Diabetes Self-Management Blog

Here at Diabetes Flashpoints, we’ve discussed how the timing of meals throughout the day may (or may not) lead to better or worse health. And while we’ve recently covered several exercise-related topics — including how comfort and other incentives can affect how often and how well you exercise — we haven’t yet explored the timing of exercise. But as a new study shows, the timing of exercise relative to breakfast may have health consequences that are worth considering.

The study, published online by the British Journal of Nutrition and carried out by researchers at the University of Glasgow in Scotland, examined 10 sedentary, overweight, mostly younger men (the average age was 28). Each participant took part in three different procedures, during different visits to the study center, designed to compare the effects of exercising before and after breakfast. The first procedure, for comparison purposes, involved not doing any exercise, then consuming a standardized breakfast provided by the study. This breakfast was tailored to each participant’s body weight, providing 5 calories per kilogram of weight (just over 2 calories per pound) and consisting of a bagel, trans-fat-free margarine, and a strawberry-flavored meal-replacement drink. Then, 3.5 hours later, participants were given a standardized buffet lunch consisting of spaghetti with meat sauce and a variety of side dishes. The second procedure involved going on an hour-long brisk walk before the breakfast, while the third procedure involved going on the walk after breakfast, with lunch still served 3.5 hours after breakfast. Participants remained at the study center for 8.5 hours at each visit, during which blood samples for a variety of measurements were taken at regular intervals.

One finding from the blood samples was that both exercise procedures resulted in an average net loss of body fat: 298 calories’ worth for exercising before breakfast, and 216 calories’ worth for exercising after breakfast. Omitting the exercise, however, resulted in an average net gain of 49 calories’ worth of body fat. Exercising before breakfast resulted in blood triglycerides that were 17% lower after 8.5 hours than without exercise, a statistically significant difference, while exercising after breakfast reduced triglycerides by only 11% — not enough to be certain the difference was not due to chance. Both exercise procedures resulted in a lower insulin response compared with no exercise, indicating that the body used the hormone more efficiently. Exercising after breakfast, however, actually lowered insulin slightly more, by 24% versus 19% for exercising before breakfast. Neither exercise procedure increased or decreased the amount of food participants ate at the buffet lunch. You can watch the lead researcher summarize the results in a video clip here.

With a sample size of 10, it would be premature to read too much about the ideal timing of exercise from this study. However, it may be worth considering that outside of a study setting, some people may find it difficult to exercise before eating anything on a given day, because of either lower motivation or actual physical difficulties. This may be especially true when attempting exercise that is more strenuous than brisk walking; without enough energy in the body, workout performance may suffer. Of course, some people have no difficulty performing grueling workouts straight out of bed, so there may be wide individual differences in willingness or ability to exercise before breakfast. For people who do exercise before breakfast, it may be especially important to remember to stay properly hydrated before and during a workout.

Do you exercise first thing in the morning, before breakfast? Why or why not? If so, do you find this routine to be relatively easy and pleasant, or does it take some commitment? Is there a tradeoff between getting exercise done early, and performing better later in the day? Does it all come down to whether someone is a “morning person”? Will you change your exercise routine based on this study? Leave a comment below!

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