Intermittent Fasting for Athletes: Top 10 Things Should Know

Intermittent fasting and time-restricted eating are some of the most popular trends in dieting (second only to maybe keto or Whole 30). Research released recently in the journal Cell Metabolism suggests that eating within a 10 hour window could help metabolism and reduce the risk of heart disease (but, keep in mind that the study only researched a small sample of people, Brittany Modell, MS, RD, CDN, founder of Brittany Modell Nutrition and Wellness points out). But what about for endurance athletes—can time-restricted eating be beneficial, metabolically, and supply enough fuel for a race or training session? Dietitians weigh in with advice on intermittent fasting athletes need to know before starting a fasting routine.

RD Tips on Intermittent Fasting Athletes Should Know

1. There are a few different types of time-restricted eating.

Fasting can be done in varying degrees of hardcore. First, there is time-restricted eating, like the 16:8 method, one of the most popular forms of intermittent fasting, in which you are fasting for 16 hours and eating during only 8 hours of the day. “Technically, if you haven’t consumed anything for 8 hours, you’re fasting,” explains Alix Turoff, RD, so most people tend to fast overnight to begin with. It’s the alternate day fasting and whole day fasting that are more of a commitment and don’t typically benefit athletes’ busy training schedules or caloric needs.

2. Endurance athletes may need to fuel more frequently than the rest of the population.

Every athlete is different, but most endurance athletes actually have trouble getting enough fuel in their tanks. A 10-hour eating window (for example, 10 a.m. to 8 p.m., or 8 a.m. to 6p.m.) could work for some athletes, but for others who have late night training or early morning training and need a snack before or after, it may not. For optimal muscle building, “most of my endurance athlete clients eat every 3 to 4 hours,” says Tony Castillo, MS, RDN, LDN, nutrition consultant for RSP Nutrition. This could mean more mini meals scattered throughout the day.

3. If you are fasting, 10 hours instead of 8 hours of eating may make a difference.

The 10-hour eating window described in the above study could be slightly more advantageous for athletes than a standard 8-hour eating window. “That is 2 extra hours of fueling,” Castillo points out, and could be a whole extra meal that you get in your day.

4. Carb loading is beneficial to athletes to keep their glycogen stores up.

“Endurance athletes will generally want to carb load because consuming adequate carbohydrates will prevent chronic glycogen depletion and allow you to train at your best,” Modell says. If you start out a race or start out training with low glycogen stores in your muscles, your performance can suffer, Modell adds, so you don’t want to wait too long in between meals. When you use up a ton of glycogen, you may burn fat, but you do want to make sure you have enough fuel in your tank before and after workouts, especially for high-impact exercise.

**5. You can train on some fuel from the night before.**

With glycogen stores from the night before with enough healthy carbs, you can likely train in the morning without a problem. “As long as your glycogen stores are full, there should be enough fuel in the tank for a 60 minute workout,” Turoff says. But, if you push much past that with endurance activity, you might not have an easy time during the workout, Turoff adds.

6. Intuitive eating can have benefits for athletes.

When you’re intermittent fasting, there’s not as much room for intuitive eating, which is simply eating when you feel hungry, and stopping when you feel full, Modell says. Being on a schedule may mess with that. Modell suggests eating a pre-workout snack or mini meal to keep your blood sugar up, to make sure there’s something in your stomach, and to fuel your muscles.

7. Endurance athletes need more calories, so you’d have to cram more into less time.

Many people who try intermittent fasting do so for weight loss and preventing overindulgence, but it might not make that much sense for elite athletes who are trying to load up on calories. “If you’re cutting down the amount of time you have to eat, getting the right amount of nutrition in is going to be difficult,” Turoff says. You’ll also have to eat bigger meals in a shorter window of time, and that might not be the best for your digestion, especially before a workout.

8. If you’re doing time restricted eating, you need adequate protein intake.

Of course carb-loading is key, but you’ll also want to make sure you get enough protein to keep you full when you’re only eating within an 8, 10, or 12-hour period, says Claire Barnes, Registered Nutritionist & Advisor for Bio-Kult. The protein you eat the night before will also sustain your energy for the next day.

9. Time-restricted eating could potentially give you more time for the muscles to recover overnight.

If you’re eating all your meals within 10 hours of the day, your body and muscles, most importantly, may have more time to restore and recover overnight, Barnes says. It’s mentioned in the recent Cell Metabolism study, because some study participants claim that intermittent fasting could help you get a better night’s sleep: “84 percent of the participants demonstrated increased duration of sleep and/or increased sleep efficiency at the end of the intervention,” says Barnes. The study participants also self-reported (which could be perceived as slightly biased) more energy in the morning.

10. Your circadian rhythms (and training) might stay on track.

Scheduling your mealtimes, and your bedtime, could help regulate your circadian rhythms across the board. And regulating your circadian rhythms could help with sleep patterns, stress levels, and overall health, Barnes adds. Your workouts will stay timely too, especially if you front-load them in your day. “Aiming to undertake most of your training within the beginning of the day and within daylight hours can help improve circadian rhythms,” Barnes says.

The bottom line on intermittent fasting athletes should know:

Time-restricted eating may have metabolic benefits for weight loss, but it may not be beneficial to athletes, especially those who are trying to fuel their bodies for training with enough calories and nutrients.

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