Submitted on June 3, 2008
Revised on August 13, 2008
Accepted on August 28, 2008
Long-term effects of dietary glycemic index on adiposity, energy metabolism and physical activity in mice
Kelly B Scribner1, Dorota Pawlak2, Cristin M Aubin, Joseph Majzoub3, and David Ludwig4*
1 ALPCO Diagnostics
2 Children's Hopsital
3 Division of Endocrinology, Children's Hospital, Harvard Medical School
4 Harvard Medical School Boston
* To whom correspondence should be addressed. E-mail: david.ludwig{at}childrens.harvard.edu.
ABSTRACT Objective: A high glycemic index (GI) diet has been shown to increase adiposity in rodents; however, the long-term metabolic effects of GI diet have not been examined. Research Methods and Procedures: In this study, a total of 48 male 129SvPas mice were fed diets high in either rapidly absorbed carbohydrate (RAC, high GI) or slowly absorbed carbohydrate (SAC, low GI) for up to 40 weeks. Diets were controlled for macronutrient and micronutrient content, differing only in starch type. Body composition and insulin sensitivity were measured longitudinally by DEXA scan and oral glucose tolerance test, respectively. Food intake, respiratory quotient, physical activity and energy expenditure were assessed using metabolic cages. Results: Despite having similar mean body weights, mice fed the RAC diet had 40% greater body fat by the end of the study and a mean 2.2-fold greater insulin resistance compared with mice fed the SAC diet. Respiratory quotient was higher in the RAC group, indicating comparatively less fat oxidation. Although no differences in energy expenditure were observed throughout the study, total physical activity was 45% higher for the SAC-fed mice after 38 weeks of feeding. Discussion: We conclude that, in this animal model 1) the effect of GI on body composition is mediated by changes in substrate oxidation, not energy intake; 2) a high GI diet causes insulin resistance; 3) dietary composition can affect physical activity level.
