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Thank goodness for oxygen. Without it, you wouldn’t be able to run very far. The body consumes vast amounts of oxygen during sustained running—up to 15 times more than at rest. The body uses it to release energy from metabolic fuels, mainly glucose and fat, and power muscle activity.
But oxygen has a downside. A highly volatile molecule, it has a tendency to generate free radicals, a diverse array of chemicals that wreak havoc in the body. In the mind of the average person, free radicals are associated with oxidative stress, a type of damage to body tissues that over time may cause chronic disease and accelerated aging. Everyone who breathes is subject to oxidative stress. But because the body consumes so much more oxygen during running, it also produces many more free radicals, some of which contribute to muscle fatigue and to the muscle damage and inflammation that make it hard to run again the next day.
The natural enemies of free radicals are antioxidants, which neutralize free radicals and thereby limit their effects. There are two basic categories of antioxidants: endogenous and exogenous. Endogenous antioxidants are enzymes that your body manufactures to protect itself. Exogenous antioxidants come from the foods we eat (particularly fruits and vegetables). Thousands of scientific studies have demonstrated that a diet rich in antioxidants reduces oxidative stress and the risk of developing the diseases and conditions to which it contributes. For example, a 2014 study by researchers at Harvard Medical School reported that, in a population of 833,000 older men and women tracked over a multi-year period, each additional serving of fruit or vegetables in the diet reduced the chance of death occurring within that period by 5 percent.
Other research has shown that antioxidant-rich foods offer special benefits to runners and other endurance athletes. Brightly colored vegetables and fruits such as tart cherries typically have the highest concentrations of antioxidants. Tart cherries contain anthocyanins, a type of antioxidant that functions as a natural anti-inflammatory in the body. These compounds are especially concentrated in tart cherry juice, which is proven to help runners recover faster between runs. In one study, recreational runners were given either cherry juice or a placebo for five days before running a marathon. Afterward, The runners who’d gotten the cherry juice exhibited less muscle damage and lower levels of inflammation. They also recovered their muscle strength significantly quicker.
Tomatoes are scientifically proven also to supply exercise-specific benefits. As with tart cherries, the juice of the tomato contains a higher concentration of antioxidants (in this case beta-carotene and lycopene) than does the whole fruit. In 2012, researchers at Stockholm University found that tomato juice significantly reduced oxidative stress after exercise in a group of nonathletes. A year later, a team of Greek scientists asked nine out of 15 endurance athletes recruited as subjects to replace their regular sports drink with tomato juice during and after training for a period of two months. They reported that tomato juice significantly reduced biomarkers of muscle damage and inflammation.
Endurance athletes should take these findings as permission to choose a select few natural juices to consume as supplements to an “anything-goes” diet. To get the maximum health and fitness benefits from antioxidants, you need to maintain a balanced diet that includes a wide variety of antioxidant-containing whole foods. Nuts, milk, and even salmon contain antioxidants as well.
In fact, taking antioxidants in pill form may be counterproductive for runners. The reason is that the free radicals produced during exercise not only damage muscle tissue and hasten fatigue, but they also stimulate physiological adaptations that strengthen the body’s endogenous antioxidant defenses, making the muscles more resistant to the effects of free radicals in future workouts. Antioxidant supplements function as a kind of biochemical crutch that blunts these beneficial adaptations. In a recent review of the relevant science, Mitchell Gross of the University of Southern California concluded that, “for endurance athletes, antioxidant supplementation is not a case of ‘the more, the better’.”
Interestingly, new research suggests that antioxidants might be getting too much credit for the health benefits of fruits and particularly vegetables. Scientists have discovered that some of the credit goes to certain toxins that give these foods their bitter flavor. In living plants, these toxins protect against pests. But in the human body, they provoke a mild stress response that leads to health-increasing physiological adaptations—just as exercise itself does, in part by generating free radicals. It’s just another reason to eat your fruits and vegetables, and keep running!