August 2016 Issue

Sports Nutrition: Antioxidant Supplements
and Athletic Performance

By Matt Ruscigno, MPH, RD
Today's Dietitian
Vol. 18 No. 8 P. 20

Athletes: There's probably no other group that focuses so intently on nutrition to benefit their lives and boost their performance—for better or for worse. For example, one day during a long bike ride, a professional cyclist friend of mine asked me about a particular supplement and its potential benefits. I explained that the science was unclear, more research was needed, and the supplement probably wasn't worth buying. "Though there is a chance it could help with no downside, right?" she asked. "If so, I'm going to take it, along with the dozen or so I already take."

At the professional level of competition, performance is everything, at nearly any cost. This is something recreational exercisers and competitors may not understand, but it's a belief system dietitians must familiarize themselves with if they're going to counsel athletes effectively. Many athletes take antioxidant supplements because they believe they can increase performance. But what does the research say about antioxidant supplementation and athletic performance? Let's take a closer look.

The Rationale
The broad concept behind antioxidant supplementation is relatively simple: Intense physical activity creates free radicals that damage cells and prolong recovery, and antioxidants reduce free radicals.1 So theoretically, consuming antioxidants like vitamin E and vitamin C should speed recovery. Athletes who eat plant-based diets, and therefore typically consume greater amounts of antioxidant compounds, claim that they can recover more quickly due to the antioxidants in plant foods. If they can recover more quickly, they can work out harder than or almost as hard as they did during their previous workout and improve their fitness level more dramatically.

However, when it comes to antioxidant supplementation and athletic performance, study findings are inconclusive, with some researchers arguing that supplementation can be problematic.2,3 During exercise, reactive oxygen species (ROS) are produced in skeletal muscle. These are the free radicals that damage cells after intense physical exertion. In a 2011 review on this topic in Sports Medicine, Peternelj and Coombes argue that while this may be true, the studies that show antioxidant supplementation negates this damage are limited. They postulate that the production of ROS and the damage to cells may be an important part of the training process for athletes, and supplementation may interfere. They recommend getting vitamins and antioxidants from a healthful diet.3

This brings to mind the much-touted 2013 meta-analysis and systematic review in the British Medical Journal that showed that antioxidant supplementation didn't reduce cardiovascular deaths.4 This meta-analysis focused on antioxidant supplements and not on antioxidant-rich foods, which are associated with a reduction in cardiovascular disease.5 The same could be true regarding the benefits of antioxidants for athletes: Evidence for supplementation isn't strong and may be conflicting, but eating whole plant foods as a source of antioxidants may make the difference. However, more evidence is needed, as this is a hot yet complicated topic for researchers.

Lowdown on Antioxidants
Oxidation is a common component of biochemical reactions, but an imbalance creates ROS, which lead to oxidative stress. Antioxidants, some of which are made endogenously (eg, glutathione and coenzyme Q10), manage and reduce this stress, theoretically. Anthocyanin, a phytochemical in the flavonoid group, for example, demonstrates antioxidant activity and is under consideration for reducing oxidative stress and improving performance.

One clinical trial found that athletes in the 100-mg anthocyanin supplement group had a statistically significant increase in maximal oxygen consumption.6 Food sources of anthocyanins include berries (particularly raspberries, blueberries, and blackberries), purple cabbage, plums, and cherries (especially tart cherries). In another clinical trial, researchers who worked with runners who consumed either tart cherry juice or a placebo for five days before and two days after a marathon found that the tart cherry group had reduced inflammation markers and showed a faster recovery in isometric strength.7

Beets, Blood Flow, and Chocolate
Beets are a unique source of the phytonutrient group called betalains. Betanin and vulgaxanthin, two examples of betalains, have anti-inflammatory and antioxidant properties. They're the source of the deep red color for which beets are known. Beets and, to a lesser extent, spinach and carrots, increase blood flow because of their nitrate content. Beets supply naturally occurring, nonsynthetic nitrates that are converted to nitric oxide, which increases vasodilation.

Blood vessels relax and widen during vasodilation. With wider blood vessels, more oxygen-rich blood flows through the body and reaches muscles sooner; this allows muscles to work at a high intensity for longer periods of time. Increased blood flow also helps to dissipate the heat created during physical activity.

