Carbohydrates are the body’s main source of energy during exercise. With that in mind, a concept called carb timing is crucial to understand.
Carb timing refers to strategically eating carbohydrates before, during, or after workouts to support energy levels, performance, and recovery. Popular among athletes and fitness enthusiasts, carb timing promises better workouts — but does the concept actually deliver?
The short answer? It’s complicated. The efficacy of carb timing depends on the type, duration, and difficulty of a workout. Also, what else you ate and when, relative to the start of your workout, may also matter.
Carb Timing, Explained
Carbohydrates — including sugars and starches — are macronutrients your body breaks down into glucose (blood sugar) in the digestive tract. Glucose then travels through the bloodstream and moves into cells, where your body can use it immediately for energy or store it as glycogen, a form of sugar to use for future fuel. When you exercise, carbs provide fuel for your workouts.
If you don’t have enough of these macronutrients in your diet to build a substantial reserve of glycogen in your muscles, you may have a low store of carbohydrates. Low carbohydrate stores can lead to faster fatigue and make you more prone to dizziness and dehydration during particularly intense workouts.
This is how carb timing — the strategic consumption of carbs to elevate fitness performance — can come into play.
As to whether carb timing is necessary, that depends on a few factors. “If you’re meeting your daily carbohydrate requirements through your diet, then most workouts can be accomplished without the need for preworkout carbs,” says Nick Tiller, PhD, a researcher at the Lundquist Institute at Harbor-UCLA Medical Center in California and author of The Skeptic’s Guide to Sports Science. Here’s where workout duration and intensity comes into play.
How Workout Intensity Influences the Need of Carb Timing
Carb loading before a workout may sometimes make sense when you’re planning to exercise for more than 90 minutes or if you’re doing high-intensity workouts, like interval training, Dr. Tiller says.
These are circumstances when it’s possible for the body to burn through its stored carbohydrates. High-carbohydrate drinks or gels might help prevent fatigue, Tiller says. With shorter, less vigorous workouts, however, the body will probably have enough stored carbohydrates to perform just fine without loading up on carbs beforehand.
Low- and Moderate-Intensity Workouts
Want a quick way to tell whether your workout is intense enough to require extra carbs at the start? According to Chad Kersick, PhD, associate professor of exercise science at Lindenwood University in St. Charles, Missouri, the “talk test” can help.
If you can easily speak in complete sentences while working out, this is probably a low-intensity exercise, Dr. Kersick says. During a moderate-intensity workout, you’ll only be able to string together a few words before you need a deep breath. And if talking at all is a challenge, your workout is intense.
For a low- or moderate-intensity workout fewer than 60 minutes, you likely don’t need to eat carbs beforehand, but if you like doing so, it probably won’t hurt, he adds.
High-Intensity Workouts
When your workouts get more intense and last longer, you’ll want to think about refueling as you go, Tiller says. This is where simple carbs can be helpful.
If you’re doing a workout that lasts longer than 60 minutes, experts recommend you take in small amounts of carbs (around 10 to 15 grams) starting 15 to 20 minutes into your session. From there, continue to supplement with additional carbs every 20 minutes of your workout.
“This is usually in the form of sports drinks or gels because they’re simple sugars, absorbed quickly by the gut and delivered to the muscle, but any good source of carbohydrate that won’t cause stomach upset will be fine,” Tiller says.
Sports drinks and gels may often get special billing in the fitness world because they can provide the burst of energy when your body has burned through all available glycogen stores, preventing you from tapping protein stores in your muscles.
But sports drinks and gels aren’t necessary for shorter, less intense workouts. In these cases, plain water is typically sufficient for helping you complete your workout and improve your fitness.
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How Different Carbs Can Affect Your Workout
Let’s say you’re doing high-intensity workouts that would benefit from carb timing. Even in this case, it’s important to know that not all carbs are equivalent, and the differences can be impactful.
There are two types of carbs — simple and complex — and they have different roles in fueling a workout.
Simple Carbs
Simple carbs are sugars that break down quickly in the body, rapidly sending glucose into the bloodstream.
Notably, sugar comes in two types: natural and added. Sources of natural sugar include fresh fruit and milk, while added sugar often resides in processed foods and drinks, like packaged sweets, soda, and fruit juice.
This type of carb can cause a swift energy spike, followed by a feeling of fatigue.
While typically less nourishing than complex carbs (more on this below), simple carbs may come in handy before and during a vigorous or long workout because your bloodstream absorbs them quickly, allowing you to access the energy you need immediately. For instance, if you snack before a workout, particularly in the morning, simple carbs are great for providing available fuel.
When opting for simple carbs, prioritize natural sources, such as fruit or milk, with redeeming nutritional qualities versus added sources, like soda or candy. That said, though sports drinks and gels are simple carbs that contain added sugars, consuming these products during exercise is acceptable because you burn them off right away.
