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Myths and presumptions about obesity

People who are perceived to be overweight according to the norms set by society have a tough time. We live in a media-saturated world in which thinness is not only treated as a desirable marker of good looks and good health, it is also seen as somehow virtuous and hence people who are above the norms in weight are seen as being somehow morally weak and lacking in will power to control how much they eat. This is despite the fact that it is not at all clear what a person’s optimum weight should be, how much it is affected by distribution and body shape and age, what causes some to be heavier than others, and even whether being overweight is as extremely unhealthy as it is sometimes made out to be.

A couple of years ago I wrote about this phenomenon and how some people are fighting back and “have rejected the idea that the word fat is some kind of slur requiring the use of euphemisms to soften it, and have embraced it and made it their own, the way that the gay community did with the word queer. They are fat and proud of it.”

Their position gains some support from a recent study that finds that there are a lot of misconceptions about obesity. Based on a survey of the research literature, the paper published in the New England Journal of Medicine highlights seven myths about obesity that are just not supported by the evidence.

Myth number 1: Small sustained changes in energy intake or expenditure will produce large, long-term weight changes.

Myth number 2: Setting realistic goals for weight loss is important, because otherwise patients will become frustrated and lose less weight.

Myth number 3: Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss.

Myth number 4: It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment.

Myth number 5: Physical-education classes, in their current form, play an important role in reducing or preventing childhood obesity.

Myth number 6: Breast-feeding is protective against obesity.

Myth number 7: A bout of sexual activity burns 100 to 300 kcal for each participant.

The authors also point to six presumptions that are widely held but are either not supported or are contradicted by the evidence.

Presumption number 1: Regularly eating (versus skipping) breakfast is protective against obesity.

Presumption number 2: Early childhood is the period in which we learn exercise and eating habits that influence our weight throughout life.

Presumption number 3: Eating more fruits and vegetables will result in weight loss or less weight gain, regardless of whether any other changes to one’s behavior or environment are made.

Presumption number 4: Weight cycling (i.e., yo-yo dieting) is associated with increased mortality.

Presumption number 5: Snacking contributes to weight gain and obesity.

Presumption number 6: The built environment, in terms of sidewalk and park availability, influences the incidence or prevalence of obesity.

So why are all these things so firmly believed despite the lack of solid evidence? The authors speculate:

Why do we think or claim we know things that we actually do not know? Numerous cognitive biases lead to an unintentional retention of erroneous beliefs. When media coverage about obesity is extensive, many people appear to believe some myths (e.g., rapid weight loss facilitates weight regain) simply because of repeated exposure to the claims. Cognitive dissonance may prevent us from abandoning ideas that are important to us, despite contradictory evidence (e.g., the idea that breast-feeding prevents obesity in children). Similarly, confirmation bias may prevent us from seeking data that might refute propositions we have already intuitively accepted as true because they seem obvious (e.g., the value of realistic weight-loss goals). Moreover, we may be swayed by persuasive yet fallacious arguments (Whately provides a classic catalogue) unless we are prepared to identify them as spurious.

A colleague of mine who is a faculty member in the nutrition department of the medical school argues that instead of focusing on permanent weight loss (which is hard to attain) it is far better to urge all people (not just those who are perceived as overweight) to aim for a healthier lifestyle in terms of what we eat and drink, and to lead more active lives with regular exercise. This is a much more attainable, not to mention enjoyable, goal to aim for and easier to attain than losing weight by adopting exotic or draconian diets, and results in much better health outcomes. In the process, some people may lose weight and others may not but that would be incidental.

He says that what we should not do is give overweight people a hard time. His reading of the relevant research suggests that it is usually a waste of time nagging people to lose weight. It is hard to do so and even harder to keep it off if you succeed. This leads to yo-yo weight fluctuations, resulting in feelings of failure, anger, and even depression. People who repeatedly try and fail to lose weight are often tempted to just say to hell with it and stop doing anything at all and give up on attempts at being healthy.

