Abstract
Low glycemic index (GI) foods may confer an advantage when eaten before prolonged
strenuous exercise by providing a slow-release source of glucose to the blood without
an accompanying insulin surge. To test this hypothesis, eight trained cyclists pedalled
to exhaustion one hour after ingestion of equal carbohydrate portions of four test
meals: lentils, a low GI food (LGI); potato, a high GI food (HGI), and glucose and
water. Plasma glucose and insulin levels were lower after LGI than after HGI from
30 to 60 min after ingestion (p < 0.05). Plasma free fatty acid (FFA) levels were
highest after water (p < 0.05) followed by LGI and then glucose and HGI. From 45 to
60 min after ingestion, plasma lactate was higher in the HGI trial than in the LGI
trial (p < 0.05) and remained higher throughout the period of exercise. The rank order
from lowest to highest for total carbohydrate oxidation during exercise was water,
lentils, glucose and potato. Endurance time was 20 min longer after LGI than after
HGI (p < 0.05). These findings suggest that a low GI pre-game meal may prolong endurance
during strenuous exercise by inducing less postprandial hyperglycemia and hyperinsulinemia,
lower levels of plasma lactate before and during exercise, and by maintaining plasma
glucose and FFA at higher levels during critical periods of exercise.
Key words
Glycemic index - exercise - carbohydrates - glucose - insulin - free fatty acids -
lactate
