Obesity Myths, Presumptions, and Facts

A study published today in the New England Journal of Medicine takes aim at the ever complex issue of obesity.  There are many beliefs about obesity in our society, yet most of them lack evidence.   A lot of them are flat-out made-up or the result of our own individual biases.  This lack of understanding only leads to more problems, especially when it comes to actually addressing the real problem.   (I discuss this in my pieces The Weight of the Nation and Unnatural Causes.)

The study was led by Dr. David Allison at the University of Alabama at Birmingham, and it used Internet searches of both popular media and scientific literature to classify myths and presumptions related to obesity.  The researchers identified seven obesity related myths, six presumptions, and nine facts that are relevant to forming public health policy and addressing the issue.


  • Small sustained changes in energy intake or expenditure will produce large, long-term weight changes.
  • Setting realistic goals for weight loss is important, because otherwise patients will become frustrated and lose less weight.
  • Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss.
  • It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment.
  • Physical-education classes, in their current form, play an important role in reducing or preventing childhood obesity.
  • Breast-feeding is protective against obesity.
  • A bout of sexual activity burns 100 to 300 kcal for each participant.


  • Regularly eating (versus skipping) breakfast is protective against obesity.
  • Early childhood is the period in which we learn exercise and eating habits that influence our weight throughout life.
  • 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.
  • Weight cycling (i.e., yo-yo dieting) is associated with increased mortality.
  • Snacking contributes to weight gain and obesity.
  • The built environment, in terms of sidewalk and park availability, influences the incidence or prevalence of obesity.


The article classifies the listed propositions as facts because there is sufficient evidence to consider them empirically proved.

  • Although genetic factors play a large role, heritability is not destiny; calculations show that moderate environmental changes can promote as much weight loss as the most efficacious pharmaceutical agents available.
  • Diets (i.e., reduced energy intake) very effectively reduce weight, but trying to go on a diet or recommending that someone go on a diet generally does not work well in the long-term.
  • Regardless of body weight or weight loss, an increased level of exercise increases health.
  • Physical activity or exercise in a sufficient dose aids in long-term weight maintenance.
  • Continuation of conditions that promote weight loss promotes maintenance of lower weight.
  • For overweight children, programs that involve the parents and the home setting promote greater weight loss or maintenance.
  • Provision of meals and use of meal-replacement products promote greater weight loss.
  • Some pharmaceutical agents can help patients achieve clinically meaningful weight loss and maintain the reduction as long as the agents continue to be used.
  • In appropriate patients, bariatric surgery results in long-term weight loss and reductions in the rate of incident diabetes and mortality.

Casazza et al. (2013) Myths, Presumptions, and Facts About Obesity. New England Journal of  Medicine, 368, 446-454.

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