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Phytonutrients: What Are They & Why Are They Important?

Christina L. DiSegna, MS, RD, CSO, CNSC, LDN
Senior Clinical Dietitian
Dana-Farber/Brigham and Women’s Cancer Center

Research indicates that eating a diet rich in plant-based foods, including fruits, vegetables, whole grains, and legumes, is one of the most important pieces for cancer prevention and survival, as well as for overall health. But why are these foods so significant? Evidence is now pointing to the phytonutrient content of these particular food groups.

Phytonutrients are natural chemicals produced by plant foods. Plants use phytonutrients as defense systems against insects, UV rays, disease, and other threats. Some scientists estimate there are thousands – perhaps over 25,000 – phytonutrients found in plant foods. These phytonutrients are also biochemically active in humans and have been shown to provide significant benefits such as antioxidant and anti-inflammatory effects, detoxification, modulation of immune function, and DNA repair. Phytonutrients are not considered essential nutrients for humans as protein, carbohydrates, fats, vitamins, and minerals are but provide significant benefits to those who consume them. Some well-known classes of phytonutrients include polyphenols, carotenoids, flavonoids, omega-3 fatty acids, probiotics, and resveratrol.

Phytonutrients often give plants their pigmentation so an easy way to identify phytonutrient-rich foods is to choose colorful fruits and vegetables frequently. The diverse colors of fruits and veg-etables are often due to different phytonutrient compounds so a variety of different colors in the diet throughout the day and week can optimize phytonutrient intake. Aim to fill half of your plate with fruits and vegetables at each eating opportunity with goal of 5-10 servings each day. Cruciferous vegetables, such as broccoli, cauliflower, Brussels sprouts, kale, and cabbage have additional benefit as one of their phytonutrients helps aid in detoxification of carcinogens; this may help prevent cancer by limiting cell damage. Thus, including at least one serving of a cruciferous vegetable daily is recommended for added benefit.

In addition to fruits and vegetables, spices also have notable phytonutrient activity. Seasoning food with a variety of spices such as turmeric, cilantro, parsley, onions, garlic, and ginger help provide valuable phytonutrients and also make meals much more enjoyable. Similarly, teas, such as green or black tea, also contain phytonutrients and can be a valuable source. Other less colorful phytonutrient-rich foods include nuts, beans and legumes, flax seeds, soy products, and whole grains; these foods should be included regularly as part of a healthy, plant-based diet.

Since these phytonutrients are varied and so important for health, why not take one supplement that includes all of them? Supplements that contain the isolated phytonutrient compound have not shown promising results in a variety of studies and many have shown that there is no benefit as compared with eating the whole food itself. Many scientists believe that this is due to interactions between the phytonutrient compound itself and many other aspects of the plant that provide the health benefit; others feel that it is a combination of many phytonutrients present in the whole plant food that provide the desired result. Regardless of the cause, the best way to maximize the benefit of phytonutrients is to eat a variety of colorful plant foods as opposed to taking supplements.

Diets rich in phytonutrients have shown many health benefits, including cancer prevention and survival. Including a variety of colorful fruits and vegetables, along with other plant-based foods, will provide the greatest benefit over specific dietary supplements. Aiming for half plate of fruits and vegetables at each meal is the easiest way to boost the phytonutrient content in your diet; use the list below for suggestions to get started.

Phytonutrient-Rich Foods

Aim for 5-10 servings per day

  • One serving =
    • 1 cup leafy greens, berries or melon
    • 1/2 cup of other fruits/vegetables
    • 1 medium piece of fruit/vegetable
      (such as apple or tomato)

Cruciferous vegetable*


Apples / Cherries / Tomatoes / Beets / Red Peppers / Red Grapes / Raspberries / Strawberries / Pomegranate / Watermelon / Cranberries / Radishes*

Yellow & Orange

Banana / Cantaloupe / Carrots / Lemon / Mango / Oranges / Papaya / Peaches / Pumpkin / Butternut or Acorn Squash / Spaghetti Squash / Sweet Potatoes / Tangerine / Turmeric


Asparagus / Avocados / Bok Choy / Broccoli / Brussels Sprouts / Cabbage* / Cilantro / Collard Greens* / Leafy Greens / Kale* / Kiwi / Lettuce / Parsley / Peppers / Spinach / Artichokes

Blue & Purple

Blackberries / Blueberries / Eggplant / Plums


Cauliflower* / Onions / Garlic / Ginger / Flaxseed


Teas / Legumes / Nuts / Beans / Soy Products / Whole Grains


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