Journal Title (Medline/Pubmed accepted abbreviation): J. Sport. Sci.
Page numbers: 279-289
doi (if applicable): 10.1080/02640414.2010.531753
Type 1 diabetic patients cannot produce insulin, the hormone that signals body cells to take up glucose from the blood stream. Consequently, patients need to administer exogenous insulin with meals. Exercise can be difficult for type 1 diabetic individuals because it changes glucose metabolism and they are at risk for hypoglycemia during and/or after exercise. Both the pre-workout carbohydrate (CHO) amount and type as well as insulin dose can be altered to prevent hypoglycemia.
Isomaltulose was the carbohydrate chosen in this experiment. It has a low glycemic index (32 where pure glucose is 100) and has been shown to yield peak blood glucose levels 120 min after consumption, which is much later than most carbohydrates.
Research Question: How does the timing of consumption of a low glycemic index carbohydrate (isomaltulose) with a rapid-acting insulin dose affect carbohydrate and lipid oxidation before, during, and after endurance exercise?
Subjects:7 male type 1 diabetic subjects who exercise regularly, age 31 ± 2 y
Research design: randomized, counter-balanced
Treatment/experimental protocol: Participants arrived at the laboratory after an overnight fast. All participants administered 25% of their normal dose of fast-acting insulin and consumed 75 g of isomaltulose in 750 mL water before the exercise session. Participants rested 30, 60, 90, or 120 min between consuming the beverage and exercising. Each participant underwent each different rest period once (4 trials per subject, 7 days apart). Fifteen min before exercising, resting heart rate and respiratory parameters were recorded. Then, subjects ran on a treadmill at 71% of their previously determined VO2max for 45 min. Blood samples were acquired before the insulin/CHO administration and 0, 5, 15, 30, 60, 120, and 180 min after exercise. If a participant experienced hypoglycemia (blood [glc] ≤ 3.5 mM), 20 g of carbohydrate was administered.
Consumption of 75 g of a low glycemic index carbohydrate in conjunction with a 75% reduction in rapid-acting insulin administration 30 min before a 45 min run were effective at increasing lipid oxidation, reducing carbohydrate oxidation, and preventing hypoglycemia. This is of clinical significance because this regimen is not consistent with current recommendations regarding insulin injection before exercise. Because diabetes affects every patient differently, individuals are encouraged to talk with a physician before beginning an exercise routine or before changing insulin administration or eating habits.