Thinking Critically about Obesity

Philosophers looking for excellent examples to use in critical thinking classes might be well served by our thinking about overweight, obesity, and weight loss. “Myths, Presumptions, and Facts about Obesity,” published in the New England Journal of Medicine today reviews shoddy reasoning abut obesity and asks why it is we continue to believe things to be true on the basis of little or no evidence in their favour or even with substantial evidence against.

Here’s Gina Kolata writing about the article in the New York Times,

“Myths and unproven assumptions about obesity and weight loss that have been repeated so often and with such conviction that even scientists like David B. Allison, who directs the Nutrition Obesity Research Center at the University of Alabama at Birmingham, have fallen for some of them.Now, he is trying to set the record straight. In an article published online today in The New England Journal of Medicine, he and his colleagues lay out seven myths and six unsubstantiated presumptions about obesity. They also list nine facts that, unfortunately, promise little in the way of quick fixes for the weight-obsessed.” Myths of Weight Loss Are Plentiful, Researcher Says

The myths, “beliefs held true despite substantial evidence refuting them,” are:

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

2. Setting realistic goals in obesity treatment is important because otherwise patients will become frustrated and lose less weight

3. Large, rapid weight loss is associated with poorer long-term weight outcomes than is slow, gradual weight loss

4. Assessing the stage of change or diet readiness is important in helping patients who seek weight-loss treatment

5. Physical-education classes in their current format play an important role in preventing or reducing childhood obesity

6. Breast-feeding is protective against obesity

7. A bout of sexual activity burns 100 to 300 kcal for each person involved”

The six presumptions, believed to be true but without evidence in their favour, are:

“1. Regularly eating (vs. skipping) breakfast is protective against obesity
2. Early childhood is the period during which we learn exercise and eating habits that influence our weight throughout life
3. Eating more fruits and vegetables will result in weight loss or less weight gain, regardless of whether one intentionally makes any other behavioral or environmental changes
4. Weight cycling (i.e., yo-yo dieting) is associated with increased mortality
5. Snacking contributes to weight gain and obesity
6. The built environment, in terms of sidewalk and park availability, influences obesity”

Why do we, where that includes many health care professionals, believe things to be true when there is no evidence in their favour (the presumptions) or worse when there is evidence against them (the myths)?

In the section of the article called “Knowing and Not Knowing” Allison discusses various sorts of biases that influence our thinking about health and weight. Writes Allison:

“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).”

The 9 facts are less interesting, as facts tend to be! Diets don’t work in the long term. Exercise does help keep weight off. Heredity is important but is not destiny. Weight loss is greater with programs that provide meals. Some prescription drugs help with weight loss and maintenance. Weight-loss surgery is a good solution for some people. For overweight children programs that involve the whole family work best. Exercise is good for your health regardless of its effect on your weight. And in order to maintain a new lower weight you need to continue the conditions that led to weight loss.


“Myths, Presumptions, and Facts about Obesity”

Krista Casazza, Ph.D., R.D., Kevin R. Fontaine, Ph.D., Arne Astrup, M.D., Ph.D., Leann L. Birch, Ph.D., Andrew W. Brown, Ph.D., Michelle M. Bohan Brown, Ph.D., Nefertiti Durant, M.D., M.P.H., Gareth Dutton, Ph.D., E. Michael Foster, Ph.D., Steven B. Heymsfield, M.D., Kerry McIver, M.S., Tapan Mehta, M.S., Nir Menachemi, Ph.D., P.K. Newby, Sc.D., M.P.H., Russell Pate, Ph.D., Barbara J. Rolls, Ph.D., Bisakha Sen, Ph.D., Daniel L. Smith, Jr., Ph.D., Diana M. Thomas, Ph.D., and David B. Allison, Ph.D.

N Engl J Med 2013; 368:446-454 January 31, 2013 DOI: 10.1056/NEJMsa120805

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