ENHANCED FATTY ACID OXIDATION IS ASSOCIATED WITH IMPROVEMENTS IN INSULIN SENSITIVITY IN OBESE SUBJECTS

Abstract

Insulin resistance is associated with obesity and physical inactivity, both of which are further characterized by an impaired capacity for fatty acid oxidation. However, it is unknown what role an improved capacity for fatty acid oxidation may have in the improvement in insulin sensitivity following weight loss and exercise. PURPOSE To determine whether a program combining exercise with diet induced weight loss improves systemic fatty acid oxidation and also whether these alterations in fatty acid metabolism are directly associated with improvments in insulin resistance. METHODS 25 obese (BMI > 30 kg•m−2) volunteers (9 men and 16 women) without diabetes, aged 39 ± years completed a 16-week intervention of moderate exercise and caloric restriction. The exercise component consisted of 4–5 sessions/wk, 30–50 min/session of walking or stationary cycling. A reduction of 500–1000 kcal/day based on recent food records/history and a low fat (< 30% of calories from fat) diet was used to achieve a 10% weight loss. Changes in glucose disposal rates (Rd) during hyperinsulinemia (40 mU•m−2•min−1 euglycemia), total body fat and fat free mass (FFM) by DXA, abdominal fat and skeletal muscle fat distribution by computed tomography, physical fitness (VO2peak), and systemic post-absorptive fatty acid oxidation were determined. RESULTS Total body fat and regional fat depots were significantly reduced. VO2peak improved on average by 19% from 38.8 ± 1.2 to 46.0 ± 1.0 ml•kgFFM−1min−1 (p < 0.05). Insulin sensitivity improved 49 ± % from 6.7 ± 0.4 to 9.5 ± 0.5 mg•kgFFM−1•min−1 (p < 0.05). Rates of systemic fatty acid oxidation following an overnight fast increased from 1.16 ± 0.06 to 1.35 ± 0.05 mg•kgFFM−1•min−1 (p < 0.05), with the proportion of energy from fat increasing on average from 38% to 52%. The strongest predictor of the improvement in insulin sensitivity was the enhanced post absorptive fatty acid oxidation which accounted for 52% of the variance. CONCLUSION Exercise combined with weight loss enhances post-absorptive fatty acid oxidation, which is associated with improvements in insulin sensitivity in obesity.