A low glycemic diet lifestyle intervention improves fat utilization during exercise in older obese humans

OBJECTIVE: To determine the influence of dietary glycemic index on exercise training-induced adaptations in substrate oxidation in obesity. DESIGN AND METHODS: Twenty older, obese individuals undertook 3-months of fully-supervised aerobic exercise and were randomised to low (LoGIX) or high glycemic (HiGIX) diets. Changes in indirect calorimetry (VO(2); VCO(2)) were assessed at rest, during a hyperinsulinemic-euglycemic clamp, and during submaximal exercise (walking: 65% VO(2)max, 200 kcal energy expenditure). Intramyocellular lipid (IMCL) was measured by (1)H-magnetic resonance spectroscopy. RESULTS: Weight loss (−8.6±1.1%) and improvements (P<0.05) in VO(2)max, glycemic control, fasting lipemia, and metabolic flexibility were similar for both LoGIX and HiGIX groups. During submaximal exercise, energy expenditure was higher following the intervention (P<0.01) in both groups. Respiratory exchange ratio (RER) during exercise was unchanged in the LoGIX group but increased in the HiGIX group (P<0.05). However, fat oxidation during exercise expressed relative to changes in body weight was increased in the LoGIX group (+10.6±3.6%; P<0.05). Fasting IMLC was unchanged, however extramyocellular lipid was reduced (P<0.05) after LoGIX. CONCLUSIONS: A low glycemic diet/exercise weight-loss intervention increases fat utilization during exercise independent of changes in energy expenditure. This highlights the potential therapeutic value of low glycemic foods for reversing metabolic defects in obesity.