Intermittent fasting is a fitness craze that involves not cutting calories, but getting an adequate amount of calories in within a smaller window of time, for example, from noon to 8 p.m. There are many ways to do it, and the most common way is to go 16 hours fasted and then eat meals only within the next eight hours. The question is, is intermittent fasting safe for runners?

Melissa Piercell, a Toronto-based naturopath, says that for most runners, intermittent fasting should be fine. “Back in the seventies, the idea was to get in three square meals a day. People thought that eating well meant eating those three meals a day.”

She continues, “In the nineties, we started doing six small meals a day. And as we do, those six small meals became six big meals.”

Piercell explains that snacking helps balance blood sugar and helps prevent hypoglycemia, but it makes our bodies very dependent on eating every three hours. When blood sugar goes down, bad things happen. However, we’ve arguably swung too far the other way, and become so dependent on this constant stream of fuel that we don’t tap into the stored fuel. One of the reasons that we don’t tap into stored fuel very well is because we’re constantly snacking. Your body will first use the easy-to-digest carbs as energy. Those are things like bread, oats and fruit. 

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Introducing fasting can encourage runners to use their stored energy, or fat, as fuel and even encourage weight loss. 

In terms of how this eating regimen applies to runners, Piercell doesn’t suggest intermittent fasting for elite runners, but rather recommends implementation for a more recreational runner. She does also stress the need to remember adequate recovery. “You have to time your runs for when you’re eating. As long as your exercise is timed appropriately, intermittent fasting should be fine. However if you’re an exercise first-thing runner, and you don’t plan to eat until noon, you won’t recover as well.”

The studies Piercell has seen so far suggest that intermittent fasting can help maintain blood glucose levels and prevent energy crashes. She explains, “When your body is used to going longer without food, you’re less likely to crash and reach for something sugary.” She cautions that the only people who shouldn’t intermittent-fast are people with diabetes. 

For people new to endurance athletics, it’s recommended to begin fueled for your workouts before introducing fasted or depleted exercise. 

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