Elite athletes have long tried to find ways to increase vasodilation, including through illegal substances. Consuming beets and beet juice currently is popular with athletes. And while there's been strong evidence that beets and beet juice improve athletic performance, more recent research has been less conclusive.8,9

Beets can be eaten raw, cooked, or juiced. Juicing beets leads to a greater concentration of the beneficial components, but requires an expensive at-home juicer. Clients can purchase packaged, store-bought juice, though this also can be pricey. Powdered beet supplements are available for athletes, but the jury is still out on their effectiveness. Diced beets can be added to salads, and roasted beets can make an excellent side dish.

According to a Harvard study, cacao, the bean from which chocolate is made, is associated with increased blood flow because of the positive effect flavanols have on the nitric oxide system.10 The theobromine in cacao also increases vasodilation. There's some evidence that dark chocolate has benefits on performance as well, possibly via this mechanism.11

Vitamin C
Vitamin C is found in high concentrations in whole fruits and vegetables. Papaya, bell peppers, broccoli, Brussels sprouts, strawberries, and pineapple all deliver more than 100% of the Recommended Dietary Allowance (RDA) per serving. These foods are nutrient dense and easy to incorporate into the diet as snacks or sides. Some athletes may take large supplemental doses of vitamin C, which results in poor absorption. It's mostly lost in the urine and isn't supported by evidence.

Vitamin E
Sunflower seeds, almonds, spinach, Swiss chard, avocado, and peanuts are excellent sources of the antioxidant vitamin E, providing more than 20% of the RDA. Turnips, beets, mustard greens, and asparagus are good sources and are very low in total calories. Nuts and seeds make great snacks and also can be added to main dishes and salads. They're calorically dense, so educating clients about appropriate serving size is important.

Berries are nutrient dense and antioxidant rich, as they contain both anthocyanins and flavonols. Smoothies made with frozen berries are common beverages among athletes because they make excellent and fast postworkout meals or snacks. Frozen berries also keep much longer than fresh berries. Berries are very low in calories and can be added to breakfast foods like pancakes, oatmeal, or yogurt. Tart cherries also are popular with athletes and can be eaten whole or juiced, and added to frozen desserts that are calorically dense for those with very high energy needs.

Leafy Greens
The antioxidant count and nutrient density of leafy greens is unmatched. The serving size of cooked greens is one-half cup. A hungry athlete easily can eat two cups in one sitting, therefore consuming four servings of antioxidants. Sautéed greens can be added to many meals like stir-fries, burritos, and wraps.

Arugula is especially rich in nitrates, containing more than beets. Called salad rocket in Europe, this spicy, leafy green can be eaten raw in salads or added to tacos.

Antioxidant-rich foods most often come packed with significant amounts of fiber. The benefits of fiber are clear and undisputed, but large amounts can be problematic for individuals who aren't used to eating several grams in one sitting. For example, too much fiber can negatively impact performance by moving stool through the gastrointestinal (GI) tract too fast during physical activity. Nevertheless, some athletes on plant-based diets consume upwards of 100 g per day without GI issues. If a client has a low-fiber diet, gradually increase high-fiber foods to give the GI tract time to adjust.

If GI distress is a concern for athletic clients, consider reducing the total number of grams of fiber consumed within the three to four days leading up to a big event.

Counseling Athletes
Athletes tend to be motivated and interested in nutrition, which can be both a plus and minus for dietitians who work with them. Often, advice must be accompanied with rationale related to performance. Athletes are influenced by a variety of factors including coaches, supplement manufacturers, employees at nutrition stores such as GNC, celebrity athletes with promotional contracts, and well-meaning family members. Dietitians are in a perfect position to explain the science behind antioxidant-rich foods and supplementation associated with athletic performance and other nutrition recommendations. Evidence on the benefits of antioxidant-rich foods for performance is still mixed, but we do know that these foods are beneficial for overall individual health, and this includes athletes. Plus, there's virtually no downside to adding whole plant foods to the diet, something my bike-racing friend can practice.

— Matt Ruscigno, MPH, RD, is the coauthor of No Meat Athlete: Run on Plants and Discover Your Fittest, Fastest, Happiest Self and a mere mortal who has raced ironmans, ultramarathons, and a 500-mile, nonstop bike race across Death Valley called the Furnace Creek 508. He has a private practice in Los Angeles.


