Dietary intervention with vitamin D, calcium, and whey protein reduced fat mass and increased lean mass in rats

Abstract

The aim of the current study was to determine the effects and the mechanisms of inclusion of dietary whey protein, high calcium, and high vitamin D intake with either a high-sucrose or high-fat base diets on body composition of rodents. Male Wistar rats were assigned to either no whey protein, suboptimal calcium (0.25%), and vitamin D (400 IU/kg) diet (LD), or a diet containing whey protein, high calcium (1.5%), and vitamin D (10 000 IU/kg) diet (HD), and either high-fat (40% of energy) or high-sucrose (60%) base diets for 13 weeks. Liver tissue homogenates were used to determine [(14)C]glucose and [(14)C]palmitate oxidation. mRNA expression of enzymes related to energy metabolism in liver, adipose, and muscle, as well as regulators of muscle mass and insulin receptor was assessed. The results demonstrated that there was reduced accumulation of body fat mass (P = .01) and greater lean mass (P = .03) for the HD- compared to LD-fed group regardless of the background diet. There were no consistent differences between the LD and HD groups across background diets in substrate oxidation and mRNA expression for enzymes measured that regulate energy metabolism, myostatin, or muscle vascular endothelial growth factor. However, there was an increase in insulin receptor mRNA expression in muscle in the HD compared to the LD groups. In conclusion, elevated whey protein, calcium, and vitamin D intake resulted in reduced accumulation of body fat mass and increased lean mass, with a commensurate increase in insulin receptor expression, regardless of the level of calories from fat or sucrose.

Figure 1. Body weight and Calorie Intake

Body weights during dietary 13 week intervention with LD or HD diets with either a high fat or high sucrose base are expressed as mean±SE. There were no significant differences between the groups as evaluated by two-way analysis of variance. Calorie intake (B) values are expressed as means ± SE and the number of animals in each group is shown in the bar. Bars with different letters are significantly different as assessed by two-way analysis of variance.

Figure 2. Fat Mass and Lean Mass

Following 13 week dietary intervention with LD or HD diets with either a high fat or high sucrose base, fat mass (A) and lean mass (B) of animals was estimated by DXA. Values are expressed as mean ± SEM. Bars with different letters are significantly different as assessed by two-way analysis of variance (ANOVA).

Figure 3. Liver Substrate Oxidation

Following 13 week dietary intervention with LD or HD diets with either a high fat or high sucrose base, liver oxidation of glucose (A) and palmitate (B) was assessed. Values are expressed as mean ± SE (pmols CO₂/mg protein/hour). Bars with different letters are significantly different as assessed by two-way analysis of variance.

Figure 4. Liver ACC Activity

Following 13 week dietary intervention with LD or HD diets with either a high fat or high sucrose base animals were harvested. Western blot analyses was completed to assess hepatic activity of ACC employing total and phospho-specific antibodies and the quantification of the Western for phosphorylated/total ACC in the intervention groups are shown. Values are expressed as mean±SEM. There was no significant difference amongst the groups or between LD and HD groups when results were collapsed by main effect of base diet in GLM model.