Research shows that free radicals can wreak havoc on muscle tissue health, slowing recovery and impairing performance. With the right diet, athletes can take advantage of antioxidant power to ward off these effects.
By Lisa Dorfman
Lisa Dorfman, MS, RD, CSSD, LMHC, is Director of Sports Nutrition and Performance and an adjunct professor at the University of Miami. A former pro triathlete, she has completed more than 30 marathons, and can be reached through her Web site at: www.foodfitness.com.
Oxygen is the body's ATM for funding nearly every metabolic transaction. It helps the heart to beat, muscles to contract, and the digestive system to absorb nutrients from food. Oxygen is found in every molecule of water, which makes up nearly 60 percent of the body. During exercise, oxygen helps muscles utilize carbohydrates, protein, and fat to help athletes run faster, lift more, and keep going longer.
The body must metabolize a great deal of oxygen when an athlete works out, and while this essential process has numerous benefits, there are also side effects. One of them is the production of free radicals, a specific type of molecule that can damage tissue. But luckily, the body can be equipped to limit free radical damage with help from compounds called antioxidants.
You've no doubt heard of these substances, and probably seen advertisements for everything from fruit juices to dietary supplements touting antioxidant benefits. But do you know what antioxidants do, how they work, and how to make sure your athletes are taking advantage of their benefits? With sometimes confusing and conflicting research, that's not easy. But when helping athletes plan a diet that promotes optimal health and performance, antioxidants should definitely be part of the discussion.
During a workout, the body's overall oxygen level increases 10 to 20 fold, and as much as 100 to 200 fold in some individual muscle groups. As oxygen molecules are metabolized, they either partner up with other molecules in the body or remain unpaired. The unpaired loners are free radicals--free because they're not bonded to other molecules, radicals because their chemical structure makes them unstable and prone to react with other substances.
Free radicals can damage muscle protein, fats, and DNA within cells, producing both immediate and long-term effects. In the short term, free radical oxygen molecules can reduce muscle power and endurance during activity, contribute to fatigue, and initiate muscle soreness and even injury. In the long term, free radicals can weaken the immune system and play a role in the development of everything from heart disease and cancer to cataracts, arthritis, and several other chronic conditions.
In addition to the free radicals created as a byproduct of exercise, the body can also be bombarded by unhealthy oxidizing compounds from outside sources. Radiation, pollution, sunlight, food additives, alcohol, and caffeine can all contribute to free radical proliferation in the body. Taken together, these factors lead to oxidative stress--which for our purposes can be defined as physical damage and decreased performance caused by free radicals.
While exercise inevitably leads to some degree of free radical production, the extent of it is determined by numerous factors. Short exercise sessions produce fewer free radicals than long ones, and intense work performed in hot weather or at high altitude leads to greater free radical production. Studies suggest that training experience matters as well--over time, a well-conditioned body builds up its own defenses against free radical damage, particularly by "learning" how to protect muscle tissue.
LINE OF DEFENSE
Antioxidants are the primary chemical line of defense against the negative impact of free radicals. These compounds also help to repair cells already impacted by free radical damage.
The body produces some antioxidants on its own in the form of certain enzymes, such as superoxide dismutase, glutathione peroxidase, and catalase, which change the structure of free radicals and break them down. These enzymes essentially scavenge for and destroy free radicals throughout the body.
To support the endogenous antioxidants, we also consume them through diet. Exogenous antioxidants include vitamins A (carotenoids), C, and E, selenium, and various flavonoids. All these substances can help prevent free radical damage, and together with the body's natural antioxidants, they are the main source of protection for muscles and other tissue.
The strength of athletes' defenses against free radicals varies greatly, depending on age, genetic disposition, diet, lifestyle habits (such as smoking and alcohol use), physical activity level, and exposure to environmental toxins. Trained athletes generally have more finely tuned endogenous antioxidant systems working for them, while untrained or out-of-shape individuals, athletes early in their training season, those who are suddenly increasing training intensity or duration, and those training at high altitude or in extreme heat are most in need of antioxidant support through food or supplementation.
