Nutritional Restriction and Activity Thermogenesis

Ninety sedentary subjects, aged 25-55, who live \<10 miles from Rochester will be recruited. This age range has been selected to enable us to study individuals at the peak age-range of obesity and over-weight prevalence and to avoid issues of menopause. Subjects will not be eligible for consideration if they take two or more bouts of exercise/week or participate in sports for more than 2 hours/week. Subjects with predicted weight maintenance energy requirements of \<2000 kcal/day will have been excluded at screening. This is because when we come to underfeeding by 1000 kcal/day, we want to avoid feeding any volunteer \<1000 kcal/day, for safety \& compliance reasons. (A) LEAN: 30 (15F,15M) lean subjects; BMI \<25 kg/m2. Each lean subject will be individually matched for height (+3cm) and age (+3 years) to an obese subject so as to establish comparable groupings for body size. Subjects will have been weight-stable for six months (B) OBESE: 30 (15F,15M) obese subjects; BMI 30-35 kg/m2. Subjects will have been weight-stable for six months (C) POST-OBESE: 30 (15F,15M) patients will have had a previous BMI \>30 kg/m2 and a weight loss sufficient to achieve a BMI of \<26 kg/m2 maintained for at least 2 months (with weight fluctuation during this period of \<1 kg) (94). We will attempt to match these subjects to the obese subjects as described above.