Exercise and newer insulins: how much glucose supplement to avoid hypoglycemia?

To determine the glucose supplement required to prevent hypoglycemia during moderate-intensity exercise in Type 1 diabetic patients using newer analog insulins.

Nine subjects performed 60 min of ergocycle exercise (50% VO2max), 3 h after a standard breakfast in three different conditions. Subjects were randomly assigned to preexercise liquid glucose supplement of 0 g of glucose (0G), 15 g of glucose (15G), and 30 g of glucose (30G). Blood glucose (BG) was measured before, during, and following the exercise. All subjects used Humulin N (N) and analog insulin Humalog (Lispro). A dextrose infusion was initiated when BG fell below 5 mmol x L(-1).

There was no significant difference in the magnitude of the decrease in BG exercise-induced when comparing the three experimental conditions. However, the quantity of dextrose infused was significantly higher in the 0G (10.5 +/- 3.2 g) than in the 15G (3.5 +/- 1.8 g) or the 30G conditions (1.6 +/- 1.0 g). The addition of a glucose supplement (15G or 30G) significantly prolonged the delay before the need for dextrose infusion (31.7 +/- 7.5, 51.3 +/- 4.2, and 55.6 +/- 2.6 min; 0G, 15G, and 30G, respectively). The quantity of dextrose infusion was plotted against the three preexercise glucose supplements and a regression equation obtained. Solving this equation, a glucose supplement of 40 g was estimated in order to maintain BG levels within the normal range during and after exercise.

For 60 min of late postprandial exercise followed by 60 min of recovery, an estimated 40 g of a liquid glucose supplement, ingested 15 min prior exercise, would seem likely to help maintain safe BG levels in subjects using N-Lispro.