Atkins for Endurance Runs: Why Cutting Carbs Eliminates Tummy Troubles and Powers You for Hours

Running a marathon is serious business, which is why most competitive runners have an unflagging game face. (After all, any extra effort—like that needed to muster up a smile—might zap important energy stores!) But it’s hard not to grin when you get a look at the ridiculous signs held by fans, many of which refer to the gross things that can happen during long distance runs. All those banners about diarrhea and going number 2 while running down a crowded street? Well, they’re funny because they’re true.


However, stomach cramps, sprints to the port-potties, and worse don’t actually need to be a part of your marathon plan, according to Colette Heimowitz, MS, VP of Nutrition and Education at Atkins.

“Carb loading for cardio endurance can help you have energy, but it has side-effects,” says Heimowitz. “You have to take in so many carbs right before an event that runners get so many to intestinal upsets.” Even worse, she says, most runners who rely on carbs for their energy tap their stores well before end. 

When I spoke with Heimowitz last week, a few days after the 2022 Boston Marathon, I wasn’t surprised to hear her push for fewer carbs. (She works for Atkins after all.) But I was surprised to hear that her idea of a healthy pre-marathon meal was to focus on fat more than on protein. Her reasoning: Our bodies are equipped to burn two source of food: Carbs and fat. Carbs are a simpler source of energy which is one reason the body will burn them first. However, fat is a more sustainable source of fuel—we have more of it in reserve which means we can go a lot longer without needing to replenish it. (Plus getting rid of the extra carbs will help settle the stomach, making tummy troubles a thing of the past.)

The idea is to get the body burning fat even before the race starts. To that end, her ideal pre-race meal would include foods with healthy fats such as avocados, nuts, seeds, beans, salmon, and Greek yogurt. (Per Heimowitz, you can eat meat, however it’s not necessary.) But, eating just one meal that’s low in carbs and high in fat isn’t enough to completely switch how your body gets its fuel: Your body goes through an adaptation phase when it shifts from burning carbs to burning fat which is why so many runners look like they’re out of gas when their carb stores run out—it takes time for the fat-burning to kick in. Ideally, says Heimowitz, you’ll make this change to a lower carb, higher healthy fat diet at least 4 weeks before a big race so that your body is used to running on all cylinders with this new type of fuel.

 Image via Runner’s World


Also Read:

How to Survive an Ultra Marathon

Your Guide to Good and Bad Fats

Coconut Oil vs. Olive Oil: Which Healthy Fat Should You Cook With?

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