We suggest that an exposure of mice to HP diets or a corresponding leucine supplementation has no significant effect on energy homeostasis and UCP expression compared with AP diets when feeding a low-fat diet. The use of high-quality whey protein might at least in part explain the results obtained.

Background: It has been hypothesized that the arginine:lysine ratio of dietary proteins influences cholesterol concentrations in plasma and liver of men and animals. This study was performed to test this hypothesis in rats by using diets with various concentrations of arginine and lysine, differing in their arginine:lysine ratios. Methods: Two experiments with growing rats were performed, some of which received diets containing 4.5, 9 or 18 g arginine/kg and 9 or 18 g lysine/kg, respectively, for a period of 21 days. In the first experiment, a cholesterol-free diet was used; in the second experiment, a diet supplemented with cholesterol and sodium cholate as hypercholesterolaemic compounds was used. Results: In experiment 1, increasing the arginine concentration lowered HDL and plasma cholesterol concentration; however, cholesterol concentrations in liver, LDL and VLDL remained unchanged. In experiment 2, increasing the arginine concentration lowered HDL cholesterol and increased liver cholesterol (p < 0.05); cholesterol concentrations in plasma, LDL and VLDL remained unchanged. The only effect of the dietary lysine concentration concerned the effect on VLDL and liver cholesterol concentration, which were both lower in rats fed the diets with 18 g lysine/kg than in those fed the diets with 9 g lysine/kg (p < 0.05). Varying the dietary arginine:lysine ratio between 0.25 and 2.0 had no influence on cholesterol concentration in LDL and VLDL in both experiments; HDL cholesterol concentration was lowered by increasing this ratio (p < 0.05). Conclusion: The present study does not support the hypothesis that an increase in the dietary arginine:lysine ratio causes hypocholesterolaemic effects in rats.

High dietary protein (P) intake can improve glucose homeostasis, decrease body weight gain, and increase energy expenditure (EE). Leucine (Leu) was suggested to be involved in the regulation of genes stimulating energy metabolism. Therefore, we aimed to study the effects of high P and a high Leu containing adipogenic diets in mice. Male C57BL/6 mice were fed for 20 wks high fat diets (20%) containing either 10% (AP, control) or 50% whey P (HP). A third group was exposed to AP supplemented with L‐Leu (AP+L) as contained in HP. HP feeding and Leu supplementation resulted in significantly (P<0.05) lower food intake, reduced body weight gain (20.7±0.8, 14.8±1.4 and 9.7±0.8 g for AP, AP+L and HP, respectively), lower food energy efficiency (2.14±0.08, 1.57±0.11 and 1.11±0.08 g/MJ for AP, AP+L and HP, respectively), lower body fat mass (quantitative nuclear resonance), lower liver triacylglycerol concentrations, and higher lean body mass as well as higher weights of m. quadriceps and higher postabsorptive 15N‐lysine incorporation into skeletal muscle. EE (indirect calorimetry) was not different between groups. Parameters of glucose homeostasis were significantly (P<0.05) improved in HP and AP+L fed mice. Effects of Leu supplementation are generally intermediate to those of the HP as compared to AP. We suggest a role of Leu at the increase of EE; however, an expected higher uncoupling protein gene expression was not detected.