Low‐ and High‐Carbohydrate Diets: Body Composition Differences in Rats

Objective : To determine differences in adipose tissue mass, cell size, and lipid metabolism transcripts and differences in composition of body weight loss and energy expenditure (EE) after isoenergetic, energy‐restricted intake of low‐carbohydrate/high‐fat/high‐protein (LC) and high‐carbohydrate/low‐fat/moderate‐protein (HC) diets. Research Methods and Procedures : Ten‐week old female Sprague‐Dawley rats were fed a high‐fat diet ad libitum for 8 weeks to induce weight gain and fat deposition. Weight‐matched rats were then assigned to isoenergetic LC (Atkins) and HC (American Dietary Association Exchange) diets for 10 weeks at 65% of ad libitum energy intake. Results : There was no significant difference in the serum lipid profiles or amount of body weight lost between the HC and LC groups, whereas a higher insulin sensitivity index ( p < 0.01) resulted from the HC compared with the LC diet. Compared with the post‐restriction LC group, the HC group demonstrated ( p < 0.05) higher EE during active hours, lower mRNA levels for the lipogenic genes peroxisome proliferator‐activated receptor γ2, lipoprotein lipase, and, adipocyte fatty acid binding protein, decreased adipocyte cell volume, and decreased fat mass. Discussion : Results indicated down‐regulation of lipogenic genes, decreased fat mass, and, therefore, improved body composition in the post‐restriction HC compared with the LC group. The small mean differences between the two diet groups ( p = 0.11) in 24‐hour EE over the 10 weeks of diet intervention would account for the majority of the lower mean body weights in the post‐restriction HC group. These data suggest that macronutrient composition of the diet influences body composition and indicate a distinction between HC and LC diets.