13 Antioxidants and Phytochemicals


  • Antioxidants
  • How antioxidants help support health and prevent disease
  • Phytochemicals in foods
  • Free radicals


The market is flooded with advertisements for “super antioxidant” supplements teeming with molecules that block free radical production, stimulate the immune system, prevent cancer, and reduce aging signs. Based on the antioxidant-supplement industry’s success, the general public appears to believe these health claims. However, these claims are not backed by scientific evidence; rather, some evidence suggests that supplements can actually cause harm. While scientists have found evidence supporting the consumption of antioxidant-rich foods as a method of reducing the risk of chronic disease, there is no “miracle cure”; no pill or supplement alone can provide the same benefits as a healthy diet. Remember, it is the combination of antioxidants and other nutrients in healthy foods that is beneficial. This section will review how particular antioxidants function in the body, learn how they work together to protect the body against free radicals, and explore the best nutrient-rich dietary sources of antioxidants. One dietary source of antioxidants is vitamins, some of which also function as antioxidants.


Antioxidants & Free Radicals

Watch this video to gain a better understanding of how free radicals harm the body.


 Antioxidants and Their Function in the Body

Vitamin A Protects cellular membranes, prevents glutathione depletion, maintains free radical detoxifying enzyme systems, reduces inflammation
Vitamin E Protects cellular membranes, prevents glutathione depletion.
Vitamin C Protects DNA, RNA, proteins, and lipids, aids in regenerating vitamin E
Carotenoids Free radical scavengers
Lipoic acid Free radical scavenger aids in regeneration of vitamins C and E
Phenolic acids



Free radical scavengers protect cellular membranes.

Cofactor of free radical detoxifying enzymes, maintains glutathione levels, aids in regeneration of vitamins C & E.

Protects cellular membranes and decreases oxidative damage

Introduction to Phytochemicals

Watch this short video overview of phytochemicals.



Phytochemicals are chemicals in plants that may provide some health benefits. They are not considered nutrients as they are not required to sustain life; however, consuming foods with phytochemicals on a regular basis has been linked to reducing risk for cardiovascular disease, diabetes, and cancer, as well as age-related physical and mental decline. Carotenoids are one type of phytochemical. Phytochemicals also include indoles, lignans, phytoestrogens, stanols, saponins, terpenes, flavonoids, carotenoids, anthocyanidins, phenolic acids, and many more. Phytochemicals are found in fruits, vegetables, grains, seeds, nuts, and legumes; and they are what give plants their color.

  • Carotenoids are found in foods that are red, orange, and deep green.
  • Flavonoids are found in berries, black and green tea, purple grapes, and chocolate.
  • Phenolic acids are found in coffee beans and fruits.
  • Phytoestrogens are found in soy products.
  • Indoles are found in garlic, leeks, and onions.

Phytochemicals are present in small amounts in the food supply, and although thousands have been and are currently being scientifically studied, their health benefits remain largely unknown. Also largely unknown is their potential for toxicity, which could be substantial if taken in large amounts in the form of supplements. Moreover, phytochemicals often act in conjunction with each other and with micronutrients. Thus, supplementing with only a few may impair the functions of other phytochemicals or micronutrients. The antioxidant vitamins are the mixture and variety of phytochemicals in foods linked to health benefits. Many phytochemicals act as antioxidants, but they have several other functions, such as mimicking hormones, altering cholesterol absorption, inhibiting inflammatory responses, and blocking certain enzymes’ actions.


Learning Objectives

  • Identify vitamins that serve as antioxidants. (MCCCD Competency 1)
  • Explain the function of antioxidants in disease prevention. (MCCCD Competency 6)
  • Identify which foods contain phytochemicals. (MCCCD Competency 6)
  • Explain how free radicals attack your body and how to prevent damage. (MCCCD Competency 1)



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Nutrition Essentials Copyright © 2020 by Stephanie Green and Kelli Shallal is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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