Nutrition 101. Phytonutrients (Phytochemicals)

Phytonutrients, also known as phytochemicals, are biologically active compounds of plants (apart from vitamins, minerals, proteins, carbohydrates, and fats). Plants produce these chemicals to protect themselves, but these substances are also known to benefit human health in a multitude of ways. Fruits, vegetables, grains, legumes, nuts and teas are rich sources of phytonutrients.

Overwhelming scientific evidence suggests that eating a variety of vegetables, fruits, and whole grains may lead to a lower risk for certain types of cancer (by preventing the formation of potential carcinogens, blocking the action of carcinogens on their target organs or tissue, or by suppressing cancer development), prevent and treat some chronic diseases, improve serum lipid (cholesterol) profiles, control levels of blood glucose, reduce the risk of cardiovascular and eye diseases, counter obesity, as some examples.

Phytonutrients work multiple ways. Some have predominantly antioxidant activity (which means protecting our cells against the damaging effects of excessive free radicals*), others  moderate cell functions (such as cell division or cell death), still others have hormone-like actions or provide anti-microbial effects.

There are many phytonutrient classifications, which are confusing because of the complexity and variety of these components. In any publication on phytochemicals, following the direct name association within this family of thousands of members is not easy. To give you a general appreciation of the phytonutrient family, here is an adapted version of The Linus Pauling Institute of Oregon State University classification:

  • Carotenoids: Alpha-Carotene, Beta-Carotene, Beta-Cryptoxanthin (these chemicals can be converted by the body to retinol, form of vitamin A), Lycopene, Lutein, and Zeaxanthin.These richly colored molecules provide the yellow, orange, and red colors of many plants. These nutrients aid in human eye health, benefit in treatment and prevention of some types of cancer, and reduce the risk of developing inflammatory disorders.
  • Chlorophyll and Chlorophyllin. Chlorophyll is the pigment that gives plants their green color. Its usefulness in cancer treatment and wound-healing is presently being investigated.
  • Curcuminoids, primarily Curcumin are found in turmeric and shown to have an anti-inflammatory effect.
  • Flavonoids and Lignans: A large family of polyphenolic (meaning containing multiples of phenol structural units) chemicals. Biological effects of flavonoids appear to be related to their ability to control cell division and cell death, which is critical in cancer management.
  • Fiber: is a very diverse group of substances and complex carbohydrates, which cannot be digested by human enzymes in the small intestine. Lignin, Cellulose, Beta-Glucans, Pectins, Gums, Resistant starch, for example. They help lower cholesterol and control blood sugar levels, promote digestive health to name a few health benefits.
  • Garlic and Organosulfur compounds: Crushing or chopping garlic releases an enzyme called alliinase that causes the formation of the major biologically active component of garlic. According to epidemiological studies, garlic is beneficial to health. Clinical effect of garlic in heart diseases, some cancers, and the common cold is under evaluation.
  • Indole-3-Carbinol and Isothiocyanates: Found in cruciferous vegetables, such as broccoli, cabbage, and kale, these are shown to have an anti – cancer effect.
  • Phytosterols: sterols and stanols: These are plant-derived complexes that are similar in structure and function to cholesterol and inhibit the intestinal absorption of cholesterol. They are naturally present in vegetable oils, nuts, legumes, whole grains, fruits and vegetables.
  • Resveratrol: found in grapes, red wine, purple grape juice, peanuts, and some berries. Current studies are assessing the role of resveratrol in coronary heart disease, diabetes, cancer and other diseases.
  • Soy Isoflavones: This is a class of phytoestrogens, plant-derived compounds with estrogenic activity. We are only just beginning to unravel the multifaceted effects of isoflavones on cancer.

Important considerations:

One must keep in mind that plant-based whole foods are complex mixtures of bioactive elements. Therefore, helpful information on the health effects of individual phytochemicals usually comes from information on the health effects of the whole foods that contain those phytochemicals. Attempts to study one component of the whole food separately from its complex source are complicated and the results are often confusing and can be misleading. This is one of the reasons why Dietary Reference Intakes (DRIs) for phytonutrients are not defined as they are for Vitamins, Minerals, Proteins, Fats and Carbohydrates.

Importantly, studies on individual phytochemical supplements did not show the same health benefits as whole food. There are many possible reasons for that:

  • The beneficial health effects of a diet high in vegetables and fruits or other phytonutrient – rich foods may be caused by differences in the chemical composition of nutrients in foods versus those in supplements.
  • Better health could be initiated or supported by other dietary factors present in the same foods or, indeed, the benefit could be prompted by additional lifestyle choices, geographical locations etc.
  • The effects of the large doses of compounds used in supplementation studies may not be equivalent to the effects of the smaller amounts of nutrients consumed in foods.
  • Combination of the several nutrients may be necessary to achieve beneficial effect.

It is not always clear which of the many compounds in vegetables and fruits have the greatest health value. Additionally, different vegetables and fruits are sources of different phytochemicals.

Bottom line: eating a variety of colorful produce every day will benefit your health in a multitude of ways.

Caution: Certain phytochemical supplements, especially when taken in large amounts, have side effects and, very importantly, can interact with some treatment drugs. If you decide to take phytochemicals in the form of a supplement when you are taking a treatment drug, be sure to talk to your doctor.


* Atom or group of atoms that has one or more unpaired electrons and therefore unstable. These radicals can be produced in the body by natural biological processes or introduced from outside (as in tobacco smoke, toxins, or pollutants), they can damage cells, proteins, DNA and lead to multiple diseases.