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Antioxidants are substances that can prevent or slow damage to cells caused by free radicals, unstable molecules that the body produces as a reaction to environmental and other pressures.
They are sometimes called “free-radical scavengers.”
The sources of antioxidants can be natural or artificial. Certain plant-based foods are thought to be rich in antioxidants. Plant-based antioxidants are a kind of phytonutrient, or plant-based nutrient.
The body also produces some antioxidants, known as endogenous antioxidants. Antioxidants that come from outside the body are called exogenous.
Free radicals are waste substances produced by cells as the body processes food and reacts to the environment. If the body cannot process and remove free radicals efficiently, oxidative stress can result. This can harm cells and body function. Free radicals are also known as reactive oxygen species (ROS).
Factors that increase the production of free radicals in the body can be internal, such as inflammation, or external, for example, pollution, UV exposure, and cigarette smoke.
Antioxidants are said to help neutralize free radicals in our bodies, and this is thought to boost overall health.
Antioxidants can protect against the cell damage that free radicals cause, known as oxidative stress.
Activities and processes that can lead to oxidative stress include:
- mitochondrial activity
- excessive exercise
- tissue trauma, due to inflammation and injury
- ischemia and reperfusion damage
- consumption of certain foods, especially refined and processed foods, trans fats, artificial sweeteners, and certain dyes and additives
- environmental pollution
- exposure to chemicals, such as pesticides and drugs, including chemotherapy
- industrial solvents
Such activities and exposures can result in cell damage.
This, in turn, may lead to:
- an excessive release of free iron or copper ions
- an activation of phagocytes, a type of white blood cell with a role in fighting infection
- an increase in enzymes that generate free radicals
- a disruption of electron transport chains
All these can result in oxidative stress.
The damage caused by oxidative stress has been linked to cancer, atherosclerosis, and vision loss. It is thought that the free radicals cause changes in the cells that lead to these and possibly other conditions.
An intake of antioxidants is believed to reduce these risks.
According to one study: “Antioxidants act as radical scavenger, hydrogen donor, electron donor, peroxide decomposer, singlet oxygen quencher, enzyme inhibitor, synergist, and metal-chelating agents.”
Overall, however, there is a lack of evidence that a higher intake of specific antioxidants can reduce the risk of disease. In most cases, results have tended to show no benefit, or a detrimental effect, or they have been conflicting.
There are thought to be hundreds and possibly thousands of substances that can act as antioxidants. Each has its own role and can interact with others to help the body work effectively.
“Antioxidant” is not really the name of a substance, but rather it describes what a range of substances can do.
Examples of antioxidants that come from outside the body include:
Flavonoids, flavones, catechins, polyphenols, and phytoestrogens are all types of antioxidants and phytonutrients, and they are all found in plant-based foods.
Each antioxidant serves a different function and is not interchangeable with another. This is why it is important to have a varied diet.
The best sources of antioxidants are plant-based foods, especially fruits and vegetables.
Foods that are particularly high in antioxidants are often referred to as a “superfood” or “functional food.”
To obtain some specific antioxidants, try to include the following in your diet:
Vitamin A: Dairy produce, eggs, and liver
Vitamin C: Most fruits and vegetables, especially berries, oranges, and bell peppers
Vitamin E: Nuts and seeds, sunflower and other vegetable oils, and green, leafy vegetables
Beta-carotene: Brightly colored fruits and vegetables, such as carrots, peas, spinach, and mangoes
Lycopene: Pink and red fruits and vegetables, including tomatoes and watermelon
Lutein: Green, leafy vegetables, corn, papaya, and oranges
Selenium: Rice, corn, wheat, and other whole grains, as well as nuts, eggs, cheese, and legumes
Other foods that are believed to be good sources of antioxidants include:
- legumes such as black beans or kidney beans
- green and black teas
- red grapes
- dark chocolate
- goji berries
Goji berries and many other food products that contain antioxidants are available to purchase online.
Foods with rich, vibrant colors often contain the most antioxidants.
The following foods are good sources of antioxidants. Click on each one to find out more about their health benefits and nutritional information:
Effect of cooking
Cooking particular foods can either increase or decrease antioxidant levels.
Lycopene is the antioxidant that gives tomatoes their rich red color. When tomatoes are heat-treated, the lycopene becomes more bio-available (easier for our bodies to process and use).
However, studies have shown that cauliflower, peas, and zucchini lose much of their antioxidant activity in the cooking process. Keep in mind that the important thing is eating a variety of antioxidant-rich foods, cooked and raw.
The following tips could help increase your antioxidant intake:
- Include a fruit or a vegetable every time you eat, meals and snacks included.
- Have a cup of green or matcha tea every day.
- Look at the colors on your plate. If your food is mostly brown or beige, the antioxidant levels are likely to be low. Add in foods with rich colors, such as kale, beets, and berries.
- Use turmeric, cumin, oregano, ginger, clove, and cinnamon to spice up the flavor and antioxidant content of your meals.
- Snack on nuts, seeds, especially Brazil nuts, sunflower seeds, and dried fruit, but choose those with no added sugar or salt.
Or, try these healthy and delicious recipes developed by registered dietitians:
- Cherry-almond smoothie
- Spicy cinnamon-ginger roasted carrots
- Roast beet and red quinoa salad with orange-beet balsamic vinaigrette
- Carrot cake power smoothie
- Chickpea, kale and cashew superfood soup
- Spicy Thai lettuce wraps
- Cure-all juice.
There is no set recommended daily allowance (RDA) for antioxidants, but a high intake of fresh plant-based produce is considered healthful.
It is worth remembering that, while studies link the consumption of fruits and vegetables with better overall health, it is not clear whether how far this is due to the activity of antioxidants. In addition, caution is needed regarding supplements.
The National Institutes of Health (NIH) warn that high doses of antioxidant supplements can be harmful.
A high intake of beta-carotene, for example, has been linked to an increased risk of lung cancer in smokers. A high dose of vitamin E has been found to increase the risk of prostate cancer, and the use of some antioxidant supplements has been linked to a greater risk of tumor growth.
Antioxidant supplements may also interact with some medications. It is important to speak with a health provider before using any of these products.
Overall, research has not proven that taking any particular antioxidant as a supplement or through a food can protect against a disease.
There may be some benefit for people at risk of age-related macular degeneration, but it is essential to seek advice from a doctor about whether to use supplements, and which ones to use.
Free radicals have been linked to a range of diseases, including heart disease, cancer, and vision loss, but this does not mean that an increased intake of antioxidants will prevent these diseases. Antioxidants from artificial sources may increase the risk of some health problems.
As a result, it is important to seek out natural sources of antioxidants, in the form of a healthful diet.
Consuming fruits and vegetables has been linked to a lower rate of chronic diseases, and antioxidants may play a role. However, it is unlikely that consuming added antioxidants, especially in processed foods, will provide significant benefits.
In addition, anyone considering taking antioxidant supplements should speak to a health provider first.