Effect of diet on insulin sensitivity and energy balance

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DESCRIPTION (provided by applicant): The broad, long-term objective of this research proposal is to improve the health and well being of the elderly via decreased risk for type 2 diabetes. The specific aim of the project is to examine the influence of an ad libitum 12- week low-fat/simple-carbohydrate diet, with and without aerobic exercise training, on body mass, energy balance, and insulin sensitivity in older subjects with impaired glucose tolerance. Preliminary data indicate that consumption of a low-fat/complex-carbohydrate diet, with no attempt at energy restriction, results in loss of body weight and improvement in insulin sensitivity. We hypothesize that replacement of dietary fat with simple rather than complex-carbohydrates will result in similar improvements in health. Thirty-six overweight men and women aged 55-80 years with impaired glucose tolerance will be randomized into one of three groups. Group 1 will receive a control diet (similar to baseline intake), group 2 will receive a low-fat/simple-carbohydrate diet (17% fat, 16% protein, 67% carbohydrate, 9g fiber/1000kcal), and group 3 will receive an identical low-fat diet and be placed in an aerobic exercise training program (4d/week, 80% VO2ma,). Body composition will be measured using air displacement plethysmography, energy and macronutrient metabolism will be measured using whole room calorimetry and de novo lipogenesis, and insulin sensitivity will be measured using a euglycemic-hyperinsulinemic clamp. Given the increasing prevalence of type 2 diabetes in the elderly U.S. population, completion of this project will more clearly define the specific dietary and exercise interventions that have the greatest potential positive impact on health in older individuals.