Glucose-restricted diets alter milk composition and mammary gland development in lactating rat dams

To examine the effects of chronic restriction of maternal dietary glucose on lactational performance, pregnant dams were fed one of four isoenergetic diets containing graded levels of glucose (0, 12, 24 and 60%) from d 2 of pregnancy to d 15 of lactation. Dams fed the 0% glucose diet produced colostrum with higher protein and lower lactose and fat concentrations than normal, but all pups born to these dams failed to survive more than 24 h postpartum. Dams fed glucose-restricted diets (12 and 24%) had significantly lower d 15 milk fat concentration than dams fed the control diet, but there were no differences in milk protein, lactose and glucose concentrations. On d 15, pups suckling dams fed the 12% glucose diet had significantly lower body weights than pups of dams fed 24 and 60% glucose diets. Restriction of dietary glucose to 12% resulted in significantly smaller mammary gland cell size but failed to produce any significant differences in mammary gland composition (protein, fat and glycogen). The results indicate that the level of glucose in the maternal diet is an important determinant of milk composition and that > 24% glucose is needed for optimal milk fat concentration, whereas 12% dietary glucose is sufficient to sustain normal milk lactose concentration. The altered lactational performance in response to dietary glucose restriction was not mediated through changes in mammary gland composition, but in part by the reduced mammary gland size.