Best Time of Day for Exercise

by Carole Jackson, Bottom Line Health

Are you a person who likes to roll out of bed and hit the gym… or the pool, the track or the tennis court — or do you prefer an afternoon or evening workout? Exercise however you like, but according to a new study, you might want to put some planning into when you work out. Belgian researchers found that exercising before eating — on an empty stomach, something most people have only first thing in the morning or late afternoon — has several beneficial effects, including preventing weight gain and warding off a truly serious disease.

An Unusual Study — They Ate Junk Food

In the study, 27 healthy young men ate a horrible diet high in sugar, fat and calories — chosen because it was just about guaranteed to create both weight gain and a reduction in the body’s ability to process blood sugar effectively.

The Belgian men were divided into three groups. The control group had to eat the awful diet and avoid exercising. Men in the second and third groups — in addition to eating the same unhealthful diet — both exercised, performing the same workout. But the second group did it soon after breakfast and the third group did it before breakfast, exercising on an empty stomach.

How Did That Work For Them?

The results were surprising and dramatic. As one might expect, the control group (the one that simply pigged out) gained a lot of weight and also saw their ability to control blood sugar (insulin sensitivity) plunge. The “exercise after eating” group also gained weight, but not nearly as much as the control group. Their insulin sensitivity also went down, just as it did in the control group.

But the “exercise before eating” group was a whole different story. Despite eating the terrible diet, this group did not gain weight… not only that, their insulin sensitivity didn’t fall, so even their bad diet did not make them insulin resistant. A breakthrough finding? You bet. As the authors said, “This study for the first time shows that fasted (empty stomach) training is more potent than ‘fed training’ to facilitate adaptations in muscle and to improve glucose tolerance and insulin sensitivity… ”

So Don’t Eat First?

Should you forgo eating before working out? Not necessarily — it depends on your goals. I consulted exercise physiologist Liz Neporent, MS, CSCS, who serves emeritus on the executive board of the American Council on Exercise and is author of Fitness for Dummies. She said that people whose interest is in heightening their performance — who are, for instance, training for an upcoming event — might do better to eat first, since they’ll need energy to push themselves harder and harder. But, she added, if it’s weight loss or maintaining general fitness that you are after, “evidence does seem to be trending toward not eating before working out.” The benefit of the before-breakfast interval is that most of the food consumed the day before is well through the small intestine and thus the inflow of nutrients is at its ebb, but you can also benefit by being sure to work out as long after eating as possible — say, just before lunch or just before dinner.

One caveat — if you find that exercising on an empty stomach makes you feel dizzy or faint, this may not be a good approach for a vigorous workout. You might find that endurance training, where you focus on low-stress repetitive actions such as mild-to-moderate spinning, can produce benefit without driving blood sugar too low. Or you may need to have a small, healthful snack that includes protein before you do any exercising. While you won’t get the same benefits as exercising on an empty stomach, the fact that you’re exercising is still a good thing!


Liz Neporent, MS, CSCS, exercise physiologist based in New York City and author of Fitness for Dummies (Wiley) and Weight Training for Dummies (Wiley). She is a contributor to ABC National News and serves emeritus on the executive board of the American Council on Exercise.