From the throwback days of high school spaghetti dinners before game day, we’ve long been trained to carbo-load before a day of physical activity. And there’s a valid reason for that: the body uses carbs more readily for fuel than other sources, like protein and healthy fats. But if you’re following a low-carb diet or they just don’t make you feel great, it can throw a wrench into training for something super intense, like a marathon. So what do you do?

“Athletes involved in endurance sports have seen benefits specifically around sustained performance for extended periods of time,” Maya Feller, MS, RD, CDN of Maya Feller Nutrition, says. However, she notes, carbo-loading is not a must.

“I had carb-loaded for six marathons when I didn’t have a clue about nutrition,” Ariane Hundt, a clinical nutritionist and trainer says. When she began training for an Ironman, she decided she didn’t want to experience the same outcomes as she had when carbo-loading for marathon training: “weight gain, muscle loss, becoming flabbier, softer, and more bloated—and slightly depressed from too many carbs affecting my blood sugar.” Fortunately, there’s a way around it.

Find out how to train for a marathon without loading up on carbs.

What happens when you cut carbs while endurance training

“Years ago, many runners thought that if they increased their carbohydrate intake in the days leading up to a big race—think breads, pasta, and rice—they would have increased energy stores, glycogen, resulting in more endurance, and decreased bonking,” Mirna Valerio, ultra-runner and Merrell ambassador, says. But she personally doesn’t eat any differently the night before a race.

Hundt is an advocate for becoming less dependent on burning carbs for fuel. “When the body becomes good at burning fat, you will lose body fat and become much less dependent on glucose from sugar and carbs as energy,” she says. “The result is that you can go for hours without food because your body uses its own stores as energy. That translates into more balanced energy, focus, being less hungry, having less cravings, and having more energy—all of which are usually affected during carb-fueled marathon training.” A fat-adapted runner, she explains, means that one’s body knows it can burn fat when carbs run low.

It’s important to take the time to train your body to get energy this way. In other words, don’t switch to a lower-carb diet and immediately go out for a two-hour run. “It’s a good idea to start marathon training season weeks one through six with shorter runs of up to an hour and a lower-carb diet to teach the body to rely on body fat as fuel,” Hundt says. “Fasted runs are a great way to teach the body to run on body fat.”

After week six, your runs should start to be longer than an hour. Hundt recommends eating a small meal with around 20 to 30 grams of carbs an hour or two before your run, and then refueling afterward with protein, veggies, and 30 to 50 grams of carbs depending on your appetite.

“Starches, such as sweet potatoes can be added to refuel glycogen stores after runs longer than two hours,” she says. “The only time that a higher carb meal won’t backfire is right after an intense workout. Any other time, a high-carb meal will create an insulin spike and fat storage.”

Here’s a sample day of eating for a fat-adapted runner, from Hundt:

• 1-hour morning run, fasted
• Post-workout smoothie with frozen cauliflower, frozen butternut squash and 20 to 30 grams of protein powder or three-egg omelette with veggies and half a sweet potato
• Lunch: Big mixed green salad with grilled chicken, half an avocado, broccoli, tomatoes, and cabbage with olive oil and lemon juice as dressing
• Afternoon snack (if hungry): One of the following: veggie smoothie, Epic bar, Raw Rev Glo Bar, or three turkey slices with half an avocado
• Dinner: Roasted salmon with grilled asparagus

Are there any carb requirements at all for long runs?

It can feel kind of jarring to go against “traditional wisdom” when it comes to carbs, especially in relation to endurance training. “Everyone’s bodies, training methods, and goals are different, so a person’s carbohydrate needs will vary,” Valerio says. 

“An average carb requirement should be based on someone’s goal body weight and duration of exercise,” Hundt says. For instance, if your goal weight is 150 pounds, then she recommends eating 100 to 150 grams of carbs per day if your workout is less than 60 minutes. For workouts longer than 60 minutes, she says you can estimate that you burn around 35 to 45 grams of carbs per hour—that’s where the aforementioned extra post-workout starchy carbs come in. (Now, why didn’t we learn this math in high school instead of calculating train collisions?)

Also, fun fact: one gram of carbs makes us retain three grams of water, Hundt says. So if you find yourself feeling bloated the morning after having sweet potatoes for dinner, that’s why.

Build in recovery days

Recovery is a crucial component of any training routine, but becomes especially important with high-intensity training. “It is important to build in enough recovery days to reduce metabolic stress, that in turn will keep your appetite in check,” Hundt says.

She notes that she was able to maintain her energy levels throughout her six months of Ironman training without destroying her metabolism without carbo-loading. She also kept her stress hormone levels in check because she made sure to take rest days, get plenty of sleep, and utilize massages, stretching, and foam-rolling as part of her recovery.

“I see the benefits of this type of training in my clients who train for endurance events and end up being fitter, lighter, and stronger as a result,” she says. 

Ready to crush those 26.2 miles? Here are the need-to-know tips from NYC’s top trainers. And if you feel like you’ve lost your running mojo, here are 6 tips for getting your runner’s high back.