Food Intake, Energy Balance and Serum Leptin Concentrations in Rats Fed Low-Protein Diets

Abstract

Studies examining the effects of low-protein diets on food intake and body weight have shown varied results. Many researchers have found low dietary protein 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 of dietary protein (2%, 5%, 8%, 10%, 15% vs. 20% casein) to determine the dose-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 occurred 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-protein 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 group 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 fed 20% casein. Serum leptin concentrations were positively associated with body fat content (r(2) = 0.763, P < 0.001). Increased serum leptin concentrations in the presence of increased food intake is suggestive of a state of leptin resistance. This animal model may provide important insights into diet-induced obesity.

A free-choice high-fat high-sugar diet induces glucose intolerance and insulin unresponsiveness to a glucose load not explained by obesity

“…Furthermore, as the chow diet contains 22% protein, a reduction of B30% of this diet will still result in a sufficient amount of protein for healthy growth (that is, comparable to a 15% protein diet). 40,41 In summary, the specific combination of a diet of saturated fat and a sugar solution, but not fat or sugar alone, results in rapid glucose intolerance and insulin unresponsiveness to a glucose load, which is not explained by levels of circulating lipids or fat mass accumulation. These data, together with previous data showing effects of a HFHS-choice diet on hypothalamic neuropeptide expression, 15 imply a role for the central nervous system in these diet-induced alterations in glucose metabolism, and in the early transition from glucose intolerance to type 2 diabetes mellitus.…”

Administration of bovine anti-IGF-1 immunoglobulin to dietary protein deficient rats alters dietary intake and plasma IGF-1 binding profiles, but does not affect change in body mass

“…Severe nutrient deficiencies suppress dietary intake while marginal deficiencies are stimulatory. Accordingly, in rats, Du et al (2000) demonstrated increased dietary intake with moderate protein restriction (at or just below growth requirements), but decreased intake and BW in response to more severe protein restriction. This pattern of response, in addition to other factors that affect protein requirements and therefore intake (e.g.…”

“…The most outstanding effect observed was the severe reduction in growth rate and dietary intake and as a result of protein deprivation. Previous studies have also reported inhibitory effects of low-protein diets on food intake and BW (Miura et al, 1992;Du et al, 2000;Katsumata et al, 2002), while others have reported no effect, or an increase in these parameters (VandeHaar et al, 1991;Du et al, 2000;Katsumata et al, 2002). In this connection, Forbes (2000) outlined the general relationship between the concentration of an essential nutrient in food and the rate of voluntary food intake, which is associated with concomitant changes in growth rate and other production parameters (e.g.…”

“…This pattern of response, in addition to other factors that affect protein requirements and therefore intake (e.g. age, gender, psychological stress), may explain the varied reported dietary intake and growth responses to dietary protein content (Du et al, 2000).…”

Influência da desnutrição proteica sobre a expressão de fatores de transcrição envolvidos no processo de diferenciação da célula tronco mesenquimal medular

“…Os animais dos grupos controles receberam a ração normoprotéica; e os animais pertencentes aos grupos desnutridos, a ração hipoprotéica (DU; HIGGINBOTHAN;WHITE, 2000;BORELLI et al, 2007). Os animais foram submetidos aos ensaios experimentais quando o grupo desnutrido perdeu cerca de 20 % do peso inicial sendo que o peso e o consumo de ração foram avaliados a cada 48 horas .…”