Dietary-induced severe obesity: exercise implications.

A rat model for severe obesity has been developed by feeding the animals a fat-rich, sugar-rich diet. The concentration of fat in the diet was similar to what most Americans consume (about 40% kcal from fat). Calories from sugar was calculated to be 40.6%. As adults, body fat content in these animals averaged 61 or 51%, depending on whether the fat-rich, sugar-rich diet caused hyperphagia. The rate of body fat accretion in these severely obese rats raised in litters of four was estimated to be 1.78 +/- 0.12 (SE) g X d-1 (61% body fat) or 0.9 +/- 0.03 g X d-1 (51% body fat). In contrast, lean rats eating a diet of Purina chow deposited fat at a rate of 0.20 +/- 0.02 g X d-1, resulting in a carcass fat content of 18%. Preliminary evidence based on adult body weights of sugar-fed rats suggests that sucrose alone can cause severe obesity similar to that seen with dietary fat alone. Currently, an attempt is being made to determine how dietary fat and/or dietary sugar work to produce severe obesity. One possibility is that dietary fat in the form of a chylomicron and dietary sugar in the form of a very low density lipoprotein may modify adipose tissue lipoprotein lipase activity. This enzyme acts as a gatekeeper for circulating triglycerides entering the adipocyte. It is our belief that the results obtained will help to lay the groundwork for determination of the role of exercise in weight control.