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  • Writer's pictureSheri Colberg, PhD

What You Eat and Drink Affects Your Exercise Performance

How well you perform (physically) when you exercise is impacted in a number of ways by the intake of macronutrients—that is, carbohydrate, fat, and protein—whether you have diabetes or not (1, 2). Performance is directly affected by your calorie intake both during an activity and when you are recovering from it. Recovery, by definition, includes the entire time between the end of your last workout or competition and the start of the next one. In many cases, you may need to modify what you eat and drink for different types of training and competition, and periodized (that is, changing over periods of timing for training vs. competition) guidelines can lead you to the appropriate type, amount, and timing of intake of macronutrients and fluids to help you perform optimally (2).

All active people can experience a relative energy imbalance resulting from a mismatch between how many calories they’re consuming and how many they’re using during exercise and recovery. Many nutritional strategies for training and competition may involve pre-event, during-event, and between-event eating to address how to adequately replace calories and fluids. In addition to these and other factors (including muscle and liver glycogen storage and use, hydration, and micronutrient and electrolyte status), individuals with diabetes are additionally impacted by their blood glucose management (see figure).

Exercise carbohydrate requirements depend on an individual’s training status for a given event, as well as on environmental and other factors. When highly trained athletes compete in higher-intensity endurance events lasting up to 3 hours, carbohydrate remains the predominant fuel for the working muscles and its availability becomes rate limiting for performance, not fat availability (3). Anecdotally, according to active insulin users with diabetes, maintenance of their blood glucose levels at more normal levels improves exercise performance (4,5). You may need to adjust both your carbohydrate/food intake and insulin doses to prevent hypoglycemia or hyperglycemia during physical activity (6, 7). Supplementing with carbohydrate remains a proven strategy to increase endurance and intermittent sports performance in individuals without diabetes (8); carbohydrate intake has the greatest impact during activities that would lead to fatigue and/or low blood glucose (9), likely by providing an alternate fuel and sparing glycogen (stored glucose) in select muscle fibers (10). Glucose uptake into active muscles primarily occurs through a contraction-mediated, insulin-independent mechanism during activity, making its use as a fuel possible even if someone is insulin resistant (11).

Although protein use as a fuel during most activities is admittedly minimal, adequate daily intake of protein, mostly during recovery, may also impact overall performance. For most regularly training individuals, daily protein requirements are roughly 1.1 to 1.5 g of protein per kg (2.2 pounds) of body weight (roughly 15% to 20% of total calories) (12). Although aging by itself increases the need for quality protein, its intake is particularly critical in strength training athletes and individuals engaging in long duration aerobic training. If you fail to take in enough daily calories, your protein needs may be increased by exercise, whether or not you have diabetes.

Adapted from Colberg SR, Nutrition and exercise performance in adults with type 1 diabetes. Canadian Journal of Diabetes, 2020 Jun 2:S1499-2671(20)30152-0 (


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12. American Dietetic A, Dietitians of C, American College of Sports M, Rodriguez NR, Di Marco NM, Langley S. American College of Sports Medicine position stand. Nutrition and athletic performance. Med Sci Sports Exerc. 2009;41(3):709-31. doi: 10.1249/MSS.0b013e31890eb86.

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