How does an athlete choose a diet rich in antioxidants? A relatively new method of measuring antioxidant potential in foods is called Oxygen Radical Absorbance Capacity (ORAC). This method, developed by scientists at The National Institute on Aging (a division of the National Institutes of Health) involves test tube analysis that determines the antioxidant levels of foods and other chemical substances.
In 2007, the U.S. Department of Agriculture published a list of ORAC values for 277 foods. (See "ORAC Values" for a link to the complete list, along with scores for select food items.) It revealed that some of the best natural sources of antioxidants are fruits, vegetables, legumes, and spices.
There's one important caveat: Knowing a food's ORAC score can be helpful in menu planning, but the exact relationship between ORAC values and antioxidant health benefits has not yet been established. Also, while foods with high ORAC scores are typically nutrient-dense and healthy overall, there are no magical properties associated with the ORAC score--just because food X scores 20 percent higher than food Y, that doesn't mean it is 20 percent better at protecting the body. In short, the jury is still out on exactly how much ORAC scores truly mean for physical health, but it's probably the best available starting point when seeking an antioxidant-rich diet.
ANTIOXIDANTS & PERFORMANCE
When researchers in the early 1980s first looked at the relationship between exercise and free radical production, they found a two to three fold increase in free radicals in the muscles and livers of rats during physical activity. Today, this relationship continues to be studied, using human subjects under specific training conditions, with a focus on trying to identify specific ways that free radical production hurts performance.
In general, research into free radicals and antioxidants has been plagued by inconsistency in the measurements used to gauge the role of dietary and supplemental antioxidants on oxidative stress. As a result, while we know that antioxidants offer some health benefits for athletes related to combating free radicals, it's difficult to be much more specific than that.
Studies have used widely varying exercise conditions, modalities, training intensities, genders, ages, and measures of oxidative stress through blood and urine. One newer test, called Raman spectroscopy, involves a laser light pointed at the fat pad of the palm to measure the amount of carotenoids in the body. So while progress continues, there are still many questions left to answer.
We do know that the importance of antioxidants for performance varies greatly from one sport to the next. For example, a 2006 study of endurance-training athletes working out at altitude for six weeks found that antioxidant levels in these athletes were below normal after the training sessions. This suggests that the antioxidants were doing their job neutralizing free radicals, and being used up in the process, helping to limit oxidative stress and likely boosting performance. But a 2009 study by the same researchers found that elite swimmers training for 13 days at altitude did not experience decreased antioxidant levels, suggesting that the antioxidants in their bodies (both endogenous and exogenous) didn't have to fight off free radicals and thus didn't play a significant role in performance.
Other studies have looked at specific antioxidant vitamins, such as vitamin C, and produced conflicting results on whether high doses can reduce post-workout muscle soreness and damage. Vitamin E, meanwhile, has been shown to enhance oxygen utilization at altitude, but does not seem to be as effective for that purpose at sea level.
What does all this mean? Essentially, it's not yet clear just how much oxidative stress affects athletic performance, but it likely contributes to muscle damage, decreased power, fatigue, and slow recovery. And while antioxidants' precise effects are still being debated and likely vary greatly from person to person and sport to sport, they can help limit oxidative stress and thus help protect the body. In summary, antioxidants can help many athletes, though the precise benefits are variable and not always well defined.
HOW MUCH IS ENOUGH?
Despite the many unknowns, Americans spend $2.3 billion a year on antioxidant supplements. Most of these products are marketed for their ability to protect muscle tissue, boost recovery, and improve athletic performance. If an athlete wants to maximize whatever benefits antioxidants may provide, there's an obvious question: What should they consume, and how much?
One thing research has told us quite clearly is that individuals' level of antioxidants varies greatly, based on diet, genetics, and other factors. It's likely that those who are chronically deficient in antioxidants (consistently consuming an amount below the recommended daily allowance) stand to experience the biggest gains, and might be able to improve performance and overall health by resolving the deficiency.
For example, one study found that vitamin C in supplement form improved performance among people who were shown in prior tests to be vitamin C deficient. However, well-nourished individuals (who were getting the recommended daily allowance of vitamin C through diet) did not experience an improvement due to supplementation.
Other studies have shown that high antioxidant consumption makes a difference only if it's consistent over a long period of time--using a supplement for just a week during a particularly intense training phase will probably not have a significant effect.
