Physiologic studies reported here show that obese persons use carbohydrate, fat, and protein normally during rest and exercise and are not unusually efficient in the use of these energy substrates. Obese subjects mobilize fat stores for energy as readily as normals. It is not necessary to overeat to become obese; the decrease of basal calorie requirements with age is such that obesity can develop with advancing age while exercise remains constant, even if food intake is reduced to some extent. Subjects tested were persons of various ages whose intake of food ranged from that of hypophagia to that of hyperphagia and whose body weights varied similarly.
Nelson RA, Anderson LF, Gastineau CF, Hayles AB, Stamnes CL. Physiology and Natural History of Obesity. JAMA. 1973;223(6):627–630. doi:10.1001/jama.1973.03220060013004