What Are Phytochemicals?

Phytochemicals are compounds that are produced by plants ("phyto" means "plant"). They’re found in fruits, vegetables, grains, beans, and other plant foods. Phytochemicals help to protect plants against disease. While no diet can prevent breast cancer, studies suggest that eating a diet rich in phytochemicals may help:

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  strengthen the immune response (1)

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  protect healthy cells (2)

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  kill unhealthy cells (3)

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  block the activity of cancer-causing agents (also called carcinogens) (4)

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  regulate hormones (5)

It’s important to know that much of the evidence on the effects of phytochemicals comes from observing people who eat mainly plant-based diets. These people appear to have markedly lower rates of certain types of cancers and heart disease. 

While more research is needed to determine if phytochemicals can help reduce the risk of cancer or complement cancer treatment, studies suggest that adding more phytochemicals to your diet is a wise step to take for your overall health. 

Nutrition researchers estimate that more than 4,000 phytochemicals have been identified, but only about 150 have been studied in depth. 

Let’s look at a few with significant research behind health claims:

Flavonoids are found in many grains, vegetables, and fruits. Research suggests that flavanoids help protect against damage to genetic material and proteins in cells.

Isoflavones are a type of flavonoid called a phytoestrogen that are found in high amounts in soybeans and other soy foods like tofu, miso, and tempeh. They are similar in structure to the hormone estrogen and bind to estrogen receptors. Phytoestrogens may block estrogen from binding to estrogen receptors on cancer cells, slowing cell growth.

In a study of thousands of women from around the world, the researchers found that women who consumed more soy (and isoflavones) had a lower risk of breast cancer than those who had less soy in their diets.

Anthocyanins are a type of flavonoid found in fruits and vegetables such as red and purple berries, grapes, apples, plums, and purple cabbage. Studies suggest anthocyanins block the growth of cancer cells.

Catechins are flavonoids found in green tea. Tea catechins, such as EGCG and ECG, may block cancer cells from growing and trigger cell death.

Carotenoids are found in bright yellow, red, and orange colors in plants, vegetables, and fruits such as mangoes, cantaloupe, oranges, yams, and carrots. A study of more than 43,000 women found that those with more carotenoids in their blood were at a lower risk of breast cancer, particularly more aggressive cancers. 

Beta-carotene is found in orange and yellow fruits and vegetables (and beta-carotene pigments give them their color!). It is a type of carotenoid that converts into vitamin A in the body. One study found that breast cancer was less common in premenopausal women with more beta-carotene in their diet than those with less beta-carotene in their diet. The same was not found for women who had gone through menopause.  

Polyphenols are found in coffee, tea, herbs, spices, and more. Types of polyphenols include resveratrol, found in red wine, and ellagic acid in berries. Research has shown that polyphenols help protect the body from molecules called free radicals, which can cause disease, including cancer.

One polyphenol, daidzen, is found in high concentrations in soy foods.

Isothiocyanates are found in cruciferous vegetables such as cabbage, cauliflower, and kale. The highest quantities of isothiocyanates are found in broccoli, especially broccoli sprouts. Many studies have shown that eating cruciferous vegetables reduces the risk of cancer development. Moreover, a large body of evidence shows isothiocyanates help block the formation of tumors.

Because these phytochemicals are in many fruits, vegetables, beans, and grains, eating more whole foods is the best way to get the benefits of phytochemicals. 

There will never be just one vital food ingredient that you need to include in your diet, and no one food or diet alone can prevent breast cancer. Registered dietitians and other healthcare professionals will always recommend eating a balanced diet that includes a variety of vegetables, fruits, legumes, and whole grains. Be wary of any diet that claims it can cure cancer.

There is no evidence that taking phytochemical supplements is as good for you as eating whole fruits, vegetables, beans, and grains that contain them. Most experts strongly believe that it's the combination of these compounds and the other foods you eat that keep your body healthy. 

Loading up on one or two phytochemicals in pill form probably won't be as beneficial as eating a balanced diet with a variety of foods that includes five or more cups of fruits and vegetables per day and food from other plant sources, such as whole-grain breads, cereals, nuts, seeds, rice and pasta, and beans.

Talk with your doctor about dietary supplements that may be more beneficial for you. 

It’s possible to get too much of a good thing. One study found that high doses of the isoflavone daidzein stimulated the growth of estrogen receptor-positive breast cancer cells. 

Talk to your doctor before you make significant changes to your diet.