Carbohydrates Are a Fuel, Not a Foe

In this era of chicken-based chips and protein-infused seltzer, the importance of protein is now top-of-mind. We’ve understood that avocado and nuts can offer the “good” type of fat. But the third macronutrient, carbohydrates, is often still demonized, in part due to diet trends, but also a fundamental misunderstanding of their function.

The mention of carbs might make you think of a basket of bread rolls, a bowl of white rice, or a bag of potato chips. But carbs are present in four of the five major food groups: fruit, vegetables, whole grains, and dairy. You can’t avoid them, and experts say you shouldn’t.

For most people, high-quality carbs can be part of a healthy daily diet, providing energy, fiber, vitamins, minerals, and beneficial plant compounds. The source, degree of processing, portion size, and timing determine the impact of carbs on the body. 

In this article, you’ll learn how elite athletes deploy (not avoid) different types of carbs, to help you figure out what works best for your own routine and activity level. 

Certain diseases and conditions require careful monitoring of carbohydrate intake, such as diabetes and celiac disease. Before making any major dietary changes, consult with your physician. 

The role of carbohydrates

Carbohydrates are broken down into glucose, the main source of fuel for your brain under typical dietary conditions. At rest and during lower-intensity activity, your body generally uses a mixture of fat and glucose. As exercise intensity increases, it relies progressively more on glucose from the bloodstream and glycogen stored in the muscles.

When you consume carbohydrates, some glucose is used immediately, while excess glucose can be stored as glycogen for later use, primarily in skeletal muscle and the liver. This is why you’ve probably heard of runners “carb-loading” the days before a long race—to keep the energy stores full and delay fatigue.

“Carbs support everyday movement and physical activity,” says Christina Schreckengaust, a registered dietitian and board-certified specialist in sports dietetics at the Atria Health and Research Institute. After exercise, carbohydrates replenish glycogen stores in the muscle and liver. 

For regular exercisers, properly timed carbs can be the difference between finishing that half-marathon instead of hitting a mental and physical barrier thought to be caused by depleted muscle glycogen stores. Even with shorter bouts of cardio—like a half-marathon, but even a 5K—limited carbohydrate intake can be counter-productive to performance, recovery, and overall health.

Low-carb diets are also counterproductive for building muscle, Schreckengaust notes.

Not getting enough carbs while lifting regularly will leave gains on the table. Meals with carbs and protein will allow the body to use carbs for recovery, while the protein is spared for its primary job: building muscle. 

The type of carbs matter

Simple carbs

Simple carbs are a must for athletes, particularly those involved with endurance sports. Simple carbs, like those found in table sugar, honey, fruit juice, and many highly processed foods, are digested quickly, and can rapidly raise blood sugar.

These properties make them a great “quick carb” when athletes need an immediate fuel that won’t sit in the stomach for long periods of time. While these types of carbohydrates shouldn’t be a majority portion of regular meals, they play an important role. 

“If I'm working with an athlete training for a race, we will discuss quick carbs before and during the event,” Schreckengaust said.

Simple carbs are often thought of as the “bad” carb, but they have their time, place, and proportion. Fruits, which contain fructose, and dairy products, which contain lactose, are also simple carbs, for instance, but they also contain water, antioxidants, vitamins, and minerals that contribute to a healthy diet.

Complex carbs 

Complex carbs contain longer chains of carbohydrate molecules, which take longer for your body to digest and increase your blood sugar more slowly. However, some refined complex carbs, like white bread, white rice, and some breakfast cereals, have been stripped of fiber—and the body quickly digests them like a simple carb.

Examples of unrefined complex carbs include oats, brown rice, quinoa, beans, lentils, starchy vegetables, and whole grain breads. (Sourdough bread, while often made with white flour, has a bit more protein per slice and typically has a lower glycemic index than processed white bread due to the fermentation process.)

Most daily carb intake should come from fiber-dense, nutrient-rich complex carbohydrates, says Schreckengaust. To keep meals balanced, she recommends the visual "Plate Method": fill 50% of your plate with non-starchy vegetables, 25% with lean protein, and 25% with high-fiber, minimally processed carbohydrates, adding healthy fats like olive oil or avocado in smaller portions. She adds that you don't need to be overly restrictive or avoid quick-digesting carbs at all costs.

When considering cardiovascular health, Dr. Alon Gitig, Director of Preventive Cardiology at the Atria Health and Research Institute, recommends carbohydrates that contain fiber, like fruit and whole grains. They’re absorbed differently than the same amount of sugar contained in something like juice or honey. The fiber slows the digestion and absorption of the sugar, leading to a less pronounced spike in blood sugar. These slower-digesting carbs also tend to be more satiating, which is important for weight management—a key component in preventive cardiovascular medicine. 

These slower-digesting carbs also tend to be more satiating, which is important for weight management—a key component in preventive cardiovascular medicine. These foods may also support brain health, according to Dr. David Dodick, Chief Science and Medical Officer at the Atria Health and Research Institute. Diets rich in fruits, vegetables, legumes, and whole grains are associated with better cardiovascular and metabolic health, both important for preserving cognitive function. Their fiber, micronutrients, and bioactive compounds may also influence inflammation and the gut microbiome, although the precise mechanisms linking these foods to long-term brain health remain under investigation.

What determines your carb needs

In general, the recommended daily allowance for carbs is 130 grams per day for brain function, fiber, vitamins, and mineral needs. From a sports nutrition standpoint, the longer you exercise, the greater the need, Schreckengaust says. 

