Glycemic response to carbohydrate and the effects of exercise and protein
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Objective The purpose of this study was to investigate the effects of pre-exercise and protein coingestion on the glycemic response to carbohydrates. Methods Twenty-one volunteers (13 males and 8 females) aged 22 y (ᠳ.8 y) participated in four trials in random order. These included: 1) glucose ingestion at rest (RG), 2) glucose and protein ingestion at rest (RGP), 3) glucose ingestion after exercise (EG), and 4) glucose and protein ingestion after exercise (EGP). Exercise consisted of 45 min of cycling at 60% of participants' age-predicted maximum heart rate. Test drinks contained 50 g glucose or 50 g glucose with 20 g whey protein. Venous blood samples were taken at baseline and subsequently every 15 min for 2 h after drink consumption. Blood plasma was subsequently analyzed for glucose and insulin. Results Plasma glucose concentration was significantly lower in the RGP group than in the RG group at 30, 45, 60, and 75 min and in the EGP group than in the EG group at 30, 45, and 60 min (P < 0.05). Plasma insulin area under the curve was significantly higher in the RGP group than in the RG group and in than in the EGP group than in the EG group (P < 0.05). No significant effect of exercise was seen on glycemic or insulinemic responses. Conclusions Coingestion of protein with carbohydrate reduces glycemic response and increases insulinemic response in healthy subjects, whereas pre-exercise seems to have no effect.
Clinical and Sports Nutrition