Food intake, energy balance and serum leptin concentrations in rats fed low-protein diets

Studies examining the effects of low-protein diets on food intake and body weight have shown varied results. Many researchers have found low dietary p rotein to increase food intake, while others have found no effect or even a decrease. In 63 male Sprague-Dawley rats, we examined several low levels o f dietary protein (2%, 5%, 8%, 10%, 15% vs. 20% casein) to determine the do se-response relationships between low dietary protein and food intake, body composition, energy balance and serum leptin concentrations. Food intake, over the range of low dietary protein, showed a quasi bell-shaped response curve with peak intake occurring in rats fed 8-10% casein. Peak feeding occ urred at or just below the estimated protein requirement of the rats (10-12 .5% casein). Compared to the 20% casein controls, food intake was severely reduced in rats fed 2% casein, while it was greater in the other low-protei n groups. The amount of body fat steadily increased between the 15% casein group and the 8% casein group, and sharply declined between the 5% casein g roup and 2% casein group. The change in body fat reflected both the change in food intake and altered energy partitioning. Serum leptin concentrations were greater in rats fed the 5 and 8% casein diets than in control rats fe d 20% casein, Serum leptin concentrations were positively associated with b ody fat content (r(2) = 0.763, P < 0.001). Increased serum leptin concentra tions in the presence of increased food intake is suggestive of a state of leptin resistance. This animal model may provide important insights into di et-induced obesity.