Phytochemicals: Cancer and Chronic Disease Fighters, Immune Boosters, Heart Helpers


Think about what you’ve eaten over the past several days. Do you eat a wide variety of foods or do you easily get into a routine of eating the same foods every day? Is your diet colorful or is it mostly beige?

Variety and Color

If your diet lacks a variety of colorful vegetables and fruit you may be missing important vitamins, minerals, and fiber. Many Americans consume diets that are deficient in nutrients that support good health. Before you reach for a multivitamin, know that the best way to get the nutrients you need is to consume a varied diet of whole plant foods. In fact, consuming at least two and a half cups of vegetables and fruit per day is associated with a reduced risk of cardiovascular and other chronic diseases, and protection against certain types of cancer. (1)

What are Phytochemicals?

There is another powerful reason to consume a wide variety of plant foods. Besides delivering a rich source of vitamins, minerals, and fiber, whole plant foods contain an important class of compounds called phytochemicals or phytonutrients. (2) Phytochemicals are naturally occurring plant chemicals (phytois Greek for plant) that give plant foods their color, flavor and odor. (2) Think purple grapes, dark leafy greens and bright orange sweet potatoes, the bitter taste of endive, the pungent odor of an onion, and the unique nutty flavor of almonds or pecans. 

Plants can’t fight their enemies or hide from them, so they develop chemicals compounds to defend against oxidative and environmental stressors and pests like UV radiation, insects, microbes, animals and parasites. (2) Tens of thousands of phytochemicals have been identified in vegetables and fruits, as well as nuts, seeds, beans, legumes, herbs and spices. (3,4) When we consume phytochemical-containing foods, their plant protective qualities provide protection for our human cells. (3,4)

A wide range of phytochemicals have been confirmed to have health-promoting functions in preventing cardiovascular disease, cancers, obesity and diabetes, as well as lowering blood cholesterol levels, and reducing inflammation. (3) Findings from laboratory research have found that phytochemicals can stimulate the immune system, prevent DNA damage and facilitate DNA repair, block substances that we eat, drink or breathe from becoming carcinogens, and slow the growth of cancer cells.5Many are powerful antioxidants and provide protection against free radical damage. (3,4) Others have been found to regulate physiological functions that prevent disease through their ability to alter cell signaling pathways and gene expression. (3)

Best Sources and Health Benefits

You are probably familiar with some phytochemicals like lycopene in tomatoes and beta-carotene in carrots. Here are a few examples of classes of phytochemicals, their best sources and their health benefits.

·     Carotenoids which include beta-carotene, lycopene, lutein, and zeaxanthin are found in red, orange and green vegetables and fruit,and can improve immune response, inhibit cancer cell growth and work as antioxidants. (3,4) These phytochemicals are found in broccoli, carrots, cooked tomatoes, leafy greens, sweet potatoes, winter squash, apricots, cantaloupe, oranges and watermelon. (4,5)

·     Flavonoids such as anthocyanins and quercetin are found in apples, citrus fruit, onions, coffee and tea, and can inhibit inflammation and tumor growth, as well as aid in immunity. (5)

·     Cherries, citrus fruit peel and rosemary contain terpenes that can strengthen immune function. (5)

·     The bran of corn oats, rye, rice and wheat, as well as in nuts and soybeans contain inositol (phytic acid), which has antioxidant properties and can retard cell growth. (5)

·     Indoles and glucosinolates, such as sulforaphane are found in cruciferous vegetables like broccoli, cauliflower, kale and Brussels sprouts and can limit production of cancer related hormones and prevent tumor growth. 

·     Cruciferous vegetables also contain isothiocyanates, which can detoxify carcinogens, block tumor growth and work as antioxidants. (3,5)

·     Green tea, grapes, berries, citrus fruit, apples, whole grains and peanuts contain polyphenols which have been found to prevent inflammation and fight viruses. Curcumin is a polyphenol found in turmeric, a medicinal food that has been used for centuries. (5)

Getting Your Phytochemicals

While there are currently numerous clinical trials involving phytochemicals and their health benefits, plant-based foods are complex mixtures of phytochemicals making information on the potential health effects of individual phytochemicals limited. (4) You can make sure your diet is rich in phytochemicals by eating a wide variety of colorful vegetables and fruit, between 2 ½ to 6 ½ cups per day depending on your weight and activity level. (1) For highest phytochemical content, choose produce that is in season, pick deeper colors and more pungent flavors. (3) And stick to food sources. Phytochemicals in supplement form may not be as easily absorbed as their natural counterparts. (5)



1. 2015-2020 Dietary Guidelines for Americans. Office of Disease Prevention and Health Promotion website. Updated April 11, 2018. Accessed April 11, 2018.

2. Liu RH. Health-promoting components of fruits and vegetables in the diet. Adv. Nutr. 2013;4(3):384s-392s.

3. Xu Z & Howard L. Analysis of Antioxidant-Rich Phytochemicals Accessed April 11, 2018.

4. Phytochemicals. Linus Pauling Institute Oregon State University website. Accessed April 11, 2018.

5. Phytochemicals: the cancer fighters in your food. American Institute for Cancer Research website. Accessed April 11, 2018.