Just when you think you have a handle on a big issue like nutrition, the Folks in Charge of Everything toss something new on the table. I thought I included something about every aspect of food and health in the first edition of Nutrition For Dummies. Then a new word started showing up in nutrition articles and reports.

The word is phytochemicals, a five-syllable mouthful meaning chemicals from plants. In addition, I thought it was so interesting that I wrote an entirely new article on the subject for NFD/2E (which is what my editor calls the second edition) and NFD/3E.

Now here we are in NFD/ 4E, and by golly, finding a nutrition junkie who hasn’t heard of phytochemicals is difficult. But what people are hearing has turned around a bit.

Phytochemicals (chemicals manufactured only in plants) are the substances that produce many of the beneficial effects associated with a diet that includes lots of fruits, vegetables, beans, and grains. This article gives you a brief summary of the nature of phytochemicals, tells where to find them, and explains how they work.

Did you take French literature in high school or college? If your answer is no, you may as well skip to the third sentence in the paragraph that follows. But if your answer’s yes, then you’re probably familiar with Molière’s The Bourgeois Gentleman.

The bourgeois gentleman is a lovable but pompous character who’s surprised to discover he’s been speaking prose all his life without knowing it.

Your relationship with phytochemicals is probably something like that. You’ve been eating them all your life without knowing it. The following are all phytochemicals:

• Carotenoids, the pigments that make fruits and vegetables orange, red, and yellow (dark green vegetables and fruits like kiwi contain these pigments, too, but green chlorophyll masks the carotenoids’ colors)

• Thiocyanates, the smelly sulfur compounds that make you turn up your nose at the aroma of boiling cabbage

• Daidzein and genistein, hormonelike compounds in many fruits and vegetables

• Dietary fiber

These and other phytochemicals, such as vitamins (yes, vitamins), perform beneficial housekeeping chores in your body. They:

• Keep your cells healthy
• Help prevent the formation of carcinogens (cancer-producing substances)
• Reduce cholesterol levels
• Help move food through your intestinal tract

The undeniable value of phytochemicals is one reason the U.S. Department of Agriculture/Health and Human Services Dietary Guidelines for Americans urges you to have at least five servings of fruits and vegetables and several servings of grains every day.

Did you notice that no minerals appear in the list of phytochemicals? The omission is deliberate. Plants don’t manufacture minerals; they absorb them from the soil. Therefore, minerals aren’t phytochemicals.

Different Kinds of Phytochemicals

The most interesting phytochemicals in plant foods appear to be antioxidants, hormonelike compounds, and enzyme-activating sulfur compounds. Each group plays a specific role in maintaining health and reducing your risk of certain illnesses.

Antioxidants

Antioxidants are named for their ability to prevent a chemical reaction called oxidation, which enables molecular fragments called free radicals to join together, forming potentially carcinogenic (cancer-causing) compounds in your body.

Antioxidants also slow the normal wear-and-tear on body cells, so some researchers noted that a diet rich in plant foods (fruits, vegetables, grains, and beans) seems likely to reduce the risk of heart disease and maybe reduce the risk of some kinds of cancer.

For example, consuming lots of lycopene (the red carotenoid in tomatoes) has been linked to a lower risk of prostate cancer — as long as the tomatoes are mixed with a dab of oil, which makes the lycopene easy to absorb.

However (you knew this was coming, right?), recent studies show that although a diet rich in fruits and veggies is healthful as all get-out, stuffing yourself with the antioxidant vitamins A and C has ab-so-lute-ly no effect on the risk of heart disease.

Hormonelike compounds

Many plants contain compounds that behave like estrogens, the female sex hormones. Because only animal bodies can produce true hormones, these plant chemicals are called hormonelike compounds or phytoestrogens (plant estrogen). Seems fair. The three kinds of phytoestrogens are:

• Isoflavones, in fruits, vegetables, and beans
• Lignans, in grains
• Coumestans, in sprouts and alfalfa

The most-studied phytoestrogens are the isoflavones known as daidzein and genistein (found in soy), two compounds with a chemical structure similar to estradiol, which is the estrogen produced by mammalian ovaries.

