Exercising right after waking does deplete your energy. And since your energy stores are already depleted just from sleeping -- you burn energy-producing carbs as you snooze -- depleting your body further by working out before breakfast is a bad idea. You don't need to down a stack of pancakes before you jump on the treadmill or lift weights. But at least eat some fruit or cereal before you jock it up.
The argument for fasting cardio -- exercising on an empty stomach -- raged for a number of years in the fitness world. In theory, exercise on an empty stomach burned more fat, since your supply of carbs was depleted. Many bodybuilders and serious fitness buffs opted for no-breakfast workouts. Although the theory seemed plausible, it isn't borne out by research. As the University of Iowa Student Health website states, the difference in fat burning between the no-breakfast crowd and the breakfast crowd is small and probably not meaningful. If you work out before eating breakfast, you're likely to burn protein as well as fat, which produces muscle loss. That's not good. The Collision Sports website states: "Muscle loss is something to be avoided as much as possible."
Since your energy is depleted in the morning, especially if you exercise before breakfast, you're unlikely to work out at your normal intensity or length. Some people who exercise without eating beforehand are able to adjust to such a schedule, but others become nauseous or light-headed. Fainting is not uncommon. The University of Iowa advises students to eat something before exercising in the morning, even if it's just a piece of fruit. Fitness expert Martica Heaner, writing at the Kansas State website, says cardio fasting can put you into a state of ketosis -- where your body shifts into starvation mode -- but you might not even feel hungry. You'll have less energy and your mental focus will deteriorate.
Strategies for Cardio Fasting
Some bodybuilders believe they can counter the energy-depleting effects of cardio fasting, according to the Collision Sports website. One approach is to consume a glass of water with pinches of sea salt and trace minerals to replace the electrolytes you'll otherwise lose during cardio fasting. Another approach is to drink water with baking soda before and after a cardio fast workout to decrease post-exercise soreness. But since the benefits of cardio fasting are slim to none, according to "The New York Times," these don't seem to be worthwhile strategies.
Working out before breakfast produces no benefits and potential drawbacks, according to the "Strength and Conditioning Journal," which published a metastudy on the subject. Both non-eaters and eaters burned similar amounts of fat, and the non-eaters were likely to lose muscle and work out less intensely, leading to a reduced calorie burn compared the breakfast bunch. One study found that cyclists who cardio fasted burned protein and muscle, a detriment to performance. Another study, focusing on healthy women, concluded that those who consumed 45 grams of carbs before working out wound up eating less during the rest of the day than women who fasted before working out.
Jim Thomas has been a freelance writer since 1978. He wrote a book about professional golfers and has written magazine articles about sports, politics, legal issues, travel and business for national and Northwest publications. He received a Juris Doctor from Duke Law School and a Bachelor of Science in political science from Whitman College.