title: Metabolic responses to high glycemic index and low glycemic index meals: a controlled crossover clinical trial.
abstract: BACKGROUND
  The consumption of low glycemic index (LGI) foods before exercise results in slower and more stable glycemic increases. Besides maintaining an adequate supply of energy during exercise, this response may favor an increase in fat oxidation in the postprandial period before the exercise compared to high glycemic index (HGI) foods. The majority of the studies that evaluated the effect of foods differing in glycemic index on substrate oxidation during the postprandial period before the exercise are acute studies in which a single meal is consumed right before the exercise. The purpose of this study was to investigate the effect of consuming two daily HGI or LGI meals for five consecutive days on substrate oxidation before the exercise and in the concentrations of glucose, insulin and free fatty acids before and during a high intensity exercise.
  
  
  METHODS
  Fifteen male cyclists, aged 24.4 ± 3.8 years, with body mass index of 21.9 ± 1.4 kg.m⁻² and a V(O2 max) of 70.0 ± 5.3 mL.kg⁻¹.min⁻¹, participated in this crossover study. All test meals were consumed in the laboratory. On days 1 and 5, substrate oxidation (30 minutes before and 90 minutes after breakfast (HGI or LGI)) and diet-induced thermogenesis (90 minutes postprandial) were assessed before the exercise. The levels of glucose, insulin, and free fatty acids were determined during 2 h after breakfast on these same days. Ninety minutes after breakfast, subjects completed a 30 min cycloergometric exercise at 85 to 95% of their maximum heart rate, during which lactate concentrations were assessed.
  
  
  RESULTS
  The consumption of HGI meals resulted in higher areas under the glycemic and insulinemic curves in the postprandial period. However, glycemia did not differ by study treatment during exercise. There were no differences in free fatty acids in the postprandial period or in lactate levels during exercise. LGI meals resulted in lower fat oxidation and higher carbohydrate oxidation than the HGI meal in the postprandial period.
  
  
  CONCLUSIONS
  The results do not support a differential glycemia according to glycemic index during exercise. The ingestion of LGI foods did not lead to higher fat oxidation relative to the ingestion of HGI foods.
authors.affiliation: Departament of Nutrition and Health, Federal University of Viçosa, Avenida PH Rolfs, s/n, Viçosa, Minas Gerais, 36570-000, Brazil.
authors.forename: Paula G
authors.initials: PG
authors.lastname: Cocate
authors.forename: Letícia G
authors.initials: LG
authors.lastname: Pereira
authors.forename: João C B
authors.initials: JC
authors.lastname: Marins
authors.forename: Paulo R
authors.initials: PR
authors.lastname: Cecon
authors.forename: Josefina
authors.initials: J
authors.lastname: Bressan
authors.forename: Rita C G
authors.initials: RC
authors.lastname: Alfenas
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001786:Blood Glucose / Q000032:analysis; D018592:Cross-Over Studies; D004032:Diet; D004040:Dietary Carbohydrates / Q000008:administration & dosage* / Q000378:metabolism; D002149:Energy Intake; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D038321:Glycemic Index; D006801:Humans; D007328:Insulin / Q000097:blood*; D008297:Male; D019518:Postprandial Period; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin