Compared to males, females oxidize proportionately more fat and less carbohydrate during endurance exercise performed in the fasted state. This study was designed to test the hypothesis that there may also be gender differences in exogenous carbohydrate (CHOexo) oxidation during exercise. Healthy, young males (n = 7) and females (n = 7) each completed 2 exercise trials (90 min cycle ergometry at 60% VO2peak), 1 week apart. Females were eumenorrheic and were tested in the midfollicular phase of their menstrual cycle. Subjects drank intermittently either 8% CHOexo (1 g glucose · kg · h−1) enriched with U-13C glucose or an artificially sweetened placebo during the trial. Whole-body substrate oxidation was determined from RER, urinary urea excretion, and the ratio of 13C:12C in expired gas during the final 60 min of exercise. During the placebo trial, fat oxidation was higher in females than in males (0.42 · 0.07 vs. 0.32 · 0.09 g · min−1 · kg LBM–1 × 10–2) at 30 min of exercise (p < .05). When averaged over the final 60 min of exercise, the relative proportions of fat, total carbohydrate, and protein were similar between groups. During CHOexo ingestion, both the ratio of 13C:12C in expired gas (p < .05) and the proportion of energy derived from CHOexo relative to LBM (p < .05) were higher in females compared to males at 75- and 90-min exercise. When averaged over the final 60 min of exercise, the percentage of CHOexo to the total energy contribution tended to be higher in females (14.3 · 1.2%) than in males (11.2 · 1.2%; p = .09). The reduction in endogenous CHO oxidation with CHOexo intake was also greater in females (12.9 · 3.1%) than in males (5.1 · 2.0%; p = .05). Compared to males, females may oxidize a greater relative proportion of CHOexo during endurance exercise which, in turn, may spare more endogenous fuel. Based on these observations, ingested carbohydrate may be a particularly beneficial source of fuel during endurance exercise for females.
Michael C. Riddell, Sara L. Partington, Nicole Stupka, David Armstrong, C. Rennie, and Mark A. Tarnopolsky
Michael C. Riddell, Oded Bar-Or, Beatriz V. Ayub, Randolph E. Calvert, and George J.F. Heigenhauser
There are currently no guidelines regarding the carbohydrate (CHO) dosage required to prevent exercise-induced hypoglycemia in children with insulin-dependent diabetes mellitus (IDDM). To prevent hypoglycemia by matching glucose ingestion with total-CHO utilization, 20 adolescents with IDDM attended 2 trials: control (CT; drinking water) and glucose (GT; drinking 6-8% glucose). Participants performed 60 min of moderate-intensity cycling 100 min after insulin injection and breakfast. CT's total-CHO utilization during exercise was determined using indirect calorimetry. In GT, participants ingested glucose in the amount equal to total CHO utilization in the CT. A total of 9 participants had BG <4.0 mmol/L in CT compared to 3 in GT (p < .05). In conclusion, glucose ingestion equal to total-CHO utilization attenuates the drop in blood glucose and reduces the likelihood of hypoglycemia during exercise in adolescents with IDDM.
Jennifer L Kuk, Shahnaz Davachi, Andrea M. Kriska, Michael C. Riddell, and Edward W. Gregg
This article briefly summarizes the “Pre-Diabetes Detection and Intervention Symposium” that described ongoing and past pre-diabetes interventions, and outlined some considerations when deciding to target specific populations with pre-diabetes. The success of type 2 diabetes (T2D) prevention clinical trials provides clear evidence that healthy lifestyle change can prevent the development of T2D in a cost effective manner in high risk individuals. However, who to target and what cut-points should be used to identify individuals who would qualify for these T2D prevention programs are not simple questions. More stringent cut-offs are more efficient in preventing T2D, but less equitable. Interventions will likely need to be adapted and made more economical for local communities and health care centers if they are to be adopted universally. Further, they may need to be adapted to meet the specific needs of certain high-risk populations such as ethnic minorities. The Chronic Disease Management & Prevention Program for Diverse Populations in Alberta and the Pre-diabetes Detection and Physical Activity Intervention Delivery project in Toronto represent 2 examples of specialized interventions that are targeted at certain high risk populations. To reverse the current T2D trends will require continued efforts to develop and refine T2D prevention interventions.