Adaptation to overeating in lean and overweight men and women.

In groups of four, men and women in their 40s and 50s, some of them lean and some overweight, overate for 30 d by 1000 kcal/d (4186 kJ/d) more than they needed to maintain weight. On an average dietary mixture for Americans they gained a mean of 2.68 kg, and on a diet high in carbohydrate (60 per cent of energy) they gained 2.73 kg. However, on a diet high in protein and fat (70 per cent of energy), they gained significantly less, 1.75 kg. On all three diets the subjects should have gained 5 kg, if adipose tissue has an energy density of 6 kcal/g, and had there been no adaptation. There was adaptation, as evidenced by an average 7 per cent increase in thermogenesis, which was measured by 24-h direct and indirect calorimetry. Energy balances were calculated from: bomb calorimeter values for food and body waste; change in fuel stores from body composition measured by densitometry; and daily expenditure estimated from the net food intake needed to maintain body weight during a 30-d control period. During overeating, energy intake matched energy losses (including fuel storage) for the average diet and the high-carbohydrate diet, but on the diet high in protein and fat energy intake exceeded losses by more than 500 kcal/d (2093 kJ/d). Thus smaller than expected weight gains from overeating (luxuskonsumption) were largely explained by increased thermogenesis, except when the diet was high in protein and fat. Lean and overweight subjects did not differ in weight gain, loss of energy in urine and faeces, or thermogenesis from overeating.