June 2019 Issue

Carbohydrates — The Top-Tier Macronutrient for Sports Performance
By Jim White, RDN, ACSM EX-P
Today’s Dietitian
Vol. 21, No. 6, P. 32

Carbohydrates are the macronutrient everyone loves to hate.

Over the decades, carbs have waxed and waned in their favorability within the diet. In the 1960s, carbs were recognized as important fuel for athletes, while only 12 years later the Atkins diet was born and carbohydrates were demonized. In the 1980s, carb-loading was birthed into the sports world as athletes wanted to boost energy before events. By the 1990s, many processed carbs were seen as addictive and something to be limited, despite the USDA’s food pyramid recommendation of six to 11 servings of bread and grains per day. There have been many shifts in the language surrounding carbohydrates, and it’s no wonder why consumers are left confused.

Fad Diets
Currently, not much has changed in the hysteria and confusion surrounding carbohydrates. Especially in the fitness realm, protein is touted as the king of macronutrients. Low-carb diets have infiltrated sports nutrition, boasting the benefits of boosted energy and increased athletic performance. The ketogenic diet is the most prevalent of the low-carb diets today. Some athletes seek to burn more fat during activity to improve performance; however, most studies show no benefit to ketosis during activity. So, what’s the truth?

Fat compared with carbohydrates requires more oxygen to produce energy. This means low-carb athletes would have to work at a higher level to uptake more oxygen to produce comparable energy levels as those achieved with a higher-carbohydrate diet.1 Due to the misunderstanding of carbohydrates and limiting intake for weight loss in the physically inactive population, it can be forgotten that athletes have an unparalleled need for carbohydrates to preserve and enhance muscle glycogen storage during strenuous activity.2

Current research still points to carbohydrates as an essential energy source for high-intensity athletic performance. The American College of Sports Medicine recommends 6 to 10 g/kg/day of carbohydrates, and the National Strength and Conditioning Association recommends 5 to 10 g/kg/day. This means a 185-lb male athlete would need anywhere from 420 to 840 g carbohydrates per day.

From years of experience in practice, the following macronutrient goals work best: 60% carbohydrates, 20% protein, and 20% fat for cardiovascular athletes; 45% carbohydrates, 30% protein, and 25% fat for weight training athletes; and 55% carbohydrates, 25% protein, and 20% fat for both cardiovascular and weight training athletes.

Adequate carbohydrate intake can prevent muscle breakdown from glycogen depletion and prevent hypoglycemia, both of which have been independently proven to reduce athletic performance.2 During exercise, glycogen stores are depleted as muscle glycogen is converted to glucose and used for energy. Once this happens, the body needs alternative fuel sources and will turn to protein and fat in a process called gluconeogenesis. Having enough glycogen on board before exercise and refueling during workouts can help preserve skeletal muscle integrity during exercise. And as exercise intensity is increased, glycogen becomes progressively more important as a fuel source. Enhancing the muscle’s capacity to store glycogen can improve performance in sports where glycogen depletion would hinder athletic performance.3

During strenuous exercise, muscle tissue damage occurs and can continue after exercise. Due to the anabolic nature of insulin, it increases muscle amino acid uptake and protein synthesis while decreasing protein degradation. After exercise, raising the plasma insulin level within one hour is key for limiting muscle damage. In a study conducted by Roy and colleagues, carbohydrate supplementation post exercise raised plasma insulin levels and increased protein synthesis by 36% compared with controls. If athletes supplement only carbohydrates post workout, it’s best to do so every 30 minutes at a rate of 1.2 to 1.5 g/kg of body weight per hour. They can enhance muscle glycogen storage significantly by adding protein to a carbohydrate supplement. This reduces the amount of carbohydrate required to maximize glycogen storage. If athletes consume both a protein and carbohydrate supplement post workout, they should consume 0.8 g/kg carbohydrate plus 0.2 g/kg protein immediately following exercise as well as two hours afterward during a four-hour recovery period.3

Downside to Low-Carb Diets
Though growing in popularity, long-term low-carbohydrate diets are deemed potentially harmful to athletic performance. Research suggests that low-carb diets can lead to a decline in cognitive performance and mood, perceptions of fatigue, and lack of focus. Other data suggest a stronger risk of skeletal muscle damage during training or competing in individuals following a low-carb diet. Due to increased reliance on carbohydrates for energy during dehydration and decreased exercise economy from a low-carb diet, researchers are clear that low-carb diets make it difficult to sustain the intensity levels required for competitive and serious athletic performance.4 Aside from athletic performance, diets lacking adequate carbohydrate result in micronutrient deficiencies from reduced fruit and starchy vegetable intake and often lead to fatigue, constipation, and strong food cravings. There’s some evidence that the antioxidant quercetin (found in leafy vegetables, peppers, apples, grapes, green tea, red wine, and some fruit juices) has a trivial to small effect on VO2 max and endurance exercise performance; however, most studies are inconclusive on the general impact of antioxidants on exercise.5,6

Fueling and Refueling
To ensure proper muscle energy stores for sports performance, fueling and refueling before, after, and sometimes during a workout is imperative. Carbohydrate recommendations for preworkout fuel are 1 to 4 g/kg of body weight, depending on the intensity of the activity. Examples of balanced preworkout fuel are egg whites with breakfast potatoes and strawberries, Greek yogurt with berries and granola, or an apple with almond butter and a serving of whole grain crackers.

