them live any longer.

The way the paper is written is quite interesting, and indicates that the authors have a deep belief that fat is bad that they're trying to preserve in the face of the evidence.

Firstly, there's the way that they refer to the 18.5-25 BMI range. This may just be standard terminology for epidemiologists in Canada, but referring to it as the "acceptable" range is unusual. It's what "normal", it's more common name, means, of course, but it's unusual to see someone come right out and say it.

This is an important public health message, because while overweight may not be a risk factor for mortality, becoming overweight is a necessary step between being of acceptable weight and becoming obese.

This is key evidence of their assumptions. There's an initial assumption that being "obese" (categories 30-35 and 35+) is unhealthy. The relative risk of the 30-35 category is, within the bounds of statistical significance, exactly the same as the "acceptable" 18.5-25 category. The 25-30 category has less risk than either (though this is barely significant).

One could therefore equally phrase this in the opposite direction. Let's take a similar sentence with the same risk pattern to show just how absurd the conclusion is.

This is an important public health message, because while being hydrated may not be a risk factor for mortality, becoming hydrated is a necessary step between being acceptably dehydrated and dying of water poisoning.

The sentence only makes any sort of sense due to the power of "acceptable BMI" as a default, but even with that, it's still nonsensical: "we won't encourage behaviour that might be healthy, because if people do it too much, it's unhealthy again" (mind you, the same logic, if applied consistently, would also discourage attempts to lose weight, so maybe it's not all bad.)

Another bit that makes a similar lack of sense is this bit. As background, if you didn't read the entire paper yourself: they took people who reported their height and weight in 1994/5, and checked if they were still alive in 2006/7. They then used their 1994/5 BMI, among other factors, to determine the risk factors. This quote follows immediately on from the last one about public health:

Other analyses using the National Population Health Survey data demonstrated that almost a quarter of Canadians who had been overweight in 1994/1995 had become obese by 2002/2003 and Canadian adults within all BMI categories continue to gain weight.

They present this as a bad thing, of course, but of course they're not following through the logic enough. These people have gained weight relative to their starting weight, often by a sufficient margin to move them into a different category. They haven't died. This is not evidence that any of these are dangerous except for the prior assumption - which the data isn't supporting - that being "obese" is dangerous.

If the sample are generally gaining weight (and we'll assume, since it's a sample of adults, that most are not significantly changing height over the period of the study), that suggests that this effect is already accounted for in the relative risk. Looking at the age breakdown in Table 2 suggests this further: the relative risk associated with less than 18.5 BMI rises, and the relative risk associated with above 25 BMI generally falls, for the older part of the sample, which is what would be expected if gaining weight over time was common (though only one of these figures differs from the reference category by enough to be statistically significant).

It's worth noting, of course, from Table 1, that the people over 60 in Table 2 have a relative risk factor due to their age of between 10 and 100 compared with those under 60, which is not surprising, and would completely swamp any of the BMI risk factors - which as has already been said, are either barely significant or statistically insignificant - for any age band.

So we have a study that shows being "overweight" appears not to be harmful, and being "obese" largely appears not to be harmful, and a group of researchers trying to suggest other ways it might be harmful because they can't believe that the "acceptable" weight band could be anything other than the "best". It's a common pattern in weight-related research.

The power of the default and its assumptions are strong indeed, and so despite an increasing volume of studies showing that weight has virtually no effect on health, many of the major public health programs are trying to combat an illusory problem, with no effect other than to demonise a significant part of the population.

Another BMI vs life expectancy study

This meta-study from Germany by Lenz, Richter and Mühlhauser looks at the correlation between weight and death due to various conditions.

As is usual for these studies (the NHANES data from the USA, and a more recent Canadian study, for example), the result was that - on average - being "overweight" was correlated with fewer all-cause deaths than "normal weight" (though, like NHANES, not statistically significantly). Some individual causes were more common in lighter people, some were more common in heavier people. "obese" was not statistically significantly different from "normal weight" in some cases, and the effect was otherwise minor.

This quote from page 646 (the PDF is an extract and translation from a journal, so page 6 of the PDF file) is quite telling:

In addition, the medical literature primarily analyzes those diseases for which an effect through overweight or obesity is plausible to exist. Thus, there is a suspected investigational and publication bias for diseases that appear to be favored by overweight or obesity.

This assumption is supported by the results of the mortality analyses: all cause mortality is not increased in overweight individuals. This parameter is made up of disease-specific mortality risks for each disease. Many of the diseases analyzed here yield elevated risks. Accordingly, there must also be still unidentified diseases with a reduced risk.

In other words, people are looking, in great detail and with lots of funding, for diseases that might kill fat people, especially ones where they can think of a plausible reason that it might. Far fewer people are looking for diseases that might kill thin people. It's therefore not surprising that being fat appears more dangerous, but actually, it's just that we don't know what does (statistically) kill thin people.

There's a similar effect, which the paper also discusses, regarding non-fatal illnesses that more often affect fat people and more often affect thin people: again, illnesses primarily affecting fat people are well-documented and researched. No-one's entirely sure what illnesses thin people get, which will not help you if you're both thin and ill.

The paper doesn't discuss correlation versus causation for any of the diseases. To some extent in this context it doesn't matter whether the disease affects you because of your weight, or whether the disease and the weight are both connected to some underlying factor: either way, diseases primarily affecting thin people are underresearched - which leads to the assumption of thin=healthy, fat=unhealthy, and a whole mess of policies and public messages based on this clearly wrong assumption.

From page 647 (page 7 of the PDF)

There are also confounding factors the effect of which are plausible, but cannot be quantified. In the risk of developing diabetes these include undiagnosed cases that are more frequently discovered in overweight and obese persons (e44). It is suspected that greater attention is paid to diabetes in these groups.

In other words, diabetes may be detected more in heavier people because previous research has suggested that heavier people are more likely to have diabetes, which means that doctors are more likely to check fat people for diabetes, which means it's more likely to be discovered, which means future research can note the correlation.

Nice to know that our "biggest health challenge" may be based entirely on some extremely badly-done statistics and (unintentionally) selective research.