In August, a TikTok trend where users snacked on Rice Krispies Treats before going to the gym made headlines across the web. The promise: Loading up on the processed food boosts athletic performance and results in #fitnessgains, a popular hashtag associated with this trend on the social media platform.
Fitness experts were quick to label the phenomenon — sometimes called carbohydrate (carb) timing or carb loading — as nothing new. And if you’ve ever prepared a heaping plate of pasta before a long cardio session like a race (an approach that long preceded the dawn of the internet), you get the idea.
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That said, the TikTok videos may have raised some interesting questions if you’re looking to optimize your fitness. Namely, can carb timing actually improve your workout? And if so, is there a right and wrong way to eat this macronutrient (the other two being protein and fat)?
The answer is complicated, many sports medicine performance specialists say, and depends on what type of workout you do, how long you go, and how hard you push yourself. Also, it depends on what else you ate and when, relative to the start of your workout, they say.
“If you’re meeting your daily carbohydrate requirements through your diet, then most workouts can be accomplished without the need for pre-workout carbs,” says Nick Tiller, PhD, a researcher at the Institute of Respiratory Medicine and Exercise Physiology at Harbor-UCLA Medical Center in California and author of The Skeptic’s Guide to Sports Science.
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 — and 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.
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What Are Carbs and Why Are They Needed for Exercise?
Carbohydrates — including sugars, starches, and fiber — are macronutrients that get broken down into glucose (blood sugar) in the digestive tract. Glucose then travels through the bloodstream and moves into cells, where it can be used for energy immediately or stored in our muscles and liver as glycogen, a form of sugar that can be used for fuel in the future.
When you exercise, carbs provide fuel for your workouts.
If you exercise without eating carbs first — and you tend not to have enough of these macronutrients in your diet to have a substantial reserve of glycogen in your muscles —your body breaks down protein in your muscles for fuel instead. Tapping these protein stores can make you fatigue more easily and more prone to dizziness and dehydration during intense workouts.
How Different Carbs Can Affect Your Workout
There are two types of carbs — simple and complex — and they can have different roles in fueling a workout.
Simple Carbs
Simple carbs are sugars that get broken down quickly in the body, rapidly sending glucose into the bloodstream, according to the Cleveland Clinic.
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. (For the record, Rice Krispies Treats fall into the latter, unhealthy category.)
This type of carb can cause a rapid spike in energy, followed by a feeling of fatigue.
While most registered dietitians will advise that you avoid simple carbs in your everyday diet, these foods may come in handy before a vigorous workout. Namely, If you snack before a workout, particularly in the morning, simple carbs are best to give you rapidly available fuel, according to the National Academy of Sports Medicine.
Decades of research have linked pre-workout simple carbs to benefits like better endurance. For example, a previous study found experienced cyclists doing exercise tests fatigued after 134 minutes without pre-workout carbs but lasted 157 minutes with a pre-workout drink of simple carbs. Another study also looked at cyclists and found they burned less glycogen in their muscles during workouts when they had simple carbs before exercise, and that they could exercise for longer before they fatigued compared with those participants who did not have simple carbs before exercise.
Drinks or smoothies with 300 to 400 calories are best within 60 minutes of your workout because they’re easily digested, the academy recommends. For more intense or longer workouts, consuming a 1,000 calorie meal two to four hours in advance may bolster your endurance.
When opting for simple carbs, the American Academy of Nutrition and Dietetics recommends choosing natural sources, such as fruit or milk with redeeming nutritional qualities versus added sources, like soda or candy. The American Heart Association recommends men eat no more than 9 teaspoons of added sugar per day, while women limit their intake to 6 teaspoons daily.
Complex Carbs
Complex carbs are fiber and starches, and they have a role in boosting exercise performance, too.
Compared with simple carbs, these take longer to break down into the body, creating more stable blood sugar levels. According to the Cleveland Clinic, examples of complex carbs are veggies, whole grains, legumes and beans, nuts and seeds, and fresh fruit with the skin on.
One of their benefits: Eating more whole grains can help boost stores of protein in our muscles and preserve muscle mass, according to a study published in September 2021 in Current Developments in Nutrition. This study compared the effect of a diet with lots of whole grains to a diet with lots of processed grains like white bread. It found 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.