She tailors her recommendations for the individual, but it follows a general guideline:

• Light activity/recovery days: 3-5 grams carbohydrate per kilogram of body weight. Example: for a 160 pound person, about 217-360 grams per day.
• Moderate training (~1 hour/day): 5-7 g/kg bodyweight.
  Example: for a 160 pound person, about 360-500 grams per day.
• Endurance training (1-3 hours/day): 6-10 g/kg bodyweight.
  Example: for a 160 pound person, about 435-725 grams per day.
• High volume/endurance training (3+ hours/day): 8-12 g/kg bodyweight.
  Example: for a 160 pound person, about 580 and 870 grams per day.

These requirements are highly dependent on the sport. For example, a recreational walker and a triathlete have very different carb demands. To illustrate how carbohydrate needs change, Schreckengaust provides an example (see our chart below) of someone at a high-volume and recreational activity level.

Carbs affect performance and performance affects carbs

Carbohydrates don’t just fuel your exercise. Regular exercise can also change how your body responds to carbohydrates. “Studies clearly demonstrate that even relatively short stretches of regular cardio exercise can improve the muscle’s responsiveness to insulin’s signal,” says Dr. Gitig.

That means regular cardio sessions, even in the short “exercise snack” format, can make your body more tolerant to consuming carbs without spiking blood sugar levels. (Read more about microdosing movement here.) Resistance training, like weightlifting, can also improve your body’s tolerance for carbs, Dr. Gitig notes. In fact, resistance training increases the total amount of muscle cells available to remove glucose from the bloodstream, while also improving the individual cell’s ability to clear glucose. 

What happens when you underfuel?

For serious athletes, skimping on carbs can have serious detrimental effects. Workouts will feel more difficult, you will fatigue earlier, and you will find yourself unable to sustain high-intensity performance. You can also expect slower recovery, Schreckengaust says. 

An endurance athlete herself, Schreckengaust is well aware of the dangers of underfueling. Fatigue and low energy stores can be extremely harmful, particularly during a race, she says. ”You can hurt yourself, especially if you're on a bike, or even running.”

If you’re chronically underfueling, it can also lead to Relative Energy Deficiency in Sport (REDS), an endocrine and metabolic-disrupting syndrome that negatively affects bone health, and impacts both men and women. This is true for people at various performance levels.

Common carb misconceptions to be aware of

Schreckengaust shares some common misconceptions that she still hears regularly along with actionable, more accurate information.

“All carbs are bad.” Many people are still stuck on the oversimplification of carbs = bad. They’re not, but it can be deceptively easy to overdo it. “For example, one serving of pasta is 1/3-1/2 cup, depending on the size of the pasta. If your fist is roughly the size of 1 cup, it's not a lot of pasta, which means you can easily consume more servings.” 

“Fruit and dairy have too much sugar.” The carbs in whole fruit contain fiber, vitamins, minerals, water, and phytonutrients—which are an essential part of a balanced diet. Dairy contains calcium and protein. There is so much additional value to these foods, says Schreckengaust, and should not be eliminated altogether. 

“I want to lose weight. I’m cutting carbs.” Schreckengaust cautions that it can kick off a vicious cycle. She gives the example of a busy, health-conscious professional who skips breakfast, then has a lunch of grilled chicken breast and roasted broccoli. By the afternoon, they’re likely feeling tired, and they may still be hungry. Their blood sugar is low, so they grab whatever snacks are available in the office—whether it’s healthy or not. 

Starting the day with some carbs, protein, and healthy fats can disrupt this cycle, Schreckengaust says. Often, she’ll bring some carbs back into the routine if the client previously cut them out completely. 

“An effective diet cuts out carbs.” The most researched diets for healthy aging, like the Mediterranean, Dietary Approaches to Stop Hypertension (DASH), and MIND (Mediterranean-DASH Intervention for Neurodegenerative Delay) diets all feature carbohydrates. Carbs are also an important factor in gut health—they contribute to short-chain fatty acid production, which helps in maintaining a healthy gut microbiome. Fruits, vegetables, whole grains, beans, and legumes all also contribute to a diverse gut microbiome, which is linked to better digestive and metabolic health.

“After I work out, I need to fuel up on carbs—in 30 minutes or less.”

Someone working out regularly (i.e. three to six days per week) should be mindful of when they consume carbohydrates, Schreckengaust says.

But the idea that it’s necessary to eat 30 minutes after a workout is overly rigid, she says. 

She recommends some carbs before a workout—the amount will depend on the duration and intensity of the activity, along with the timing of your last meal. She also recommends eating some carbohydrates 1-2 hours after that workout, depending on the individual. (Some of her workout-fueling recommendations can be found here.) The real problem is not eating or eating very little in that 2-hour window, which often leads to snacking throughout the day in an attempt to “catch up” on the hunger that’s been accumulating since the workout.

The bottom line

In short, healthy carbohydrates are a valuable source of energy that should be matched to the demands one is placing on their body. Look to high-quality unrefined complex carbs for slow-digesting energy that also supplements your fiber and vitamin goals. 

Carb comparison based on activity level

The chart below shows how their carb requirements change when they are a high-volume athlete who trains 2-3 hours a day, every day, or a recreational athlete training 45-60 minutes a day, three times a week. 

Below is a daily breakdown of what their ideal carb intake might look like.