Glycemic responses to exercise in IDDM after simple and complex carbohydrate supplementation

Subjects with IDDM should take carbohydrate before exercise to avoid hypoglycemia. However, there is little information on the glycemic effect of recommended supplementation. This study is aimed to determine the glycemic effects of oral glucose or bread (30 g carbohydrate) before 45 min of moderate exercise.

Nine subjects with uncomplicated IDDM did 45 min of bicycle ergometer exercise at 60% VO2max in the morning before insulin injection on three occasions: 1) with no carbohydrate supplement, 2) with 30 g glucose in water at -5 min, and 3) with 30 g carbohydrate as white bread with water at -20 min. The glycemic responses were determined. The glycemic responses to glucose and bread were also determined without exercise in six subjects.

Without carbohydrate, exercise caused a small fall (-1.2 +/- 0.6 mmol/l, mean +/- SE) in plasma glucose (PG). With either glucose or bread, PG rose (the change in plasma glucose relative to basal [delta PG] = 5.1 +/- 0.8 and 2.6 +/- 0.8, respectively). The rise was greater (P < 0.01) without exercise (delta PG = 6.9 +/- 0.7 and 4.5 +/- 0.7, respectively). During exercise, glucose increased PG levels more than bread increased glucose levels P < 0.05).

Before morning insulin injection, the fall in PG during moderate exercise in IDDM subjects is generally small or absent. The glycemic effects of complex carbohydrate are slightly less than glucose before exercise. Under these circumstances, the usually recommended amount of carbohydrate tends to cause an unwanted elevation of PG; thus, IDDM subjects should anticipate reducing or even omitting carbohydrate supplementation after monitoring their individual glycemic response.