title: A low-glycemic diet lifestyle intervention improves fat utilization during exercise in older obese humans.
abstract: OBJECTIVE
  To determine the influence of dietary glycemic index on exercise training-induced adaptations in substrate oxidation in obesity.
  
  
  METHODS
  Twenty older, obese individuals undertook 3 months of fully supervised aerobic exercise and were randomized to low- (LoGIX) or high-glycemic (HiGIX) diets. Changes in indirect calorimetry (VO2 ; VCO2 ) were assessed at rest, during a hyperinsulinemic-euglycemic clamp, and during submaximal exercise (walking: 65% VO2 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 VO2 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 during exercise was unchanged in the LoGIX group but increased in the HiGIX group (P < 0.05). However, fat oxidation during exercise expressed in relation to changes in body weight was increased in the LoGIX group (+10.6 ± 3.6%; P < 0.05). Fasting IMCL was unchanged, however, extramyocellular lipid was reduced (P < 0.05) after LoGIX.
  
  
  CONCLUSIONS
  A LoGIX/exercise weight-loss intervention increased 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.
authors.affiliation: Department of Pathobiology, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Thomas P J
authors.initials: TP
authors.lastname: Solomon
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Haus
authors.forename: Marc A
authors.initials: MA
authors.lastname: Cook
authors.forename: Chris A
authors.initials: CA
authors.lastname: Flask
authors.forename: John P
authors.initials: JP
authors.lastname: Kirwan
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D000368:Aged; D000375:Aging / Q000378:metabolism; D050528:Diet, Carbohydrate-Restricted; D015444:Exercise / Q000502:physiology*; D005081:Exercise Therapy; D005260:Female; D038321:Glycemic Index; D006801:Humans; D008019:Life Style; D050356:Lipid Metabolism; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism / Q000628:therapy*; D061217:Weight Reduction Programs