Myths about obesity

Myths are defined as beliefs held to be true despite substantial refuting evidence; presumptions as beliefs held to be true for which convincing evidence does not yet confirm or disprove their truth; and facts as propositions backed by sufficient evidence to consider them empirically proven for practical purposes. What follow are examples of some common beliefs about obesity that are not supported by scientific evidence.

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

Predictions suggesting that large changes in weight will accumulate indefinitely in response to small sustained lifestyle modifications rely on the half-century-old 3,500kcal rule, which equates a weight alteration of 1lb (0.45kg) to a 3,500kcal cumulative deficit or increment. However, whereas the 3,500kcal rule predicts that a person who increases daily energy expenditure by 100kcal by walking one mile (1.6km) per day will lose more than 50lb (22.7kg) over a period of five years, the true weight loss is only about 10lb (4.5kg), assuming no compensatory increase in caloric intake, because changes in mass concomitantly alter the energy requirements of the body.

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

Indeed, several studies have shown that more ambitious goals are sometimes associated with better weight-loss outcomes. Furthermore, two studies showed that interventions designed to improve weight-loss outcomes by altering unrealistic goals resulted in more realistic weight-loss expectations but did not improve outcomes.

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

Within weight-loss trials, more rapid and greater initial weight loss has been associated with lower body weight at the end of long-term follow-up. Although it is not clear why some obese persons have a greater initial weight loss than others do, a recommendation to lose weight more slowly might interfere with the ultimate success of weight-loss efforts.

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.

Readiness does not predict the magnitude of weight loss or treatment adherence among persons who sign up for behavioural programmes or who undergo obesity surgery. The explanation may be simple – people voluntarily choosing to enter weight-loss programmes are, by definition, at least minimally ready to engage in the behaviours required to lose weight.

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

Physical education, as typically provided, has not been shown to reduce or prevent obesity. There is almost certainly a level of physical activity that would be effective in reducing or preventing obesity. Whether that level is plausibly achievable in conventional school settings is unknown.

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

A World Health Organization report states that persons who were breast-fed as infants are less likely to be obese later in life and that the association is “not likely to be due to publication bias or confounding”. However, a randomised, controlled trial provided no compelling evidence of an effect of breast-feeding on obesity.