Activities lasting between 1 1/2 and two hours require carbohydrate refueling from 30 to 60 g/hour, while activities lasting between 2 1/2 and three hours require carbohydrate refueling up to 90 g/hour. Sports gels, sports drinks (6% to 8% dextrose solution), energy bars, fruit, and granola all serve as appropriate carbohydrate fuel sources for these types of activities.

Within 30 minutes post workout, 1 to 1.5 g/kg carbohydrate must be consumed to replenish glycogen stores lost during exercise. An example of a refuel meal would be steak, potatoes, and a side of asparagus or a protein shake with protein powder, fruit, milk, and oats.

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Carbohydrate Loading
Carbohydrate loading is a dietary practice used to enhance athletic endurance performance by supplying adequate glycogen to the muscles for stored energy. Muscular fatigue is closely tied to muscle glycogen depletion. Using the practice of carbohydrate loading to maximize these stores may enable an individual to perform at a higher submaximal intensity longer before reaching muscular exhaustion. Carb loading can improve athletic performance in sports such as marathons, triathlons, ultramarathons, ultraendurance events, Nordic skiing, and long-distance swimming or cycling.3

In addition, it has been suggested that mid- to late-game performance in intermittent high-intensity sports, such as soccer and football, might be improved by glycogen loading, specifically when starting levels are low.3 To achieve glycogen loading, athletes need to consume about 5 to 10 g carbs/kg of body weight throughout the day. Whole grains, fruits, and starchy vegetables are ways to meet this goal. A glycogen-loading meal may include baked chicken, a baked potato, one whole wheat dinner roll, roasted vegetables, a glass of milk, and a side of fruit salad.

Two studies assessed the impact of dietary changes on athletic performance. In the first study, hockey players were split into two groups, one given a high-carb meal and the other a normal mixed food meal. The high-carb group showed improvement in speed, distance, and time skating compared with the control group. The second study focused on mountain bikers. One group was provided a meal consisting of 1 g carbs/kg of body weight and the other 3 g/kg. The study found that the lower-carb group was faster for the first lap of the race, but by lap four all high-carbohydrate racers were ahead of the control group. These studies showed improved performance in endurance athletes who invest in carbohydrate loading before their event.7

To successfully reap the benefits of carbohydrate/glycogen loading, it should be combined with a six-day, gradually tapered exercise regimen. For example, the first three days of the taper should be around 50% of daily calories from carbs, while the last three days of the taper should be a high-carb diet with about 70% of calories from carbs. This practice can increase glycogen stores by about 50% to 70%. It’s important to note, however, that carb intake exceeding 10 g/kg body weight isn’t beneficial.

Counseling Clients
As dietitians, it’s important to explain the benefits of carbohydrates to athletic clients and the risks associated with limiting them. Many athletes confuse carbohydrates with being “fattening” and will limit them in their diets.1 This exclusion of fuel leads to fatigue, sluggishness, decreased athletic performance, and ineffective workouts. Educating patients on the difference between high-quality carbohydrates and refined carbohydrates can be helpful in dispelling any food fears or myths.

— Jim White, RDN, ACSM EX-P, is an award-winning fitness and nutrition spokesman and consultant for several national organizations, media outlets, and corporations. He’s the owner of Jim White Fitness & Nutrition Studios, MNT practices, and a workplace wellness corporation. White believes in the power of health and fitness and has founded a nonprofit organization, the LIFT Fitness Foundation, which focuses on creating a core of wellness to empower individuals in need.


1. Clark N. A low-carb diet for athletes? Separating fact from fiction. American Fitness website. https://magazine.nasm.org/american-fitness-magazine/issues/american-fitness-magazine-nov-dec-2015/a-low-carb-diet-for-athletes. Published 2015. Accessed April 2, 2019.

2. Hawley JA, Leckey JJ. Carbohydrate dependence during prolonged, intense endurance exercise. Sports Med. 2015;45(Suppl 1):5-12.

3. Ivy JL. Regulation of muscle glycogen repletion, muscle protein synthesis and repair following exercise. J Sports Sci Med. 2004;3(3):131-138.

4. Kanter M. High-quality carbohydrates and physical performance. Nutr Today. 2018;53(1):35-39.

5. Kressler J, Millard-Stafford M, Warren GL. Quercetin and endurance exercise capacity: a systematic review and meta-analysis. Med Sci Sports Exerc. 2011;43(12):2396-2404.

6. Smith-Ryan AE, Antonio J. Sports Nutrition & Performance Enhancing Supplements. Ronkonkoma, NY: Linus Learning; 2013.

7. Mueller A, Reek A, Schantzen J. Effects of carbohydrate loading on high performance athletics. https://cehsp.d.umn.edu/sites/cehsp.d.umn.edu/files/effectsofcarbohydrate
. Accessed April 2, 2019.