Body Composition And Hormonal Responses To A Carbohydrate-Restricted Diet Jeff S. Volek, Ph.D., R.D. (University of Connecticut, Storrs, CT) The finding in several studies that very low-carbohydrate diets (VLCKD) result in greater weight loss compared to low-fat diets is intriguing and important, but perhaps more clinically significant is the question: do VLCKD impact the composition or regional location of weight loss? The studies that have assessed body composition indicate that VLCKD diets may result in preferential loss of fat mass, especially if the caloric reduction is small. For example, we reported that a VLCKD with minimal energy restriction in normal-weight men resulted in significant decrease in body mass (-2.2 kg), entirely accounted for by a decrease in fat mass (-3.3 kg) and concomitant increases in lean body mass (+1.1 kg). Future well-controlled studies should be done to determine if VLCKD result in preferential loss of fat and/or spare protein losses. Another important question is related to the location of the weight loss. Upper body fat carries a greater health risk than fat stored in other regions of the body and thus an effective weight loss approach should consider the regional distribution of fat loss. Using dual-energy X-ray absorptiometry, we have observed that a VLCKD results in a preferential loss of fat in the trunk region, which was three-fold greater compared to that observed on a low-fat diet. The mechanisms regulating composition of weight loss and distribution of fat loss during VLCKD diets remain unclear. It is possible that VLCKD affect hormones that impact nutrient partitioning. Significant reductions in insulin are commonly observed on VLCKD and this could release the normal inhibition on lipolysis and allow for greater fat loss. Ketones could also act to spare catabolism of protein (muscle) on VLCKD. Other hormones that have anabolic (e.g., testosterone, growth hormone, IGF-I, etc.) and catabolic (e.g., cortisol, glucagons, etc.) actions have not been studied extensively on VLCKD, but might play a role in regulating the composition and site-specific location of weight loss. Body Composition And Hormonal Responses To A Carbohydrate-Restricted Diet Jeff S. Volek, Ph.D., R.D. (University of Connecticut, Storrs, CT) The finding in several studies that very low-carbohydrate diets (VLCKD) result in greater weight loss compared to low-fat diets is intriguing and important, but perhaps more clinically significant is the question: do VLCKD impact the composition or regional location of weight loss? The studies that have assessed body composition indicate that VLCKD diets may result in preferential loss of fat mass, especially if the caloric reduction is small. For example, we reported that a VLCKD with minimal energy restriction in normal-weight men resulted in significant decrease in body mass (-2.2 kg), entirely accounted for by a decrease in fat mass (-3.3 kg) and concomitant increases in lean body mass (+1.1 kg). Future well-controlled studies should be done to determine if VLCKD result in preferential loss of fat and/or spare protein losses. Another important question is related to the location of the weight loss. Upper body fat carries a greater health risk than fat stored in other regions of the body and thus an effective weight loss approach should consider the regional distribution of fat loss. Using dual-energy X-ray absorptiometry, we have observed that a VLCKD results in a preferential loss of fat in the trunk region, which was three-fold greater compared to that observed on a low-fat diet. The mechanisms regulating composition of weight loss and distribution of fat loss during VLCKD diets remain unclear. It is possible that VLCKD affect hormones that impact nutrient partitioning. Significant reductions in insulin are commonly observed on VLCKD and this could release the normal inhibition on lipolysis and allow for greater fat loss. Ketones could also act to spare catabolism of protein (muscle) on VLCKD. Other hormones that have anabolic (e.g., testosterone, growth hormone, IGF-I, etc.) and catabolic (e.g., cortisol, glucagons, etc.) actions have not been studied extensively on VLCKD, but might play a role in regulating the composition and site-specific location of weight loss.