The Atkins Diet May Not Be the Most Suitable for Those Looking to Increase Endurance Performance

Photo credit: BURCU ATALAY TANKUT - Getty Images
Photo credit: BURCU ATALAY TANKUT - Getty Images
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No matter how you slice it, low-carb is the diet trend du jour: The keto diet restricts your carb consumption to an almost negligible amount, a gluten-free diet—though not intentionally low-carb—forces you to look closely at your carb intake, and the Paleo diet tends to be lower in carbs since you omit sugar, grains, and processed foods. But before any of these carb-conscious eating styles became a “thing” (at least in a mainstream sense), there was the Atkins diet.

Maybe someone you know tried the Atkins diet in the 90s, or maybe you’re just hearing about it now as it resurges in popularity (about 380,000 Instagram posts now feature the hashtag #atkinsdiet). Either way, you should know this: A seriously low-carb diet could affect your performance as an endurance athlete—and not always in a good way. Here’s what to keep in mind before following this—or any—low-carb diet.

What is the Atkins diet?

Cardiologist Robert Atkins, M.D., published his book Dr. Atkins’ Diet Revolution in 1972, arguing that a low-carb diet—not the low-fat, high-carb diet popular at the time—was ideal for weight loss and heart health.

By the 90s, an updated version of the book became a bestseller as people started to question the virtues of eating low-fat-everything. The first version of the diet was essentially the Atkins 20, noted below, but a modern-day Atkins diet falls into three, more flexible categories:

● Atkins 20: Twenty grams of net carbs a day (that’s total carbs minus fiber); ideal for people with over 40 pounds to lose; the first phase is marketed as a ketogenic diet, then you gradually add more carbs over the next three phases.

● Atkins 40: Forty grams of net carbs a day; ideal for people with less than 40 pounds to lose.

● Atkins 100: One-hundred grams of net carbs a day; ideal for people who want to maintain their weight.

“For the vast majority of people, eating 40 grams of net carbs results in a fat-burning metabolism and is more sustainable for the long run,” says Colette Heimowitz, vice president of nutrition communication and education at Atkins Nutritionals, Inc., noting that Atkins research shows that this plan is conducive to weight loss and glycemic control. “Atkins 100 is meant for a lifestyle approach,” she says.

Is Atkins the same as keto?

Even though the Atkins diet is gaining more popularity alongside its low-carb cousin, the keto diet, they’re not exactly the same: A keto diet prioritizes fat in order to put your body into a state of ketosis, meaning your body produces ketones for energy, instead of relying on sugar.

That means that the macronutrient percentages of a keto diet are aggressive: about 85 percent fat, 10 percent protein, and 5 percent carbs. The Atkins diet is also low in carbs, but there’s more balance between fat and protein: Even the more aggressive Atkins 20 plan is 20 to 30 percent protein and 60 to 70 percent fat. That’s because the goal isn’t all about creating a ketone-producing state, which requires more fat; the ultimate goal is to limit carbs.

When it comes to the Atkins diet vs. keto, “overall, Atkins allows for more flexibility as we encourage people to incorporate foods back into their meals and find their carb tolerance level,” Heimowitz says.

But aren’t carbs important for endurance athletes?

Most experts still say “yep.” Camila Oliveira, a Ph.D. candidate in nutrition and metabolism at the University of Alberta in Canada, notes that several health and nutrition organizations recommend three to five grams of carbs per kilogram of body weight when training lightly or resting, and eight to 12 grams per kilogram when training more than four to five hours a day. That’s a minimum of 204 grams of carbs for a 150-pound person, twice as much as the least aggressive Atkins plan.

“Carbs are important if you’re participating in prolonged endurance training because they’re the most easily-utilized and efficient source of energy,” says Keri Glassman, R.D., founder of Nutritious Life. “Carbohydrates are stored as glycogen in your muscles, which can be tapped for energy when glucose is depleted.”

What about net carbs versus total carbs?

To be fair, the Atkins diet focuses on net carbs, which is the total carbs minus fiber, and the current recommendations don’t take this into consideration.

But even though fiber is indeed important (and suggests you’re not eating a ton of empty carb-heavy foods loaded with sugar), Oliveira notes that this concept isn’t as simple as you’d think.

“The amount of nutrients your body absorbs depends on more than just the fiber content,” she says. Other macro and micronutrients, fiber type, food consistency, and the overall health of your digestive tract also play a role. For that reason, she still suggests sticking to the carb recommendations above. “They’re evidence-based and should be safe for most athletes,” she says.

Plus, the average American only eats about 15 grams of fiber a day—and should be eating 25 to 30 grams—so it’s not like we’re talking about subtracting a ton of fiber from your total; you’d still be above the Atkins 100 threshold if you ate 204 grams of carbs, then subtracted 30 grams of fiber.

And unlike Atkins, the above recommendations are based on your body weight, which matters. “The amount of nutrients required to maintain a body of 260 pounds is very different from the amount required to a body of 130 pounds,” Oliveira says.

Are there any athletic advantages to following a low-carb diet?

Some people still love it. Heimowitz notes that Atkins brand ambassador Zach Bitter has found endurance success in the diet: He says a low-carb diet helps him avoid the highs and lows associated with carb-fueling, a common claim among keto dieters. And a Military Medicine study from 2019 shows that a ketogenic diet promotes weight loss without compromising athletic performance in military personnel. But that study was small, and the overall body of research still suggests sticking to a more carb-friendly diet for endurance performance.

“There’s currently no evidence proving that very low carbohydrate intake improves performance to a greater extent than normal carbohydrate intake,” Oliveira says. She notes a 2017 Journal of Physiology study finding that a low-carb, high-fat diet did just the opposite—and says we need more research before recommending a keto or Atkins diet to athletes.

So, should you try an Atkins diet for any other reason, and what should you keep in mind?

“The goal of the Atkins diet is to lose weight, so if your goal is to increase endurance performance, the Atkins diet may not be the most effective approach,” Glassman says.

But the diet may work for you if weight loss is your primary goal, and you try it out during your off-season (there’s a huge difference between training for an endurance event and hopping on the bike at the gym for 30 minutes). “There’s ease and clarity in being told exactly what you can eat while still enjoying a high-fat and high-protein diet,” Glassman says.

And a 2009 JAMA Internal Medicine study shows that both a low-carb/protein and a high-carb vegetarian diet can help you lose weight, so you can pick your poison (err, passion?) if dropping pounds is your main goal. Because the truth is, there are multiple ways to lose weight; the key is finding the diet that works for your lifestyle, you can stick to long term, and supports your other hobbies and workouts (say, cycling).

“Unless you have very specific athletic goals, you don’t need to stress about the numbers and grams—just include a mix of carbohydrates and protein,” Glassman says, noting that you still need to be aware of the types of foods you’re eating (i.e., don’t eat butter and steak all day). Otherwise, “experiment to see what feels best for your body.”

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