You've committed to squeezing in a workout between your commute and your desk job, but before you embark on this new regimen, you want to know: When's the best time to exercise to ensure you're getting the most out of it?
Research covered by Gretchen Reynolds in The New York Times suggests that working out early in the morning — before you've eaten breakfast — helps speed weight loss and boost energy levels by priming the body for an all-day fat burn.
The no-snooze payoff
One of the reasons working out first thing in the morning helps us lose weight — or at least protects us from gaining it — is that it pushes the body to tap into its fat reserves for fuel, as opposed to simply "burning off" our most recent snack or meal.
In one recent study, 28 young, healthy men spent six weeks eating a hefty diet of 30% more calories and 50% more fat than they had been eating before. But while some of them spent the six weeks stuffing themselves and barely exercising, the others started working out every day. Of those who worked out, half did so first thing in the morning; the other half hit the gym (and did the same workout) after a high-carb breakfast. The fasting exercisers ate the same breakfast; they just did so after working out.
At the end of the volunteers' month-and-a-half eating fest, the ones who hadn't worked out at all had, unsurprisingly, packed on the weight — about 6 pounds each. The ones who had been exercising after breakfast gained weight, too, but only about half as much.
In comparison, the people who worked out daily but hit the gym before breakfast hadn't gained any weight at all. They had been able to eat a lot of extra food — just as much as their fellow volunteers — without paying the price in additional pounds.
The study was small, short term, used a specific eating plan, and involved only men close to age 21, so it's hard to extrapolate much from the results. And the fasting exercisers didn't lose weight; they just didn't gain weight. Still, the experiment provided some of the first evidence that "early morning exercise in the fasted state is more potent than an identical amount of exercise in the fed state," the authors write.
Another smaller study helps point out why timing could be so important. In it, two groups of men ran on treadmills until they burned 400 calories (about the equivalent of a small meal, or three to four slices of toast). While one group ran on an empty stomach, the other ate a 400-calorie oatmeal breakfast about an hour before their workout.
Assistant Professor, TE