Eating During Exercise

By Jenny Ives Dietitian - PCC Athlete and Associate

Ideally, during exercise that last longer than 60 minutes, you should try to balance your water and energy output with enough fluid to match your sweat losses and enough carbohydrate intake to provide energy and maintain normal blood sugar. You can significantly increase your stamina by consuming about 100 to 250 calories (approx 25-60 grams) of carbohydrates per hour while performing endurance exercise after the first hour (ACSM 2000). The most recent research involving cyclists indicates that sports beans, sports drinks, and gels all offer performance benefits (Campbell et al 2007)

Better yet, it is wise to mix up your foods and fluids so that you are getting a variety of types of carbohydrates. For an example instead of just a sports drink, choose a sports drink and a banana or part of an energy bar and extra water. This stands behind the fact that different sugars use different transporters resulting in an increased absorption of carbohydrates giving you more fuel to support your exercise. Engineered sports foods commonly contain 1-2 types of sugars, so ideally if you can physically handle a variety of energy products and natural foods than you may want to experiment.

A moderate to hard endurance workout often supplies about 50 % of the energy. And as you deplete carbohydrates from muscle glycogen stores you rely more so on blood sugar for energy. Therefore by consuming carbohydrates during exercise, such as gels, sports drinks, etc your muscle have an added fuel source. As we know, much of our performance depends on mental stamina, for that reason is wise to maintain normal blood sugar levels to keep your brain fueled and help you think clearly, concentrate, and remain focused. Your body really doesn’t’ care if you ingest solid or liquid carbohydrates both are seen to be equally effective, it’s sort of a matter of what you personally do best with. Some people prefer the natural sugars from fruits and juices, while other choose energy gels and bars, or sports drinks and hard candy. It’s up to you to experiment and find the foods that work best for you. An avid cyclist in England that I have had the honor to work with gets through his races with Kendal mint cake (380 calories, 0 grams protein, 95 grams of carbohydrates).

The question that remains; are more carbohydrates better? The answer to this is no, if you consume more carbohydrates than you need than it just sits in your stomach which can lead to other issues. In a study of well trained women cyclist, who did two hours of moderately hard endurance cycling while taking in a beverage that provided 60 grams (240 calories) of glucose per hour resulted in the highest amount of carbohydrate being used. However, when the women consumed a beverage with 90 grams of glucose (360 calories) per hour there were no change in performance. This is most likely because the excess fuel intake sat in the stomach unabsorbed leading to gastrointestinal discomfort. With the 60 gram intake there very few complaints of stomach distress and with plain water there was only one complaint (Wallis et al 2007). A later study has shown that when the women consumed a variety of carbohydrates there was even fewer complaints.

Keep in mind that excess sugar or food consumed at once can decrease the rate at which fluids leave the stomach and become available to replace sweat losses. Therefore be conservative with your sugars during intense workouts and hot weather, when fluid replacements becomes more important than carbohydrates. When the cold weather workouts roll in the risks of dehydration are greatly decreased therefore sugar fixes can provide much needed energy.

Lastly, if you are not used to consuming 100-250 calories per hour than you need to practice eating during training to figure out which foods and fluids work for you. As always if you want to try something a new drink, bar, gel, etc be sure to do it during training and not on race day. Then once you try something keep a list of what works and what does, however keep note of the temperature. For instance you may not do well with a peanut butter and jelly sandwich in 90 degree weather, but it may be just fine in 40 or 50 degree weather. Do be afraid to try new foods after all eating the same foods every workout gets awfully old.