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Do You Need Carbs for Moderate-Intensity Workouts?
Those benefits of simple and complex carbs sound impressive, but the truth is you may not need to change your carb intake at all before working out.
There’s an easy way to tell whether your workout is intense enough to require extra carbs at the start, says Chad Kersick, PhD, director of the exercise and performance nutrition laboratory at Lindenwood University in St. Charles, Missouri. He calls it the “talk test.”
If you can easily talk in complete sentences while working out, this is probably a low-intensity exercise, Dr. Kersick says. During a moderate-intensity workout, you will 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 of less than 60 minutes, you don’t need carbs beforehand, but if you like doing this it probably won’t hurt, says Kersick.
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What About Carbs for Vigorous-Intensity Exercise Sessions?
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.
“After about 90 to 120 minutes of exercise, it’s recommended to take on carbohydrates,” Tiller says. “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 work in this context because they give you a needed burst of energy to keep going at the point when your body has burned through all available glycogen stores, preventing you from tapping protein stores in your muscles. But sports drinks and gels shouldn’t be your go-to for shorter, less intense workouts when you’re not a pro athlete or running a marathon; in that case, they’ll just add extra calories that help you pack on pounds and cause unhealthy spikes in blood sugar.
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Most people need about 60 to 90 grams (g) of carbohydrates per hour, along with 500 to 1,000 mL of water, for optimal performance during longer, intense workouts, Tiller says.
The National Academy of Sports Medicine (NASM) recommends 14 to 22 ounces (oz) of fluid two hours before exercise, 6 to 12 oz of water or sports drink after every 15 to 20 minutes of exercise during a workout, and at least another 16 to 24 oz of water or sports drink after workouts.
As for carbs, NASM suggests that a 150-pound athlete needs about 68 g, or 4 to 5 servings of carbs, about one hour before exercise. Each of these servings has about 15 g of carbs, and can be combined to get the right amount for pre-workout fuel, according to NASM:
- One slice of whole grain bread
- One orange
- ½ cup cooked oatmeal
- One small apple
- ½ cup of lowfat yogurt
During workouts, 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, according to NASM.
For endurance races like marathons and triathlons, 60 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.
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What Is Carb Mouth Rinsing, and Can It Enhance Your Workout?
Early scientific evidence suggests you may not even need to ingest carbs to give your workout a boost — you may just need to swish them around in your mouth.
For example, in a randomized controlled trial published in May 2019 in Frontiers in Nutrition, seasoned cyclists who rinsed their mouths with a liquid solution made up of 6.4 percent carbs for five seconds then cycled at their preferred pace completed the distance, had a higher cycling output, and reported having a better workout compared with cyclists who consumed a similarly tasting placebo. That said, the study was small, with only 16 men, so more studies are needed.
A review of 11 additional studies on carb rinsing suggests the practice may help improve cycling power in some cases, though these studies were also small and the majority involved men. Researchers hypothesized that the reason carb rinsing may help is the macronutrient activates mouth and then the brain receptors associated with reward, signaling to your body that more energy is en route. These researchers noted that the effects of carb rinsing may be stronger when carb stores are low in the body, which may make receptors in the mouth more sensitive.
How to Build Workout-Enhancing Food With Carbs and Protein
Meals and snacks that combine carbohydrates with protein are best for sports performance, according to the Academy of Nutrition and Dietetics. While carbs supply the energy you’ll need to do your best, protein helps muscles rebuild and repair in response to a hard workout, whether eaten before or after your sweat session.
Some good choices for pre-workout snacks to have one to four hours before a workout:
- A peanut butter and banana or PBJ sandwich
- Greek yogurt with berries
- Oatmeal with low-fat milk and fruit
- Apple and peanut or almond butter
- Handful of nuts and raisins (two parts raisins, one part nuts)
After a workout, the Academy of Nutrition and Dietetics recommends these snacks, ideally within an hour of finishing sessions that are longer or more intense:
- Smoothie made with low-fat milk and fruit
- Low-fat chocolate milk
- Turkey on a whole-grain wrap with veggies
- Low-fat yogurt with berries
While these recommendations for pre- and post-workout snacks don’t specify an exact ratio of carbs to protein, the American Academy of Exercise recommends about 3 g of carbs for every 1 g of protein.
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