Friday, February 7, 2014

Nutritional value of phytochemicals and antioxidants

Plant –based foods contain thousands of natural chemicals called phytochemicals or phytonutrients. More than 1000 phytonutrients are found in plant foods. The word phyto in Greek means plants.  Phytochemicals generally protect the plants against bacteria, viruses, fungi and other pest organisms. These phytochemicals are found in plant – based foods such as fruits, vegetables, beans and grains.  The phytochemicals serve as antioxidants (cancer fighting chemicals), increase immunity, stimulate enzymes, and mimic hormone action and binds to cell walls. Nutritional scientists suggest that the foods containing phytochemicals, antioxidants and omega – 3- fatty acids reduce the risk of cancer development in human beings.

Mechanism of action of phytochemicals

1. Antioxidant effects – prevent free radical damage e.g., flavonoids phytochemicals
2. Effects on xenobiotic metabolism – detoxify and eliminate dietary carcinogens e.g., glucosinolates of cruciferous vegetables.
3. Hormonal effects (estrogenic/anti-estrogenic) – estrogenic activity of phytoestrogens e.g., isoflavones of soybeans.
4. Effects on signal transduction  (cell regulation) –regulate cascades of enzyme action.
5. Anti-inflammatory and immune stimulatory effects – immunostimulatory effects e.g., flavonoids, phytoestrogens.

General category of phytochemicals

They include carotenoids, ellagic acid, flavonoids, resveratrol, glucosinolates and phytoestrogens.

More than 600 carotenoids present in fruits and vegetables give yellow, orange and red colours. Carotenoids include alpha –carotene, beta-carotene and  beta – cryptoxanthin.  Human body can convert all of these phytochemicals into vitamin A. Carotenoids act as antioxidants, help to improve immunity. Yellow and orange foods like pumpkin and carrots are good source of alpha and beta –carotene whereas sweet red peppers contain beta-cryptoxanthin. Lycophene gives red or pink colour to tomatoes, water melon and pink grapes. Lutein and Zeaxanthin  are present in greens such as spinach, kale, and collards. These chemical prevent cataract, age-related macular degeneration and eye problems.
Ellagic acid is found in straw berries, rasp berries and pomegranates. They help to protect from cancers.
Flavonoids are pigments that are responsible yellow, orange and red colour in foods. They include catechins (green tea), hesperidin (citrus fruits) and flavonols (apples, berries, grapes and onions. They all help to prevent cancers.
Resveratrol  is found in grapes and red wine. It acts both as antioxidants and anti-inflammatory agents.
Phytosterols are found in almonds, cashews, pea nuts, soyabeans, maize, and whole wheat.
Tocopherol is vitamin E present in dark green leafy vegetables, legumes and nuts.


They are substances that inhibit the oxidation process and act as protective agents of human body. They protect the body from dangerous free radicals, which normally form during chemical processes. Free radicals are incomplete, highly unstable, reactive compounds or molecules.Free radicals are continuously produced in our cells. Free radicals attack healthy cells and damage our genetic material DNA and allowing cancers to develop. Antioxidants protect the body from such free radicals e.g., vitamin C, beta carotene and vitamin E. Polyphenols scavenge carcinogens and mutagens. Carotenoids and ascorbates quench free radicals. Sulfur- containing compounds can stimulate DNA repair.Certain phytochemicals can alter hormone metabolism.

Health benefits of antioxidants

  1. Antioxidants prevent or neutralize or delay the oxidation reactions caused by free radicals.
  2. Antioxidants play a beneficial role in the prevention of disease e.g, heart disease, stroke. They slow the aging process.
  3. Antioxidants prevent free radical damage to the delicate lining of blood vessels, brain and nervous system.
  4. Antioxidants prevent or interfere with the development of cancer. They protect human body cells from the ravages of inflammation. Inflammation is known to be associated with increased levels of lipid peroxides and free radicals.
  5. Antioxidants are critical enzyme helpers.

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