Fruits and vegetables, whole grains, nuts, beans, seeds – yes, there are reasons why you’re constantly being told to eat them. They’re healthy! And one of the key elements that makes these foods healthy is a group of compounds called .

What are phytochemicals?

Phytochemicals are biologically active, non–nutrient compounds naturally occurring in plant foods (e.g., fruits, vegetables, grains, beans, nuts, seeds). The word “phyto” is taken from the Greek word meaning plant. So phytochemicals are plant chemicals. Antioxidants are a particular kind of phytochemical with specific properties that have been found to protect humans against disease. All types of phytochemicals are nature’s way of protecting plants from disease and thus increasing their survivability. They affect humans in a variety of ways — from imitating hormones (e.g., phytoestrogens) to altering blood ingredients in ways that may protect against some diseases.

According to Karen Collins, M.S., R.D., C.D.N., nutrition adviser to the American Institute for Cancer Research, there are two key concepts to understand about phytochemicals. “First, different plant foods contain different phytochemicals, each of which seems to act in slightly different ways on parts of cells. So to get the widest array of benefits, eating a variety of plant foods is important. And second, phytochemicals seem to work best in combination with one another. So even though you can get some particular phytochemical that you hear about as beneficial in supplement form, current research suggests that it will not function the same way when taken in isolation as it does when consumed as part of a food and a plant–based diet supplying a host of other phytochemicals.”

What is the difference between an antioxidant and a phytochemical?

According to Victoria J. Drake, Ph.D., a research associate at the Linus Pauling Institute at Oregon State University: “Some, but not all, phytochemicals have been shown to exhibit antioxidant activity. For example, flavonoids, which are found in tea, red wine, fruits, vegetables and legumes, are effective antioxidants in the test tube.”

So there is both a difference and an overlap between the two terms. All antioxidants are phytochemicals but not all phytochemicals are antioxidants. Most phytochemicals being studied for health reasons do function as antioxidants, but many serve additional functions that are unrelated to their role as antioxidants.

Are phytonutrients the same as phytochemicals?

According to Collins: Currently, the terms “phytonutrient” and “phytochemical” are being used interchangeably to describe those plant compounds that are thought to have health–protecting qualities. Technically, though, the term phytochemical often refers specifically to compounds in plant foods that are biologically active in terms of promoting health but are not essential nutrients. (So, for example, the folate and vitamin C found in plant foods are phytonutrients rather than phytochemicals.)

How do phytochemicals fight disease? What’s the relation to fighting cancer?

Many phytochemicals are antioxidants, and antioxidants seem to protect against many chronic diseases (heart disease, cancer, metabolic syndrome, diabetes and more). “However, exciting research continues to identify pathways through which phytochemicals impact health that seem to be outside their role as antioxidants. For example, some phytochemicals seem to stimulate enzymes that deactivate carcinogens before they can cause the initial cell damage that can begin the process of cancer development, while others can ‘turn on’ tumor–suppressor genes (through what are called epigenetic modifications) that trigger already–formed cancer cells to stop dividing and self–destruct,” says Collins.

Would you say that industrially processed foods are likely to contain fewer phytochemicals than unprocessed foods and that these foods may, therefore, be less beneficial?

Unprocessed foods such as vegetables and fruits in their natural state, 100 percent whole grains, nuts and beans contain more protective phytochemicals. When a food is processed, most times it’s stripped of many of these protective phytochemicals.

Can you explain the importance of bioavailability of phytochemicals?

“To be effective, a phytochemical generally needs to be absorbed by the cells of our body. So effects seen in test tube studies don’t necessarily show what a phytochemical will do in our bodies,” says Collins. For instance, a lab study might use grapes in much larger quantities than we would ever consume or absorb in order to show their ability to prevent disease.

“We also now are learning that the same phytochemicals may be more bioavailable to some people than others — because of differences in absorption and because of genetic differences in how quickly the compounds are metabolized and excreted. That would be one reason why different research studies sometimes seem to provide differing results,” adds Collins.

What do colors have to do with phytochemicals?

Many phytochemicals are pigments that give plant foods their color. For example, lycopene is red, and several other carotenoids (i.e., beta carotene) are deep orange.

Can you get them from a pill?

Large doses of purified phytochemicals added to foods may produce effects vastly different from those of phytochemicals in whole foods.

Phytochemicals in Action

Allyl sulfides: Foods such as onions, garlic, scallions and chives contain compounds called allyl sulfides. Although mainly known for making your eyes water, allyl sulfides are believed to enhance immune function, inhibit tumor growth, facilitate carcinogen excretion and reduce serum cholesterol levels.

Glucosinolates: Broccoli, cabbage, Brussels sprouts, cauliflower, watercress, turnips and cabbage are not only loaded with vitamins and minerals but also contain phytochemicals called indoles and isothiocyanates, collectively called glucosinolates. These compounds have been shown to trigger enzyme systems that eliminate carcinogens from the body and to increase the expression of genes that suppress tumor development. They also appear to reduce tumor size and work against the high levels of estrogen associated with breast cancer. However, the long–term effects of indole–3–carbinol supplementation on cancer risk in humans are not known.

Carotenoids: The most famous of all the phytochemicals, carotenoids such as alpha and beta carotene are pigments that give many fruits and vegetables their vibrant color. They also seem to be antioxidants that help offset the damage done by oxidation, a normal metabolic process that can leave the body vulnerable to cancer, heart disease, macular degeneration and accelerated aging. Food sources include dark–green, orange or red fruits, and vegetables such as carrots, sweet potatoes, spinach and broccoli. Lycopene, another famous carotenoid found in tomatoes, appears to play a powerful role in preventing prostate cancer. More recently, it has also been shown to help prevent stomach cancer.

Phytoestrogens: Soy foods, especially tofu, tempeh and miso, contain phytoestrogens that may protect against certain cancers, particularly hormone–sensitive cancers such as those of the breast, endometrium and prostate. Phytoestrogens such as genistein, daidzein and lignans, interfere with sex hormone metabolism, which often goes awry in these types of cancers. However, some recent studies done on animals and with test tube cultures suggest that phytoestrogens may actually stimulate growth of breast cancers that are estrogen–sensitive. More research is needed to clarify the effects of phytoestrogens on breast cancer. Phytoestrogens have also been associated with reducing bad (LDL) cholesterol levels.

Polyphenols: Polyphenols include ellagic acid, tannic acid, vanillin, caffeic, chlorogenic and ferulic acid. Found in almost all plant foods but especially strawberries, raspberries, blackberries, walnuts and pecans, polyphenols are thought to prevent the conversion of substances into carcinogens and to inhibit cell mutations.

Flavonoids: Flavonoids are polyphenolic compounds found in fruits, vegetables, wine, tea and chocolate that exhibit antioxidant activity. These pervasive substances may defend cells against carcinogens, curb the oxidation of LDL cholesterol and prevent blood clotting.

Phytosterols: Phytosterols bind cholesterol in the gut and inhibit its absorption into the blood. Sources include unrefined vegetable oils, whole grains, nuts and legumes.

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