When vying for weight loss, a lot of people approach their goals with a calories in, calories out mindset. Burn more calories than you eat each day, and you’ll lose weight. Burn those calories from pure, unadulterated fat, and some say that you’re golden.
That’s what makes the promise of fasted cardio so attractive. On the surface, it also makes sense: Head into your sweat session first thing in the morning before breakfast, and, since there’s no food in your system for your body to use as fuel, your body will burn the fat you’ve stored for energy instead. But that isn’t the whole story.
“Burning more fat is much different in reality than it is in theory,” says Susan Kleiner, PhD, RD, author of “Power Eating” and a sports nutrition consultant to top NFL, NBA and Olympic athletes. She points out that, apart from burning fat in the form of triglycerides floating through your bloodstream (rather than as whatever’s hanging around in your so-called trouble spots), fasted cardio often burns fewer total calories — including calories from fat — than properly fueled exercise does.
That’s because, while fasted cardio does increase the proportion of calories burned from fat during exercise, it decreases the total number of calories burned at a given rate of perceived exertion (how hard you feel that you’re working), she says. It’s important to realize that when you exercise in a fasted state, you’ll actually feel like you are working out harder, even if you’re running, biking or swimming less intensely than you would with fuel in the tank.
“It becomes physically painful to exercise in this state,” she says. “You can do it, but it’s not pretty and has never been proven to confer benefits in terms of exercise performance or intensity.”
Plus, if you’re going to get caught up in calories in versus out, it’s worth noting that research published in the International Journal of Sports Nutrition and Exercise Metabolism shows that when people eat a small snack before a cardio workout, they continue to burn significantly more calories and fat after their sweat sessions compared with those who work out while fasting.
As if that wasn’t reason enough to ditch fasted cardio for good, it’s important to remember that when you’re in a fasted state, your body doesn’t just turn to fat for extra energy. It also turns to protein. That’s right, muscle. In fact, research published in the Journal of Applied Physiology shows that an hourlong cardio workout, when performed on empty, results in up to 10% of all calories burned coming from protein — that’s about double what it would be otherwise.
YOUR PRE-CARDIO SNACK PLAN
“Weight loss doesn’t occur with under-fueled training,” Kleiner says. “It happens when you give your body what it needs to perform its best.”
To get the most fat-burning benefits from your early morning exercise, she recommends eating a small snack that combines both carbs and fat, like whole-wheat toast and a hard-boiled egg, 30 minutes to an hour before exercise. The combo will increase your workout performance and, thus, calories burned, while also helping you to build more lean, metabolism-revving muscle.
If you’re getting into hard-core or long endurance workouts lasting for more than an hour, you need to think about fueling up not just before but also during your workouts, she says. Sports drinks, gels and even raisins — when consumed during long cardio workouts — have been shown to increase performance thanks to their blend of quick-acting carbs and electrolytes.
Remember, you get out of your workouts what you put in — and that requires proper fuel.