What Are Phytochemicals and What Role Do They Play in Health?

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Plant foods are an abundant source of vitamins, minerals, and fiber, but they also provide a diverse array of phytochemicals. Phytochemicals are compounds that don’t offer nutritional value but are still biologically active in the body. Phytochemicals come in many forms and have confusing names, like flavonoids, carotenoids terpenes, lignans, phenolic acids, and more. You find phytochemicals predominantly in plant foods. These components may partially explain why eating a plant-based diet is favorable for health. Foods that contain phytochemicals include legumes, whole grains, nuts, fruits, vegetables, spices, and herbs.

The largest class of phytochemicals are called polyphenols. It would take years of focused study to get a grip on all of the polyphenols, as there are almost 8,000 different types, many of which haven’t been adequately studied. Polyphenols are broken down into sub-types. One of the most important of these sub-types is the flavonoids. To confuse matters even more, there are subclasses of flavonoids with confusing names, like flavanols, flavonols, flavones, flavanones, and isoflavones. Each varies somewhat in its chemical structure.

You’re probably familiar with, for example, some of the foods that contain flavonoids. Every time you bite into an apple, eat a bowl of kale, munch on citrus fruit, or sip tea, you’re getting a mouthful of flavonoids. Anthocyanins are one type of flavonoid with a deep purple pigment that has anti-inflammatory and antioxidant activity. You find anthocyanins in purple foods, like blueberries and red cabbage. Isoflavones are a bit unusual in that they appear to have mild estrogen-like activity. Some studies suggest these foods may lower the risk of breast cancer by binding to breast cell receptors and blocking the activity of the more potent estrogens. You find isoflavones nuts, beans, and soybean products, like miso, tofu, and tempeh.

Other Types of Phytochemicals

Beyond the flavonoids, other classes of phytochemicals and the foods you find them in are:

·       Lignans – pumpkin seeds, flaxseed, sunflower seeds, whole grains, beans, whole grains

·       Carotenoids – orange & red fruits and vegetables, including carrots, pumpkins, tomatoes, squash, watermelon

·       Phenols – coffee, berries, apples, citrus

·       Terpenes – citrus fruit

·       Saponins – potatoes, tomatoes

·       Phytosterols – vegetable oils

·       Glucosinolates – cruciferous vegetables, like broccoli, cabbage, etc.

·       Sulfur compounds – garlic, onions, cruciferous vegetables

Do Phytochemicals Have Health Benefits?

With so many types of phytochemicals, it’s hard to generalize about their health benefits. Plants use these chemicals to protect themselves against predators. They’re also responsible for some of the physical properties that plants have, such as their, color, flavor, and aroma. For example, the presence of certain phytochemicals can explain why carrots are orange and why some vegetables taste bitter. It’s likely that some phytochemicals in plants offer health benefits while some may be mildly toxic. But, even toxic phytochemicals in plants may offer indirect health benefits. One theory is that low levels of a toxic plant chemical “irritates” cells enough to turn on the cell’s internal antioxidant defense system. This, in turn, may protect human cells against damage. So, low levels of exposure to mildly toxic plant chemicals actually make cells “stronger” in a sense.

One characteristic that many phytochemicals have in common is antioxidant activity. Cells are constantly exposed to oxygen and this exposure causes reactive molecules called free radicals to form. These free radicals have lost some electrons and are eager to get them back. So, they grab electrons from other structures within a cell, such as a cell membrane, a cell’s DNA, or some other component. This damages that particular structure. Obviously, we don’t want that to happen! But, if there are antioxidants around, they can supply the free radicals with the electrons they so badly need, so the free radicals don’t damage cells.

Anti-Inflammatory Benefits

If a phytochemical can act as an antioxidant, it can also help reduce inflammation. Since we know inflammation is a force behind many chronic health problems, including cardiovascular disease, autoimmune diseases, and cancer, antioxidants can theoretically lower the risk of these diseases. But, it’s not so straightforward. Most of the studies looking at phytochemicals have been carried out in a laboratory setting, using isolated cells and tissues. In some cases, researchers used phytochemicals in a form that’s different than what you find in the human body. Remember, phytochemicals can be modified by the body before they reach cells. Plus, researchers carry out lab studies under a controlled setting, using high concentrations of particular phytochemicals. This isn’t necessarily the way phytochemicals behave in the human body.

Phytochemicals have other potential health benefits as well. As mentioned, lignans and isoflavones have anti-estrogen activity and this could lower the risk of some estrogen-driven cancers, although more research is needed. Also, of interest is the properties of sulfur phytochemicals, especially those found in garlic. Various studies suggest that these compounds may have a variety of benefits, including the ability to lower blood pressure, reduce the formation of blood clots, and lower lipid levels in the blood. So, phytochemical potentially have a diverse array of positive benefits.

How Strong is the Evidence?

It’s hard to study the direct effects of phytochemicals in the human body since the body is more complicated than isolated cells and tissues. However, research looking at links between eating foods that contain lots of phytochemicals and the risk of disease suggest that a varied diet that contains phytochemical-rich, plant foods may lower the risk of certain health issues. For example, we know that diets rich in fruits and vegetables is correlated with a reduced risk of hypertension, stroke, cardiovascular disease, and some cancers. But, we can’t say whether it’s the vitamins, minerals, and fiber in these foods, the absence of other dietary components (such as meat), or the phytochemicals that play the strongest role.

One caveat: Get phytochemicals from whole plants rather than supplement form. Studies where subjects supplement with an isolated phytochemical fail to show the benefits that come from eating whole, plant-based foods. So, help yourself to another serving of vegetables!



International Journal of Epidemiology, Volume 46, Issue 3, 1 June 2017, Pages 1029–1056,
Today’s Dietitian. Today’s Dietitian. Vol. 15 No. 9 P. 70.
Advanced Nutrition and Human Metabolism. Sixth Edition. Wadsworth Cengage Learning.  2013.


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