Is it better to exercise before or after breakfast?

Adam's Journal

I like to exercise right after I wake up, before eating anything. Meanwhile, my girlfriend, Mary, enjoys an energy bar each morning before her workout.

Is one of us doing it wrong? Is there any advantage to eating before a workout versus after one?

Dr. Prescott Prescribes

This past spring, a study found that fit young men consumed considerably less each day when they worked out before eating anything than another group of fit, young men who ate breakfast, then worked out. The workout-before-breakfast groups ended up running an overall deficit of about 400 calories each day, while those who ate before hitting the gym ended up consuming almost 500 calories more than they burned throughout the day.

Previous research also has suggested that exercising before breakfast leads the body to burn a higher percentage of fat for fuel during vigorous exercise, instead of relying primarily on carbohydrates. Subjects who worked out before breakfast seemed better protected against weight gain and insulin resistance, a predictor of diabetes, than those who ate before exercising.

Physiologically, a 2017 study determined that exercising before breakfast resulted in higher activity levels in genes that improve blood sugar regulation and are associated with improved metabolic health. On the flip side, the research found that fasting subjects actually burned slightly fewer calories during their workouts than those who'd consumed breakfast beforehand.

So, what does this all tell us?

These were all limited, short-term studies, which means that it can be difficult to extrapolate to form broader conclusions. Still, on balance, if I had to choose a “side,” it looks like there may be slight longterm advantages to the exercise-first approach.

That said, working out on an empty stomach means you'll have low blood sugar levels, which may negatively impact your performance during that workout. It also may leave you feeling depleted during that exercise session, as freshly consumed carbohydrates are the most efficient source of fuel for working muscles.

All told, it comes down to personal preference. As long as both Mary and you are working out regularly, you're both winners!