It is widely known that a diet rich in vegetables, fruits, legumes, and whole grains reduces the risk of cancer, heart disease, and other illnesses. Plants are rich in phytochemicals, which are chemicals that can have antioxidant or hormone-like actions and are associated with many health benefits. Fruits, vegetables, and whole grains can contain thousands of these compounds, which give them their color, aroma, and flavor. Because phytochemicals are often color-specific, similarly colored foods, such as carrots and sweet potatoes, often contain similar types of phytochemicals—hence the recommendation to “eat a rainbow” of foods to ensure the consumption of a variety of phytochemicals.

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It is not yet possible to pinpoint a single phytochemical-powered bullet against cancer or cardiovascular disease, however. The sheer number of phytochemicals in plants, the complexity of the chemical processes in which they are involved, the way the chemicals interact, and the way they are processed by the body all make it difficult to find out which phytochemicals in foods may fight cancer and other diseases, which may have no effect, and which may even be harmful.

Although there are many types of phytochemicals, polyphenols are the most abundant and diverse phytochemicals in our diet. Found in a wide variety of foods, polyphenols are particularly rich in berries, coffee, tea, red wine, cocoa powder, nuts, and spices; numerous fruits and vegetables are also good sources.

Many polyphenols have anti-inflammatory effects, and diets rich in polyphenols are associated with a reduced risk of chronic diseases such as cardiovascular disease, diabetes, osteoporosis, and neurological-related disorders. And polyphenols may reverse, suppress, or prevent the development of cancer. There are thought to be many mechanisms of action—for example, polyphenols may be able to interrupt or reverse cancer development by interrupting cellular communication systems, thus stopping the initiation or promotion of cancer. Some polyphenols can also trigger cell death (apoptosis) in cancer cells. (INFOGRAPHIC 9.4)

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Question 9.4

Resveratrol is a polyphenol found in grapes and red wine. Resveratrol has received attention because animal studies have suggested the compound lengthens lifespan. Some people surmise that it might be responsible for the “French paradox,” the fact that the French, who consume many rich and high-fat foods but drink a lot of red wine, tend to die less often of coronary heart disease than individuals from other Western countries. More research is necessary as wine and other dietary sources of resveratrol may not provide the health benefits suggested, or the benefits may stem from other chemical constituents.

Polyphenols are divided into several chemical classes, with flavonoids being the most abundant. Flavonoids are further divided into subclasses, including anthocyanins (abundant in berries), isoflavones (abundant in soy products and licorice), and flavanols (abundant in dark chocolate and cocoa). Some research suggests that regularly consuming moderate amounts (1 to 2 ounces a day) of dark chocolate may have beneficial effects on blood pressure, insulin resistance, and the risk of cardiovascular disease.

In addition to having antioxidant and anti-inflammatory effects, phytochemicals can also have hormone-like effects. In particular, two groups of polyphenols, isoflavones and lignans (found in flaxseed), are believed to mimic the actions of the female hormone estrogen.

Carotenoids are another important class of phytochemicals. Although more than 700 types of these pigments have been identified, only about 50 of them are common in our diet, where they are responsible for the yellow, orange, and red colors of apricots, watermelons, sweet potatoes, red peppers, and tomatoes. (INFOGRAPHIC 9.5) Some important examples of carotenoids are beta-carotene, lycopene, lutein, and zeaxanthin. Adequate intakes of lutein and zeaxanthin (high in spinach and kale) from food sources have been shown to be important for eye health, while those with high intakes of dietary lycopene (in tomatoes and watermelon) have been seen to have a lower risk of prostate orovarian cancer. Strategies to help you incorporate more phytochemical-rich foods into your diet are included in INFOGRAPHIC 9.6.

Question 9.5

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