Before changing the way you eat and altering your diet in any significant way, please speak with a health professional to make sure it's the best decision for you.
If the very thought of spending hours at a time without food spirals you into a panic, it will definitely freak you out that time-restricted eating—otherwise known as intermittent fasting—has taken off in a biiiig way over the past few years.
Yep, people have been intermittently fasting on purpose, not for religious reasons (that is, unless your religion is CrossFit), and the reported benefits of intermittent fasting include everything from improved concentration and stable blood sugar to weight loss and disease prevention.
Some fasters use the 16:8 method (fasting for 16 hours and eating during an eight-hour window), while others choose to take a full day off eating or at the very least drastically reduce their calorie intake during that day. But with such extreme calorie deprivation, what kind of impact does intermittent fasting have on exercise? To get a little insight into how fasting can help (or hurt) exercise routines, we asked five people from across the country who have all tried IF to give us their honest review.
For some, it's no food, no problem...
When Lila, a 31-year-old woman living in the Bay Area, first started intermittent fasting, she was initially worried about working out on an empty stomach. But she discovered that fasting not only helped energize her workouts in a new way but helped her lose weight. "I used to be terrified of running on an empty stomach, but I quickly found that my runs were stronger than ever," she says. "I also lost weight when I started working out at the end of my fast."
, CSCS and owner of in New York City, says that working out toward the end of your fast can not only lead to stronger workouts but can also help with the body's fat-burning process. "Since your blood isn't being diverted to digestion, it can circulate throughout the body more easily," he explains. "By exercising toward the end of your fast, your body starts using fat for fuel because glycogen levels are so low. The result? Weight loss."
Bea, a 26-year-old woman based in North Carolina, said that while working out at the end of her fast was initially tough for her, once she broke through that initial barrier, she saw amazing results.
"There's a bit of an adjustment period—I would get a little nauseated at first—but now I'm at my most energetic when I just roll out of bed and head straight to the gym," she said. "I know I'm not relying on glucose to fuel me; I'm burning fat instead. Plus, it's so much easier for me to move on an empty stomach."
Danny, a 34-year-old man living in Virginia, fasts one day a week for 24 hours. While he hasn't worked out a lot while actually on his fast, he's experienced improved overall focus, which has led to better workouts as a result. "When your mind is clear, it only makes sense that you'd have better workouts," he said. "I haven't felt a crash or significant weakness at all."
... while others had a little more of a challenge.
Of course, everyone is different, and some people find that fasting has been the exact opposite of good for their workouts.
Dean, a 30-year-old man living in New York practiced the 5:2 fasting method, meaning he ate normally five days a week and restricted his calorie intake to 600 two days a week. "My workouts the day after fast days had mixed results," he admitted. "I'd have to have a cup of coffee before each workout, and honestly, I felt sluggish and ultra-full from eating real meals. I tried to work out on a fast day once and that was utterly worthless. Frankly, I don't advise the 5:2 method for anyone, and I quit pretty quickly."
However, Dean tried the 16:8 method and found it was a lot better for his body. "It's great for CrossFit. I always feel ready to go and have enough fuel to recover," he said.
, a New York-based nutritionist, said the main thing she sees with exercise and intermittent fasting is that it's completely specific to the individual. "I wish there were a more one-size-fits all answer, but everybody is different. Some people are totally fine working out on empty stomach after waking up, and that's great."
Brown thinks experimenting with different fasting methods and foods is a great idea, and Tamir says that the key to a strong workout at the end of a fast may simply lie in what you eat for your pre-fast meal.
"Eating complex carbs prior to fasting will help you with an endurance-demanding workout by helping to keep your glycogen levels higher," he explained. "When doing more of a strength-based workout that isn't as demanding in terms of endurance, you can eat fewer carbs prior to your fast and still have an effective workout."
Rachel, a 23-year-old woman living in Chicago, was training for a marathon while intermittent fasting. She found that when she ate high-fat meals for dinner, her long morning runs were practically impossible. "I practice the 16:8 method, and I nearly gave up fasting altogether because I felt so weak while running," she said. "But then I started eating meals with more complex carbs for dinner, and it really helped. Lots of whole-wheat pasta and sweet potatoes. It was a game-changer."
Tamir's last piece of advice? Hydrate! "Fasting can cause dehydration, which can lead to a bunch of unpleasant outcomes," he said. "We get a lot of fluid from food, especially fruits and vegetables. When you don't take that into account, you can easily underestimate the amount of water you need."
At the end of the day, it's important to remember that what works for someone else may or may not work for you. If your workouts are only getting weaker as a result of fasting, try playing around with what you're eating for dinner or give a different fasting method a shot—or hey, give it up altogether! Intermittent fasting might not be the right fit for your exercise or dieting goals, and that's so OK.