Burning calories and burning fat are not the same thing. Calories from carbohydrates are burned first during a workout, because they are the most readily available form of energy. If those calories go unused, they get stored in fat cells. It takes more effort for the body to muster up stored fat to fuel workouts, meaning the metabolism is really put to work. Fitness lore also says stored body fat is most effectively burned during low-intensity workouts, because they give your body more time and energy to access the stored fat, process it, and burn it up. (High-intensity workouts use calories from carbs first.)
So, with that in mind, how does consuming calories factor into a workout plan?
A new study in the American Journal of Physiology looked into the effects of eating breakfast versus skipping breakfast before a low-intensity workout amongst 10 overweight, but generally healthy, male participants—one of the first to do so with non-athletes who resemble regular people. Researchers found that eating a substantial, 600-calorie breakfast two hours before doing the workout (walking on a treadmill for an hour) caused the men to burn slightly more calories, while fasting before the treadmill caused them to burn more fat. The male bodies weren't distracted so to speak by the calories from the recent meal, and could turn right to the fat stores for energy.
But here's the really interesting bit, as The New York Times highlighted. Fasting before working out activated genes within fat cells associated with healthier metabolisms; eating before working out did not. As the study notes, "This means that exercise in a fasted state might provoke more favorable changes in adipose tissue [fat], and this could be beneficial for health in the longterm." Which, of course, is promising, though the study is small and limited to morning workouts. Skipping breakfast is also different than a more strict regimen like intermittent fasting.
If you insist on eating a meal before working out, however, or can't accept the thought of breaking a sweat on an empty stomach, there are certain guidelines to follow. Because fat fuels low-intensity workouts, eating fat before them is the easiest way to boost energy. Healthy fats are easy to come by, and can be as simple as eating an avocado for breakfast, or cooking eggs with (real, ideally grass-fed) butter or coconut oil. Nuts are also full of healthy fat; peanut butter with banana is an option. Carbs—like oatmeal or whole grain toast—should be reserved for high-intensity workouts.
Tomorrow morning, get going—but not too intensely, and not on a full stomach.
From: Esquire US