Intermittent fasting may affect your exercise regimen
It is not safe to exercise strenuously on days when you are fasting, says Dr. Yancy. “If you are eating only 25 percent of your daily calories and still exercising, you will suffer on those days,” he says. Your body needs energy from glycogen stores to exercise, and if these levels are low, you will feel weak. Also, when you have low levels of glycogen, your body will break down protein (the building blocks of muscle) for fuel, resulting in muscle loss. “While it is not as difficult to exercise the day of your fast, it is difficult the day after you fast because your energy stores are depleted from fasting,” he adds. Another problem with intermittent fasting is that many people get hungry after exercising, and that can lead to breaking the fast. “Timing your meals can help you achieve weight loss and weight control, but it is important to fuel your body when you are more physically active,” says Dr. Yancy. If intermittent fasting seems too ambitious, learn the tiny diet changes that can help you lose weight.
What is intermittent fasting?
Intermittent fasting—periods of voluntary abstinence from food and drink—is a broad term that can be applied to many different practices. This type of dieting has spurred many books and received a lot of attention in the last few years, since studies (mostly in animals) have shown that it may reduce the risk for several diseases as well as promote weight loss. Additional research, including a small study of four fasting people published in Scientific Reports in 2019, suggests that intermittent fasting may also help boost metabolism.
The most popular approach to intermittent fasting is the 16/8, which requires fasting for 16 hours a day. Another version, alternate day fasting (ADF), alternates 24-hour periods of fasting (which are actually very restricted 500-calorie diets) with days of eating freely. The 5:2 approach limits fasting to just two days a week, while the Warrior Diet follows a 20-hour fast with one large meal consumed at night. “Part of the confusion with intermittent fasting lies in the lack of a definition,” says Robin Foroutan, RDN, a New York City–based registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics. “To some people, intermittent fasting means that they fast every day, while to others it means they only eat between 11am and 6pm.” Here’s everything you need to know about the Warrior Diet, another type of intermittent fasting.