This new commentary reviews common myths and presumptions about obesity and also provides some useful evidence-based concepts about overweight and obesity.
Many beliefs about obesity persist in the absence of supportingscientific evidence (presumptions); some persist despite contradicting evidence (myths). The promulgation of unsupported beliefs may yield poorly informed policy decisions, inaccurate clinical and public health recommendations, and an unproductive allocation of research resources and may divert attention away from useful, evidence-based facts.
• Do small sustained changes in energy intake or expenditure produce large, long-term weight changes?
According to the authors, predictions suggesting that large changes in weight will accumulate indefinitely in response to small sustained lifestyle modifications rely on the half-century-old 3500-kcal rule, which equates a weight alteration of 0.45 kg (1 lb) to a 3500-kcal cumulative deficit or increment. However, the original model was derived from short-term experiments predominantly performed in men on very-low-calorie diets. Recent studies have shown that individual variability affects changes in body composition in response to changes in energy intake and expenditure, with analyses predicting substantially smaller changes in weight (often by an order of magnitude across extended periods). For example, whereas the 3500-kcal rule predicts that a person who increases daily energy expenditure by 100 kcal by walking 1.6 km (1 mile) per day will lose 22.7 kg (>50 lb) over a period of 5 years, the true weight loss is only about 4.5 kg (10 lb), assuming no compensatory increase in caloric intake.
• How important is it to set realistic goals for weight loss?
Empirical data indicate no consistent negative association between ambitious goals and program completion or weight loss. Indeed, several studies have shown that more ambitious goals are 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.
Morning Report Questions
Q: What is the role of physical-education classes, in their current form, in reducing or preventing childhood obesity?
A: Physical education, as typically provided, has not been shown to reduce or prevent obesity. Findings in three studies that focused on expanded time in physical education indicated an increase in the number of days children attended physical-education classes, but the effects on body-mass index (BMI) were inconsistent across sexes and age groups. Two meta-analyses showed that even specialized school-based programs that promoted physical activity were ineffective in reducing BMI or the incidence of obesity. There is almost certainly a level of physical activity (a specific combination of frequency, intensity, and duration) that would be effective in reducing or preventing obesity. Whether that level is plausibly achievable in conventional school settings is unknown, although the dose-response relationship between physical activity and weight warrants investigation in clinical trials.
Q: Does breast-feeding have an effect on the development of obesity?
A: It has long been held that that persons who were breast-fed as infants are less likely to be obese later in life. Many studies with control for confounding (e.g., studies including within-family sibling analyses) as well as a randomized, controlled trial involving more than 13,000 children who were followed for more than 6 years provided no compelling evidence of an effect of breast-feeding on obesity. Although existing data indicate that breast-feeding does not have important antiobesity effects in children, it has other important potential benefits for the infant and mother and should therefore be encouraged.