He says that what we should watch out for are our blood pressure and risk factors for stroke. Being overweight is one of the risk factors for Type II diabetes so it is not something to be taken lightly but it is one of many risk factors and we should not focus on it to the exclusion of others. It is health that is important, not weight.

The Daily Show back in 2010 had a clip on this topic and some of the overwrought rhetoric that surrounds discussions of weight in the US.

(This clip was aired on June 22 1, 2010. To get suggestions on how to view clips of The Daily Show and The Colbert Report outside the US, please see this earlier post.)


  1. unbound says

    “So why are all these things so firmly believed despite the lack of solid evidence?”

    To be honest, many family medicine doctors (perhaps most doctors in general) propagate these myths…especially the list of presumptions (I’ve personally heard 4 or 5 of them from my past doctors). Many family medicine doctors are too beholden to simple charts which leads to poor information as well.

    As an example, my daughter is ranked as slightly overweight via the BMI methodology. I get a chuckle when she interacts with a new doctor who starts to comment (based on the BMI) about my daughter’s activity and eating habits. When the doctor then looks at my daughter, then (and only then) realizes that the question was entirely stupid (my daughter is extremely athletic and one of the fastest players on the field for her sport in the entire state). My daughter probably has some genetic abnormality that makes her legs more muscular, thus showing a higher weight…but how many other people are painted as being lazy or over-eaters when they really may not be far off from their individual ideal?

  2. says

    There’s also a lot of pseudoscience. The BMI formula, for example, is just an approximation of Quetelet’s charts of ideal weights – because formulae are much more sciency. How did Quetelet get his chart of ideal weight? Simple: he asked his friends who he considered well-proportioned, “what do you weigh?” Quetelet’s charts were fleshed out – presumably, by filling in empty cells, by actuaries in the 1950s, and tweaked slightly. But, basically, generations of people have tormented themselves to try to comply with an ideal set by a 17th-century researcher’s circle of friends.

  3. Jared A says

    The BMI thing is so outrageous, and the fact that so many doctors take it seriously is silly. The more I learn about it the more meaningless it seems. It bases so much on height as if that is a good indicator of what your ideal weight is. As far as I can tell shorter legs aren’t much lighter than longer ones because they pack on as much muscle mass anyway. So you can have two people with the same size torso, same appearance with regards to musculature and fat deposits, but one has much shorter legs, and according to the BMI the taller person is average and the shorter person is obese.

  4. glodson says

    That’s something that is not mentioned enough. I’m a 6 foot tall man who weighs 190 pounds, I’m actually quite slender. The BMI says that I’m overweight. I am actually having fun with this now, putting in the height and weight of some athletes. All of them, overweight….

  5. Mano Singham says

    Athletic people are often found to be ‘overweight’, which should give us a clue that BMI should be taken with a huge grain of salt.

  6. Brandon says

    BMI is nearly useless, but it seems that it’s become something of a strawman at this point. Almost anyone that’s paying any attention at all is well aware that it’s not a useful measure of much of anything for individuals and isn’t even a great measurement for population level studies (although it has some uses there). I don’t think that trying to there’s any well informed people that are inclined to tell an individual that they’re unhealthy because of a single number, whether it’s BMI, standing heart rate, body fat percentage, or anything else.

    I absolutely agree with your colleague’s advocacy that we encourage people to exercise and improve their diet, then regard weight changes as a biproduct of other good things happening rather than as the primary focus. For quite a few people, healthy habits are associated with weight loss and/or body remodeling, which is nice, but it can’t be the only thing that someone’s shooting for.

  7. glodson says

    I swear, I spent about a half hour just putting in random athletes in. Hell, I even tried to fine tune it to find how tall I would need to be in order to not be overweight, and it was 6 foot 2 inches. I don’t know why that amused me so much.

    But I guess the reality is that it isn’t that funny. I can laugh it off because of my situation. It is junk science, and it is being used to evaluate the health of people. A doctor who told me that I was overweight would find himself losing a patient. However, that’s just a function of who I am and my place in this culture. Others would find this news devastating, and it could have real negative effects despite them being of healthy weight.

    In some ways, this is a problem apart from the obesity myths, and yet tangentially a part of it too.

