Exercising While Fasting
Can you engage in a short-term fast and exercise at the same time? Here’s what our experts had to say.
Think intermittent fasting and exercise are mutually exclusive? Not necessarily, say fitness experts and fasting advocates. Combining a workout routine with intermittent fasting is mostly a matter of common sense.
First, consider your goals. Are you exercising to burn fat or to enhance your performance? If it’s the former, says fitness guru and Eat Stop Eat (Strength Works, 2012) author Brad Pilon, “training in a fasted state creates a metabolic profile that favors extra fat burning.”
Translation? Do your Zumba class at the end of a 16-hour fast, and your body will delve into fat stores more quickly than if you down an energy bar on the way to class. That’s because our bodies first burn through easy-to-access carbohydrates and then turn to harder-to-retrieve fat stores. Near the end of a fast, your body will already be in the fat-burning phase.
The only problem? Experts suspect that we imperceptibly compensate for that extra fat burning by eating slightly more throughout the day, or by not getting up from your desk, for example, quite as frequently after a fasted workout. “Exercising while fasting tends to be one of those things that works exceptionally well in theory,” Pilon notes. “But, when the human factor gets involved, it’s a bit of a wash for most people.”
The answer, experts say, is to experiment. For some, a light workout during a fast is refreshing. For others, it’s so exhausting they give up on the eating pattern altogether. So, bring in the common-sense element: Keep notes on your workouts, and include the time of day and what you ate beforehand, Pilon advises. Rank each workout on a scale of 1 to 10. Most likely, you’ll notice a trend. Schedule your fasts and workouts during the time frames when you’ve noted the most 8s, 9s, and 10s. You may be surprised at what you find.
“Most people I’m talking to report that their workouts are better when fasted, but some do prefer to exercise after they’ve eaten,” Pilon says.
There’s no denying the psychological component. If you’re well into a short-term fasting routine and love the results, you might be predisposed to hit your stride with a workout timed just before the end of a fast. “It really comes down to comfort level,” Pilon says.
Strength coach John Romaniello, founder of Roman Fitness Systems and author of the upcoming book Engineering the Alpha (HarperOne, 2013), is someone who prefers training on an empty stomach. “If I eat anything prior to a workout, I get nauseous,” he says. “There are tons of anecdotal reports that generally find people feel stronger and have more endurance when their body is fasted and not having to break down nutrients.”
How exactly does a workout fit into an intermittent schedule? Although one of the benefits of intermittent eating is its flexibility, most people aim to end their workouts and fasts at the same time. If you’re fasting from 10 p.m. until 2 p.m., for example, hit the gym at 1 p.m. And be aware that the first meal following a fast can be the hardest to control, says Romaniello, especially if weight loss is one of your goals.
If your overall goal is more about enhancing your fitness performance — say, shaving a few minutes from your running time — you might want to consider a more comprehensive strategy to incorporate the benefits of intermittent fasting into your race-day plan.
Say your current fitness nutrition involves an array of gels, bars and sports drinks. Intermittent fasting could help your body use fat for fuel more efficiently, allowing you to simplify your race-day eating habits and focus on that personal record.
In fact, before companies started touting the benefits of “scientifically formulated” sports drinks, runners didn’t worry much about liquid nutrition during races. A slew of recent studies shows that the benefits of sports drinks have been largely overhyped: The medical journal BMJ (formerly named the British Medical Journal) recently published several articles on the topic, revealing that many of the scientists who tout the benefits of sports drinks are sponsored by sports-drink companies.
Walk into any health club today, however, and you’ll see the number of people with gallons of neon-colored sports drinks next to their treadmills, convinced it will help them train better. Instead of gulping lemon-lime electrolytes while training, strength and conditioning specialist Mike T. Nelson, MS, CSCS, who is doing doctoral research at the University of Minnesota in kinesiology (exercise science), suggests fasting: “It’s one way to lower your insulin levels so you can more easily use fat as an energy source. Even a lean person has a lot of excess energy in the form of stored fat.”
Your body needs to gradually adapt to using fat as your fuel source, so before your big race, do a couple of runs a week the morning after an overnight fast, and then gradually work up to a 24-hour fast. The process could take 10 to 12 weeks. Track your distance, time and calories consumed, and you should start seeing a trend. Nelson says: “If you can run the same distance at the same or better time on fewer calories, you are getting better at using fat without sacrificing performance.”
About 36 to 48 hours before the race, start adding in carbs. Then, on race day, you have the best of both worlds: Your body is tuned to run on fats much more efficiently and you can add carbs as needed — for a surge toward the finish, for example, or for more demanding portions such as hills.
“Trust me, come race day, your digestive system will thank you,” Nelson says, adding that many fitness enthusiasts tend to experience intestinal distress when it comes to the various sports gels on the market.