Rationale:

• Obesity results from an imbalance of energy expenditure and intake.

Evidence:

• Obesity is increasing in prevalence, particularly in persons with higher BMI levels (122).
• Obesity shortens life expectancy (123; 124; 125; 126). In older people (over age 75), WHR is a better predictor of risk than waist circumference or BMI.
• Prospective studies have shown that weight gain after ages 18 to 20 can predict future risk of heart disease and diabetes (127; 128).
• Obesity runs in families through genetic and environmental factors (129).
• Entry into a romantic partnership is associated with obesity (130), but sexual abuse is not (131).
• Prospective studies have shown that central obesity (132; 133) increases the risk of death from heart disease and cancer in women (134), as well as that of hypertension, stroke (135), dyslipidemia, and the metabolic syndrome (136), and that it can be assessed by the waist circumference (137; 138).
• In adults, 11 of 19 studies show a clear association between a short duration of sleep and increased weight (139); in older adults, short (5 hours or less) and long (8 or 9 hours) sleep durations are associated with obesity (140).
• Sedentary lifestyle is associated with obesity (141; 142; 143), enhanced risk of cardiovascular events (144; 145), and death (141).
• Additional epidemiologic and metabolic predictors for obesity have been identified, including cessation of smoking (146), familial factors (147), low metabolic rate (in some studies) (148), and genetic factors (129).
• Cessation of smoking increases body weight in men and women by up to 7 kg (149).
• Job stress and strain increased the risk of obesity and central adiposity (150).
• A BMI of <25 is normal for most people; overweight is BMI 25 to 29; and obesity is BMI 30 kg/m² (151; 152).
• Overeating produces obesity (101; 153).
• Regular weighing can reduce weight gain of female college freshmen (154).
• Population studies show that higher levels of dietary fat are associated with higher BMI (97; 98; 99).
• People who keep weight off tend to reduce fat intake (100).
• The risk of overweight is less in people who eat breakfast (105).
• Weight cycling among male athletes is associated with more weight gain than in nonathlete controls (155), but is not detrimental in women (156).

Comments:

• None.