  8. syd says

    Yet for most people with a high bmi it’s quite obvious that the problem ins not “too much muscles”. In my opinion such discussions are often just a convenient way of distracting from the real issue

  9. says

    A colleague of mine who is a faculty member in the nutrition department of the medical school argues that instead of focusing on permanent weight loss (which is hard to attain) it is far better to urge all people (not just those who are perceived as overweight) to aim for a healthier lifestyle in terms of what we eat and drink, and to lead more active lives with regular exercise

    Presumption number 5: Snacking contributes to weight gain and obesity.

    Presumption number 6: The built environment, in terms of sidewalk and park availability, influences the incidence or prevalence of obesity.

    These are not unrelated; whether or not the presumptions are strictly true in direct proportion, there is a strong correlation. Notably, although it is no t demonstrated to reduce obesity per se, the built environment heavily affects the extent to which people ‘ lead more active lives with regular exercise.’ Also, the rise in obesity rates coinciding with the dramatic increase in portion size and variety of highly processed, calorie dense, micronutrient poor snack foods, and relative reductions in price is most likely not coincidental. The solution there is to heavily alter the structure of our food supply (a large portion of the increase in ‘junk food’ availability has been massive subsidies for corn and soybeans), by removing subsidies for those crops and feeding it into a combination of capital subsidies for varied farms nearer to/in cities and increases in foodstamp budgets. Also, there needs to be a dramatic increase in the minimum wage(and shorter workdays/workweeks and more vacation, and a single payer healthcare system, and a guaranteed minimum income, while I’m dreaming); these combined should make better food more affordable and increase the relative price of junk foods. Once again, this will make it much easier for people to shape their eating habits.
    My point being, these lifestyle factors aren’t really choices for a lot of people because of the way that their environment shapes their lives and limits their options; we need to change these environments.

  10. filethirteen says

    I agree that BMI is broken. I also agree that it doesn’t help to give people a hard time about being overweight. That said, we do need to come up with some solution because it’s a huge problem that shouldn’t be minimised and society needs to find a way to deal with it. I don’t know exactly what the solution will be, but beware of promoting the mindset that obesity is ok and it’s a discrimination issue, because unfortunately that’s not the case.

  11. MNb says

    More active lives with regular exercise might be more attainable, but not enjoyable for me with my utter lack of discipline. Then again I don’t really mind my big belly.
    Many of those health measures seem to aim at increasing life expectancy. I am not so sure if I like that aim, given the fact that the higher the age the bigger the chance of health issues. That’s something not many people seem to think about – that the extra years very well might be years of agony.
    A somewhat unhealthy lifestyle might have the advantage of avoiding this:

  12. filethirteen says

    Avoid wishful thinking. It’s well known that obesity significantly reduces quality of life (HRQL).

    “Not only do obese individuals die earlier, but their quality of life is severely compromised; they are far more likely to suffer from diabetes and its complications — kidney failure, blindness, leg amputations — as well as stroke, breast and colorectal cancer, osteoarthritis and depression” (quote by Dr Susan Jebb, but I can’t find the original paper cited)

  13. smrnda says

    I recall a friend of mine who is very athletic being told he was ‘overweight’ by a doctor. He pulled up his shirt, pointed to his six pack abs and said “so, where am I supposed to lose this weight from?” the doctor them sheepisly said that the charts were just ‘guidelines’ for which there were exceptions. He wanted to know why the doctor didn’t ask him about thing like this *before* declaring him to be overweight , or whether the doctor just enjoyed telling people they were fat.

  14. says

    As a country England is definitely getting much fatter. During the 1960′s and seventies pupils that went to school during those decades in the UK will probably all remember the single large child in the class? In fact most will tell you there one often just one fat kid in the whole building. Today around twenty five percent of kids in every classroom are probably weighing too much than is considered as a healthy size.


  1. [...] Mano Singham directs us to a New England Journal of Medicine article that discusses some common misconceptions about obesity and some common ideas that are without foundation. If you are a faculty member at a university, you probably have access to the article itself, which [...]

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