Increased adiposity by a low fat diet with marginal protein deficiency

Abstract

Diet could play a key role in intervention of the obesity epidemic. However, it is unclear to what extent macronutrient composition can contribute to prevention and development of obesity. Previously, diet-induced obesity in animals has been accomplished by two separate methods: high fat or marginally protein deficient diets. This study investigated the interactive effects of these two dietary treatments on obesity development. Twenty-four male weanling Sprague-Dawley rats were fed one of 4 diets varying in macronutrients for 8 weeks. Diets were based on a 2x2 factorial with 2 levels of protein (10% and 25%) and 2 levels of fat (10% and 70%). Body composition was measured biweekly with dual energy X-ray absorptiometry. Initially, both 10%-protein groups consumed 36% more energy per body weight in an attempt to meet protein requirements. However, over 8 weeks, this compensation declined, and energy intake among all groups became nearly equal. As expected, between both 25%-protein groups, P25-F70-C5 (protein-fat-carbohydrate) developed more body fat (8.6%) after 2 weeks than P25-F10-C65 (7.1%, the lowest of all groups). Surprisingly, between both 10%-protein groups, it was P10-F10-C80 that had higher body fat (13.4%, the highest of all groups) than P10-F70-C20 (11.6%). The P10-F70-C20 group consumed less protein per lean body mass than P10-F10-C80, while attaining the same lean body growth, indicating higher protein utilization. These results suggest that under conditions of marginal protein deficiency, high dietary fat may have decreased degradation of essential ketogenic amino acids, such as leucine. There was no difference in expression of fatty acid synthase mRNA in liver between P10-F10-C80 (highest adiposity) and P25-F10-C65 (lowest adiposity). This indicates that adipose tissue may be responsible for increased lipogenesis in P10-F10-C80.