Low intensity exercise and varying proportions of dietary glucose and fat modify milk and mammary gland compositions and pup growth

Exercise during pregnancy or lactation may create a competition for glucose between the exercising muscle and either the developing fetus or the lactating mammary gland. To test these two hypotheses, pregnant rats were randomly assigned to isoenergetic diets with varying levels of glucose (20, 40 or 60% by weight) and fat (30, 22 or 14%, respectively, by weight) and were rested (R) or exercised (E) on a motorized treadmill at 20 m/min, 60 min/d (low intensity), 7 d/wk throughout pregnancy and lactation. Main effects and selected interactions of diet and exercise during pregnancy and diet, exercise and litter size during lactation were tested using 3 x 2 and 3 x 2 x 2 factorial designs, respectively. Neither diet nor exercise affected pregnancy outcomes. In contrast, during lactation, milk and mammary gland compositions and pup growth were altered. Exercise produced higher milk protein concentrations (40% glucose diet) and lower milk lactose concentrations (20% glucose diet). Exercise also lowered mammary gland fat content and produced higher milk fat concentrations. The 60% glucose diet resulted in the highest milk fat concentrations, but pups of dams fed the 40% diet were heavier on lactation d 15 than pups of dams fed the 60% diet. Taken together, these results support the claim of decreased availability of glucose to the mammary gland for lactose synthesis during chronic low intensity exercise. Additionally, the best lactation performance was not supported by a high carbohydrate (60% glucose), lower fat (14%) intake. A more moderate carbohydrate (40% glucose), higher fat (22%) intake promoted greater pup weights at weaning, suggesting an overlooked role for macronutrient composition in optimizing lactation performance.

Effect of sucrose and fructose macronutrient diets on feeding behavior of rats

Different carbohydrate sources in animal diets can affect feeding behavior. The absence of a diet standard, thus, has the potential to introduce a confounding factor into experiments. The main objective of this study, therefore, was to determine if the choice of either sucrose or fructose as the pure carbohydrate in a carbohydrate diet ration would affect feeding behavior in rats. It was found that during the light and dark phases: 1) fructose-fed rats selected significantly less energy from carbohydrate than sucrose fed rats, 2) fructose-fed rats selected more protein and lipid energy than sucrose fed rats, and 3) the total caloric intakes of the two groups were not significantly different. Differing postingestive effects of sucrose and fructose with subsequent compensatory intake may explain these results. Two different carbohydrate sources resulted in different macronutrient selection patterns, thus demonstrating the importance of the nature of dietary carbohydrate in the regulation of feeding behavior in rats.