Chapter overview Definition Aetiology Genetic influence Prevalence Health risks Physical inactivity and obesity Exercise as therapy Physical activity recommendations Summary
The questions... How is obesity defined and how does it arise? Is there an epidemic of obesity? If so, are there important risks to the health of the individual and the population? Does inactivity lead to obesity? Can physical activity help in the management of obesity?
Criteria for overweight and obesity and waist circumference cut-off points with associated disease risk Risk relative to normal weight and waist circumference BMI (kg m 2 ) Men < 102 cm, women < 88 cm Men ≥ 102 cm, women ≥ 88 cm Underweight Normal Overweight Obesity (class I) Obesity (class II) Extreme obesity (class III) < 18.5 18.5–24.9 25.0–29.9 30.0–34.9 35.0–39.9 ≥ 40.0 Not increased Increased High Very high Extremely high Not increased Increased High Very high Extremely Extremely high
Weight loss after prolonged fasting under medical supervision
Influence of weight loss and weight gain on 24-hour energy expenditure
Reduced energy intake and increased expenditure with injection of the satiety hormone oxyntomodulin
Genes are a strong determinant of body fatness – and particularly of visceral fat
BMI values of adopted children are associated with those of their biological parents
Gain in weight and visceral fat in monozygotic twins after overfeeding
Leptin replacement reduced body fatness in three leptin-deficient individuals
Walking or cycling to work is associated with lower risk for obesity
High levels of moderate activity are associated with lower weight gain after age 45 Note: Activity recorded as MET-h/week over the previous ten years; participants 15,000 US adults aged 53–57.
Low levels of physical activity predispose to weight gain
Physical characteristics, energy expenditure and physical activity levels in Mexican Pima Indians and US Pima Indians Mexican Pima Indians (17 female/23 male) US Pima Indians (17 female/23 male) Age (years) Height (cm) Weight (kg) Fat (%) Fat mass (kg) RMR (kcal/day) TEE (kcal/day) TEE (kcal/kgFFM/day) PAL 36.6 ± 11.4 163 ± 9 66.5 ± 12.6 29 ± 10 16.7 ± 6.7 1529 ± 223 3010 ± 722 3156 ± 415 1.97 ± 0.34 37.2 ± 12.4 166 ± 7 92.8 ± 22.4 41 ± 10 33.5 ± 14.1 1881 ± 327 2940 ± 514 2805 ± 415 1.57 ± 0.16
Obese individuals spend more time sitting, and less time standing and moving around Note: Data obtained using accelerometers and inclinometers.
Temporal changes in surrogate measures of physical activity track population changes in obesity prevalence
Can physical activity help in the management of obesity?
Duration of weekly exercise is related to weight loss in overweight and obese women Note: Intake of energy and fat restricted in addition to exercise.
Exercise-induced weight loss is influenced by genetic factors Note: Data from seven pairs of monozygotic twins.
Diet/exercise intervention is associated with loss of subcutaneous and visceral adipose tissue Note: Magnetic resonance images at level of lumbar spine for a man and a woman. Mean weight loss was 11 kg over a 16-week intervention.
Drugs licensed for obesity management Drug nameMechanismMean weight lossOther benefitsPossible adverse effects Orlistat Intestinal lipase inhibitor. Inhibits the breakdown of fat. 2.9 kg (2.5–3.2 kg). Average across 16 trials. Reduced risk of diabetes, improved TC and LDL-C concentrations. Improved BP and glycaemic control in patients with diabetes. Gastrointestinal side effects and slightly lowered HDL-C concentrations. Sibutramine Inhibits the reuptake of noradrenalin and serotonin at receptor sites that affect food intake. 4.2 kg (3.6–4.7 kg). Average across ten trials. Improved HDL-C and TG concentrations. Dry mouth, dizziness, nausea, constipation, headaches, depression and raised BP. Rimonabant Cannabinoid-1 receptor antagonist. (Stimulation of cannabinoid-1 receptors in the brain promotes eating). 4.7 kg (4.1–5.3 kg). Average across four trials. Improved HDL-C and TG concentrations. Improved BP and glycaemic control in patients with diabetes. Dizziness, nausea, diarrhoea, anxiety and depression.
Is weight loss in the obese hazardous to health?
Hazard ratios and 95% CIs of total mortality 1982–99 by intention to lose weight in 1975 and weight change 1975–81 Intention to lose weight (and weight change) Hazard ratioConfidence intervalP value Yes (loss) Yes (stable) Yes (gain) No (loss) No (stable) No (gain) 1.87 0.84 0.93 1.17 1.00 1.58 1.22–2.87 0.49–1.48 0.55–1.56 0.82–1.66 N/A 1.08–2.30 0.004 0.56 0.78 0.40 N/A 0.018
Summary I Obesity is an excess of body fat that endangers health. It is most commonly determined as BMI of 30 kg m 2 or over. Elevated waist circumference is another useful marker. Obesity develops due to an imbalance between energy intake and expenditure. Genes appear to play a major role in determining susceptibility to obesity. The prevalence of obesity has increased in many countries over the last few decades. Obesity, particularly severe obesity, increases the risk of premature mortality, type 2 diabetes, CVD, some cancers and osteoarthritis. The extent to which overweight increases these risks is less certain.
Summary II Observational evidence suggests that physical inactivity is associated with the development of obesity. Exercise can be effective in the management of obesity, particularly mild obesity. It is most effective when combined with diet. Weight regain after weight loss is common, but long-term maintenance of weight loss is possible in individuals who maintain healthy dietary and exercise habits. Recommendations suggest that 45–60 mins/day of exercise is needed to prevent obesity, but 60–90 mins/day to prevent weight regain in formerly obese individuals.