The American Heart Association (AHA) recommends men eat no more than 9 teaspoons (tsp) of added sugar per day, while women limit their intake to 6 tsp daily.
Complex Carbs
Complex carbs are fiber and starches. They also have a role in boosting exercise performance.
Compared with simple carbs, complex carbs take longer to break down into the body, creating more stable blood sugar levels. Examples of complex carbs are veggies, whole grains, legumes and beans, nuts and seeds, and fresh fruit with the skin on.
Among the benefits of eating complex carbs is that they can help retain stores of protein in our muscles and preserve muscle mass, which is of particular note for the purpose of carb timing.
In one study, researchers compared the effect of a diet with lots of whole grains to a diet with lots of processed grains, like white bread. Results concluded that people who ate whole grains performed better on walking-speed tests, had higher stores of protein in their muscles, and had better overall muscle function than people who did not eat these healthy foods.
How to Effectively Practice Carb Timing
Most people need about 30 to 60 grams (g) of carbohydrates per hour and up to 90 g for longer or very intense exercise. Additionally, aim to minimize your fluid loss to less than 2 to 3 percent of your body weight.
As for carbs, the National Academy of Sports Medicine (NASM) suggests that a 150-pound athlete needs about 68 g, or four to five servings, of carbs about one hour before exercise. Each of these servings contains about 15 g of carbs and can be combined to get the right amount for preworkout fuel, according to NASM:
During workouts, the NASM recommends 30 to 60 g of carbs per hour when workouts are longer than an hour and more intense. Afterward, a 150-pound athlete may need another 68 to 102 g of carbs to aid recovery.
For endurance races like marathons and triathlons, 30 to 90 g of carbs an hour will still do the trick, but people shouldn’t wait so long to refuel, Tiller advises. Starting to replenish carbs after only 30 to 60 minutes, before muscles fatigue too much, will aid performance.
What to Know About Carb Mouth Rinsing
As it turns out, you might be able to reap the energy-fueling benefit of carb timing without actually consuming the nutrient. Carb mouth rinsing involves rinsing with a carbohydrate solution. According to research, it may enhance aspects of workout performance through a central (brain-mediated) mechanism rather than a metabolic one.
One systematic review and meta-analysis published in 2025 on carbohydrate mouth rinsing found it improved exercise performance in fed conditions by stimulating oral receptors linked to brain areas involved in motor control and motivation — even without swallowing the carbs. The analysis showed a small but statistically significant performance benefit on exercise outcomes when compared with placebo rinses.
The Takeaway
Carb timing focuses on when you eat carbohydrates to support energy, performance, and recovery.
It may benefit endurance athletes and people doing long or intense workouts the most.
For shorter or lower-intensity exercise, carb timing is less likely to make a noticeable difference.
Overall carb quality and total intake matter more than precise timing for most people.
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
Henselmans M et al. The Effect of Carbohydrate Intake on Strength and Resistance Training Performance: A Systematic Review. Nutrients. February 18, 2022.
Mey JT et al. A Whole-Grain Diet Increases Whole-Body Protein Balance Compared with a Macronutrient-Matched Refined-Grain Diet. Current Developments in Nutrition. September 25, 2021.
Podlogar T et al. New Horizons in Carbohydrate Research and Application for Endurance Athletes. Sports Medicine. September 29, 2022.
Tara Collingwood, RDN, is a board-certified specialist in sports dietetics, an American College of Sports Medicine–certified personal trainer, and a media spokesperson. As a sports dietitian, she has worked with the U.S. Tennis Association, the Orlando Magic, World Wrestling Entertainment, runDisney, the University of Central Florida, and numerous professional and amateur athletes. Collingwood is the author of Pregnancy Cooking and Nutrition for Dummies and a coauthor of the Flat Belly Cookbook for Dummies.
She appears regularly on national and local TV, and speaks around the world to business teams on how to manage energy physically, emotionally, mentally, and spiritually. She previously served as a national spokesperson for the Academy of Nutrition and Dietetics.
Collingwood double-majored in dietetics as well as nutrition, fitness, and health at Purdue University and earned a master's degree in health promotion from Purdue University.
Lisa Rapaport is a journalist with more than 20 years of experience on the health beat as a writer and editor. She holds a master’s degree from the UC Berkeley Graduate School of Journalism and spent a year as a Knight-Wallace journalism fellow at the University of Michigan. Her work has appeared in dozens of local and national media outlets, including Reuters, Bloomberg, WNYC, The Washington Post,Los Angeles Times, Scientific American, San Jose Mercury News, Oakland Tribune, Huffington Post, Yahoo! News, The Sacramento Bee, and The Buffalo News.
