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Antioxidants and Oxidants: A Delicate Balance

Antioxidants and Oxidants: A Delicate Balance

  • Antioxidants prevent excess oxidation.
  • Oxidation is a normal metabolic process, but excess can be damaging to health.
  • Antioxidants can be found in foods that contain vitamin C and E, copper, zinc, manganese, selenium, and polyphenols.
  • Exercise induces adaptations to improve the body’s ability to deal with oxidation.

Antioxidants are touted as super foods, they will save any kind of health issue, you can never get too many antioxidants. Is this true? Well, they are pretty great, but to understand what an antioxidant is, we should first break down the word. The word “antioxidant” has two parts: anti- and -oxidant. Anti means against. However, the definition of oxidant is a bit more complex and requires a general understanding of the process of oxidation. Without getting too complicated, below is a brief summary of oxidation.

What is oxidation?

Oxidation is a biological process that occurs with normal metabolism, respiration (breathing), or in response to stress. As the name implies, oxidation uses oxygen to create molecules called free radicals. The most common free radicals are reactive oxygen species or ROS. All free radicals contain a molecule, like oxygen in the case of ROS, with an extra electron in its atomic structure. Atoms are the building blocks of all molecules, and electrons are critical components to the structure of atoms. Electrons always want to exist in pairs. Since free radicals have one extra electron, the free radical’s goal is to steal an electron from another molecule to build a pair. Then, the next molecule has an unpaired electron, and that molecule steals an electron from the next, and so on. This cycle proliferates indefinitely if unstopped. Having one extra electron makes the molecule highly reactive and unstable, but once the free radical steals an electron, it’s happy – i.e. it is no longer highly reactive or unstable.

Excess oxidation is referred to as oxidative stress and is associated with many diseases including atherosclerosis, cancer, and aging. Consequently, free radicals get a bad rap and have long been considered damaging with no beneficial biological activity. It is true that too many free radicals are harmful, however, they are critical signaling molecules. Free radicals oxidize (or steal electrons from) other molecules, like the lipids that make up our cell membranes, proteins used for signaling or the structure of our bodies, carbohydrates that are used for energy, and nucleic acids, like DNA. A regulated, normal amount of oxidation from free radicals is normal and can modify many biological processes, like signal transduction, enzyme activity, DNA repair, gene expression, and stress responses to name a few. So if a normal amount of free radicals is good, what is preventing an excess production? Well, you guessed it, antioxidants.

Antioxidants + Oxidants

Within our bodies, antioxidants and oxidants work in coordination to regulate oxidative processes. As described above, oxidants, or free radicals, are highly reactive molecules that steal electrons from other molecules. Antioxidants are a diverse group of compounds that mediate this process by donating an electron to a free radical. In turn, the antioxidant turns into a stable free radical. We just learned that having an unpaired electron is not good, so why do antioxidants do this? Well, when antioxidants donate an electron, resulting in an unpaired electron for themselves, they are WAY less reactive than other free radicals. This stops any proliferating oxidative processes that could be damaging. Therefore, it is desirable to have an abundance of antioxidants to mitigate potential damage caused from free radicals.

Fortunately, there are a few lifestyle factors that we can modify to affect the amount and efficiency of antioxidants in our bodies. These are mainly dietary intake and exercise.

Dietary Antioxidants

Certain foods, mostly plant foods, contain antioxidants, and these compounds can affect the antioxidants in our bodies directly and indirectly.

  • The compound in the food can quench free radicals, i.e. the compound can donate an electron to a free radical and stop any damage that is proliferating.
  • The compound can improve the activity of enzymes that quench free radicals or impair the activity of enzymes or processes that create free radicals.

The antioxidants we can consume through our diet are broken down into four main groups: 1) vitamins, 2) trace elements, and 3) polyphenols. These types of antioxidants can be found in a variety of foods, and their sources are listed below.

  1. Vitamins. Vitamins C and E are direct antioxidants. Both vitamin C and E are essential, meaning we must consume them in our diet, i.e. we cannot make them in our bodies.
  2. Trace Elements. Copper, zinc, manganese, and selenium are the primary trace elements involved in antioxidant activity and act indirectly.
  3. Polyphenols. Polyphenols are a broad group of compounds that seem to act directly and indirectly as antioxidants.

Dietary Sources of Antioxidants

Vitamin C Vitamin E
Citrus fruits (oranges, kiwis, grapefruits) Sunflower seeds
Red, green, and yellow peppers Almonds
Broccoli Hazelnuts
Strawberries Peanuts and peanut butter
Brussel sprouts Wheatgerm oil
Selenium Zinc Copper Manganese
Brazil nuts Oysters Beef liver Mussels
Yellowfin tuna Beef Oysters Pecans
Halibut Blue crab Dark Chocolate Hazelnuts
Sardines Pumpkin seeds Potatoes Brown rice
Ham Turkey Mushrooms Oysters
Phenolic Acids Flavonoids Stilbenes Lignans
Berries Berries Grapes
Wheat and rye bran
Tea Tea Dark Chocolate Flax seed
Coffee Onions Peanuts Oatmeal
Kiwis Apples Strawberries Brown rice
Cherries Cherries Tomatoes Lentils

Exercise and Oxidation

Although it seems counterintuitive, strenuous exercise, especially endurance activities like running or swimming, cause a significant burst of oxidative stress. This occurs primarily in muscle and is due to the increased metabolic demands induced by exercise, meaning more energy is needed to sustain the exercise at hand. Fortunately, exercise leads to metabolic adaptations allowing for an improved ability to handle oxidative stress in the future. In other words, exercise trains the body to more efficiently and effectively handle oxidative stress during and after exercise. The best way to reap the benefits of the exercise-induced physiological adaptations to oxidative stress is a long-term exercise routine.

Take Home Message

Oxidation is a normal biological process that, in excess, can lead to cellular damage. This damage is associated with a number of diseases, including cardiovascular disease and cancer. Antioxidants blunt oxidative stress and prevent prolific damage. The best sources of dietary antioxidants are found in fruits, vegetables, whole grains, nuts, and seeds. Exercise can also improve the body’s ability to handle oxidative stress, and strenuous endurance exercise is the most efficient way to accomplish this. Combining diet and exercise is the best way to ensure your body can handle oxidative stress.

Test Your Knowledge

True or False: Exercise causes oxidative stress.


Correct Answer: True

Explained: Exercise initially causes an acute burst of oxidative stress, which then leads to adaptations in the body that can better handle oxidative stress in the future.


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