1. Pingitore A, Lima GP, Mastorci F, Quinones A, Iervasi G, Vassalle C. Exercise and oxidative stress: potential effects of antioxidant dietary strategies in sports. Nutrition. 2015;31(7-8):916-922.

2. Slattery K, Bentley D, Coutts AJ. The role of oxidative, inflammatory and neuroendocrinological systems during exercise stress in athletes: implications of antioxidant supplementation on physiological adaptation during intensified physical training. Sports Med. 2015;45(4):453-471.

3. Peternelj TT, Coombes JS. Antioxidant supplementation during exercise training: beneficial or detrimental? Sports Med. 2011;41(12):1043-1069.

4. Myung SK, Ju W, Cho B, et al. Efficacy of vitamin and antioxidant supplements in prevention of cardiovascular disease: systematic review and meta-analysis of randomised controlled trials. BMJ. 2013;346:f10.

5. Ha V, de Souza RJ. "Fleshing out" the benefits of adopting a vegetarian diet. J Am Heart Assoc. 2015;4(10):e002654.

6. Yarahmadi M, Askari G, Kargarfard M, et al. The effect of anthocyanin supplementation on body composition, exercise performance and muscle damage indices in athletes. Int J Prev Med. 2014;5(12):1594-1600.

7. Howatson G, McHugh MP, Hill JA, et al. Influence of tart cherry juice on indices of recovery following marathon running. Scand J Med Sci Sports. 2009;20(6):843-852.

8. Lansley KE, Winyard PG, Bailey SJ, et al. Acute dietary nitrate supplementation improves cycling time trial performance. Med Sci Sports Exerc. 2011;43(6):1125-1131.

9. Rienks JN, Vanderwoude AA, Maas E, Blea ZM, Subudhi AW. Effect of beetroot juice on moderate-intensity exercise at a constant rating of perceived exertion. Int J Exerc Sci. 2015;8(3):277-286.

10. Fisher ND, Hurwitz S, Hollenberg NK. Habitual flavonoid intake and endothelial function in healthy humans. J Am Coll Nutr. 2012;31(4):275-279.

11. Patel RK, Brouner J, Spendiff O. Dark chocolate supplementation reduces the oxygen cost of moderate intensity cycling. J Int Soc Sports Nutr. 2015;12:47.


Rich Borscht With Cacao Accent

Beets and chocolate are great together, as they both have deep, earthy flavors and are antioxidant rich. Note that this recipe calls for 'cacao powder,' which isn't the same as cocoa powder. Cacao powder is much richer because it still contains the fatty acids from the bean, though it's harder to find (try health food stores, specialty shops, or online companies). Cocoa powder will work as a 1:1 substitute, but the texture will be different. The fat content of the recipe also will be reduced.

Serves 4

8 cups low-sodium vegetable, mushroom, or potato broth
2 cups diced potatoes
5 cups diced beets
1/2 cup chopped red onion
1/2 cup diced carrots
2 garlic cloves, minced
1 tsp dill, or to taste
1/2 tsp paprika
1/2 tsp caraway or cumin seed, crushed
1/3 cup raw cacao powder or to taste
2 to 3 T lemon juice
Chopped scallions, for garnish
Salt, to taste

1. Bring all ingredients, except the cacao powder, lemon juice, and scallions, to a boil in a large soup pot. Lower the heat to a simmer and cook for 20 minutes. Stir in the cacao powder and cook for another 20 minutes. Stir occasionally during this time.

2. Add the lemon juice and remove from the heat. Serve with the scallions and any other accompaniments you wish.

Variations: Mix up the ingredients for this soup by adding 1 cup chopped cabbage, 1 minced chile pepper, 1 cup sliced mushrooms, or 1 cup diced tempeh to the pot. Garnish with grated chocolate on each bowl before serving.

Nutrient Analysis per serving
Calories: 222; Total fat: 4 g; Sat fat: 2 g; Trans fat: 0 g; Sodium: 225 mg; Total carbohydrate: 42 g; Dietary fiber: 8 g; Sugars: 17 g; Protein: 6 g

— Reprinted with permission from Cacao: Superfoods for Life, by Matt Ruscigno, MPH, RD, with Joshua Ploeg (Fair Winds Press).