EFFECT OF TRAINING ON RESPONSE TO A GLUCOSE-LOAD ADJUSTED FOR DAILY CARBOHYDRATE INTAKE

From responses to identical absolute glucose loads in trained (T) and untrained (UT) subjects, it has been inferred that training promotes health by reducing glucose levels and insulin secretion. To mimic daily living conditions, we studied responses to oral glucose loads making up identical fractions of daily carbohydrate intake (i.e., same relative glucose load) in seven T and eight UT males [maximal O2 uptake (VO2 max) 76 +/- 2 vs. 48 +/- 1 (SE) ml .min-1. kg-1; age 24 +/- 1 vs. 25 +/- 1 yr]. Daily energy intake was higher in T than in UT subjects (18,607 +/- 835 vs. 12,493 +/- 720 kJ/day, P < 0.05), reflecting a 2.3 times higher carbohydrate intake (678 +/- 34 vs. 294 +/- 18 g/day, P < 0.05). After 1 g/kg body wt glucose, C-peptide and insulin responses were lower in T than in UT subjects (P < 0.05). However, after identical relative glucose loads [high: 2.3 +/- 0.2 (T) vs. 1 (UT) g/kg; low: 1 (T) vs. 0.4 +/- 0.03 (UT) g/kg], glucose [incremental areas 300 +/- 56 (T) vs. 304 +/- 35 (UT) mM.180 min and 148 +/- 30 (T) vs. 124 +/- 22 (UT)] and C-peptide [181 +/- 18 (T) vs. 171 +/- 27 (UT) nM.180 min, and 100 +/- 13 (T) vs. 71 +/- 12 (UT)] responses did not differ between groups, while insulin responses were lower in T [at low relative load 15 +/- 4 (T) vs. 20 +/- 2 (UT) nM.180 min, P < 0.05]. The study indicates that the training-induced sparing of insulin secretion and lowering of plasma glucose concentrations are only relative to the accompanying increase in carbohydrate intake. However, training may be wholesome by increasing hepatic insulin extraction and thereby decreasing arterial insulin levels.