Obesity: A Global Public Health Challenge

The problem of excess weight gain and obesity is difficult for many scientists and doctors to understand because it seems a simple consequence of eating too much or doing too little. The remedy seems simple—to reduce intake or increase exercise. However, soon after I started running obesity clinics it became obvious that the obesity problem was more complex than that. A patient's failure to maintain any weight loss required an understanding of the patient's energy needs, and with more sophisticated analyses it soon became clear that different individuals have markedly different energy requirements. An individual's average needs, assessed over a month, may range from 1500 kcals/day to 3500 kcals/day or more. We then found, with whole body calorimetry, that individual energy expenditures at rest were astonishingly constant, with <1% differences over 24 h, unless we were considering young menstruating women who were shown to have a monthly cyclical resting metabolic rate. Interindividual differences depended on the patient's age, sex, size, and degree of physical activity. Given also that their mean weight gain was usually 0.5–1 kg/year, this merely amounted to a mean excess daily intake of 10–20 kcals/day over the year, a difference that could not be measured. But people, for social and other reasons, may vary their day's intake by perhaps 1000–1500 kcals during the week, implying there must be an extraordinary degree of medium and long-term appetite control. It then became clear that obese individuals adapted as they gain weight and changed what we crudely called their “energy set-point.” So on slimming, their behavioral, hormonal and autonomic nervous system responses resist weight loss, thereby helping to explain why most people, however intelligent and committed, after slimming find they have regained most if not all of their weight loss after 1–2 years. Many of these features were recognized in …