Sugary Drinks Worsen Performance

You’ve probably heard people say you need to consume sugar before a long workout to avoid glycogen depletion. A recent study suggests it depends on what kind of sugar it is.

Drinking sugary beverages before a workout is a common practice for athletes of all disciplines. The idea is that sugar will help to fuel the muscles and thus improve performance. This practice was put to the test in a recent study from the Journal of Strength and Conditioning Research.

Glycogen is a form of carbohydrate that is stored in your muscles and liver. It’s a limiting factor in anaerobic and intense aerobic exercise. In fact, when distance runners refer to “hitting the wall,” a state that makes their legs feel like they’ve been weighted down by lead, the culprit is the depletion of their glycogen stores. Glycogen depletion also reduces the body’s ability to convert macronutrients into energy.

Ensuring adequate carbohydrate intake, either before or during exercise, is one method athletes frequently use to keep their glycogen levels going strong. In the Journal study, the researchers compared two groups of athletes who consumed sugar to a control group of athletes who didn’t consume any sugar. One group consumed a drink with glucose (also called dextrose). The other group drank a beverage containing galactose, a slightly less-sweet monosaccharide. Both of those groups consumed what amounted to forty grams of sugar taken thirty minutes prior to exercise. The control beverage was sugar-free flavored water, and those athletes could not tell the difference. The control group therefore represented training in a fasted state.

Thirty minutes after consuming their drink, the athletes underwent a pretty rugged routine on an exercise bike. First, intensity was gradually increased over twenty minutes. Then, the athletes did an intense interval session. They completed the workout by maintaining a steady pace at 90% of their max power output. On average, the workout took a little over an hour to complete, which is the length of time many athletes would work out or participate in sports.

On average, glucose worsened performance compared to placebo, and galactose improved performance over placebo. This trend makes sense when we think about the difference between the two types of sugar. The body absorbs glucose rapidly, which creates a rebound effect. The resulting insulin spike leads to lower blood sugar than our initial resting values. This hypoglycemic state is likely what caused the reduction in performance. In fact, one of the athletes was more sensitive to this effect, and his time in particular was significantly decreased after drinking the glucose version.

Galactose, on the other hand, is often broken down into glucose prior to being utilized by the body. Although this tends to happen quickly, the extra step apparently creates enough of a delay that it allows for greater stability in blood sugar and a favorable condition for endurance. While there was a trend toward galactose being superior to a fasted state, it was not significant.

Ultimately, for intense exercise that lasts more than an hour, the common habit of consuming sugary beverages might be a bad idea. The relative stability of a fasted state yields greater performance, roughly similar in values to galactose. Since beverages containing galactose may be difficult to find, you’re probably safe sticking with old-fashioned cold water as your performance-enhancing beverage of choice.


1. John O’Hara, et. al., “The Effect of Pre-exercise Galactose and Glucose Ingestion on High-Intensity Endurance Cycling,Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000372

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