So just how much is enough? The National Academy of Sciences recommends that women should consume 75 milligrams of vitamin C daily, and men should consume 90 milligrams. For vitamin E, the standard recommendation is 15 milligrams per day for both genders, and for selenium, both men and women are advised to take 55 micrograms per day. Vitamin A's standard recommended allowance is 5,000 international units (IU) daily for men and 4,000 IU for women.
It shouldn't be difficult for most athletes to achieve these levels through food alone, and thus take full advantage of antioxidant benefits. Foods and beverages rich in vitamins A, C, and E, selenium, and polyphenol antioxidants can easily become a greater part of an athlete's daily diet.
In "On the Menu" below, I've provided two sample days' meal plans containing ample amounts of antioxidant-rich foods. But athletes don't have to follow a daily script to ensure they're getting enough antioxidants--a few simple guidelines can make all the difference.
For someone with a generally healthy diet, adding an ounce of trail mix with seeds and almonds and a peanut butter sandwich every day can provide the boost they need. For others, adding a leafy salad with a mix of vegetables and some green tea as a between-meal snack will do the trick. Fruits are another convenient choice--apples, oranges, cherries, berries, and cantaloupe are all packed with antioxidants.
If an athlete wants to boost antioxidant consumption but won't change their eating habits, beverages can be a great alternative. Coffee, green tea, and cocoa, along with fruit juices such as orange, apple, prune, grape, cherry, and berry are all rich in antioxidants. Spices like curcumin and parsley can also give the diet an extra antioxidant kick without really affecting food choices.
For athletes who want to use supplements, it's important to note that more is not always better when it comes to antioxidants, and in some cases it can actually be harmful. Doses far above the recommended daily allowance can shift intracellular antioxidant balance and pose serious health risks. For example, a few studies have shown that prolonged overconsumption of certain forms of vitamin A can increase some people's risk for lung cancer, and may also increase the rate of birth defects in pregnant women.
Athletes who do use antioxidant supplements should be advised of a value called the tolerable upper intake level (UL) for the substance(s) they're taking. This is the highest level of daily intake that's unlikely to pose a risk of adverse health effects.
The tolerable upper limits for some key antioxidants are:
• Vitamin A: 10,000 international units per day
• Vitamin C: 2,000 milligrams per day for adults; 1,800 milligrams per day for teens
• Vitamin E: 1,000 milligrams per day for adults; 800 milligrams for teens
• Selenium: 400 micrograms per day.
As with most aspects of sports nutrition, the lesson with antioxidants should be food first, and supplementation only if deemed necessary to resolve a deficiency. By eating a consistent diet containing a broad array of antioxidant-rich foods, athletes can rest assured they are equipping their bodies with compounds that can help protect their muscles, promote fast recovery, and optimize performance.
Sidebar: ON THE MENU
Here are two examples of antioxidant-rich daily meal plans:
• Whole-grain toast with
vegetable oil spread
• Yogurt with berries
• Glass of orange juice or lowfat chocolate milk
• Apple slices with dried fruit trail mix
• Iced green tea
• Green vegetable salad with carrots, tomatoes,
celery, and onion
• Vegetable oil dressing
• Grilled chicken breast
seasoned with curcumin
• Steamed broccoli
• Baked potato fries
• Berry juice blend
• Whole-grain crackers
• Baby carrots with dip
• Green salad
• Lean roast beef
• Steamed broccoli with
• Whole-grain roll
• Citrus fruit salad topped
with granola/trail mix
• Egg white omelet with spinach, tomatoes, and peppers
• Blueberry whole-grain waffle with berry fruit syrup
• Grape juice or lowfat
• Strawberry yogurt parfait topped with almond slivers
• Soy-based snack bar
• Spinach salad with shredded carrots, yellow peppers, and mushrooms
• Cinnamon-seasoned tuna wrap made with whole-grain tomato tortilla
• Orange juice
• Whole-grain pita chips
• Soy nut butter spread
• Mixed green salad
• Chicken stir fry with broccoli, carrots, and mushrooms
• Brown rice
• Honey almond soy crisps
• Sparkling water with lemon