Like natural or synthetic estrogens, daidzein and genistein hook onto sensitive spots in reproductive tissue (breast, ovary, uterus, prostate) called estrogen receptors. But phytoestrogens have weaker estrogenic effects than natural or synthetic estrogens.

It takes about 100,000 molecules of daidzein or genistein to produce the same estrogenic effect as one molecule of estradiol. Every phytoestrogen molecule that hooks onto an estrogen receptor displaces a stronger estrogen molecule.

As a result, researchers suggested that consuming isoflavone-rich foods such as soy products may provide post-menopausal women with the benefits of estrogen (stronger bones and relief from hot flashes) without the higher risk of reproductive cancers (of the breast, ovary, or uterus) associated with hormone replacement therapy (HRT).

The theory was supported by the fact that the incidence of breast and uterine cancer, heart disease, osteoporosis, and menopausal discomfort is lower in countries where soy — a primary source of phytoestrogens — is a significant part of the diet.

However, recent animal and human studies offer conflicting evidence. On the one hand, these studies:

• Raise questions about the safety of phytoestrogen-rich foods for women with hormone-sensitive tumors

• Show that phytoestrogen may stimulate tumor growth in animals whose ovaries have been removed

• Demonstrate that isoflavone-rich foods have only modest effects on preserving bone and relieving “hot flashes” at menopause

One the other hand, including isoflavone-rich soy foods such as tofu, miso, tempeh, soy milk, soy flour, and soy protein in a healthful diet:

• May reduce total cholesterol, lower LDL (“bad cholesterol”), and maintain or even increase blood levels of HDL (“good cholesterol”). In 2005, researchers at the Johns Hopkins University School of Nursing announced the results of a 216-woman study funded by the National Heart, Lung, and Blood Institute in which women consuming 20 grams of soy proteins per day had significant decreases in LDLs, while women who were given the same amount of milk protein did not.

• Helps people feel full longer so they can stick to a lower-calorie diet for managing weight loss.

Bottom Line? According to the International Food Information Council, “Further clinical studies will continue to increase understanding of the role of soy in maintaining and improving health.” Couldn’t have said it better myself.

Sulfur compounds

Slide an apple pie in the oven, and soon the kitchen fills with a yummy aroma that makes your mouth water and your digestive juices flow. But boil some cabbage and — yuck! What is that awful smell? It’s sulfur, the same chemical that identifies rotten eggs.

Cruciferous vegetables (named for the Latin word for “cross,” in reference to their x-shaped blossoms) — such as broccoli, Brussels sprouts, cauliflower, kale, kohlrabi, mustard seed, radishes, rutabaga, turnips, and watercress — all contain stinky sulfur compounds, such as sulforaphane glucosinolate (SGSD), glucobrassicin, gluconapin, gluconasturtin, neoglucobrassicin, and sinigrin, that seem to tell your body to rev up its production of enzymes that inactivate and help eliminate carcinogens.

These smelly sulfurs may be one reason why people who eat lots of cruciferous veggies generally have a lower risk of cancer. In animal studies at Johns Hopkins University School of Medicine, rats given chemicals known to cause breast tumors were less likely to develop tumors when they were given broccoli sprouts, a food that’s unusually high in sulforaphane.

In 2005, a human trial conducted in China by researchers from Johns Hopkins, Qidong Liver Cancer Institute, Jiao Tong University (Shanghai), and the University of Minnesota Cancer Center showed that the sulforaphane-rich sprouts appear to help the body defang aflatoxins produced by molds that grow on grains such as rice.

Aflatoxins, which damage cells and raise the risk of cancer, may be linked to the high incidence of stomach and liver cancer in China. Further studies are in the planning phases.

Dietary fiber

Dietary fiber is a special bonus found only in plant foods. You can’t get it from meat or fish or poultry or eggs or dairy foods. Soluble dietary fiber, such as the pectins in apples and the gums in beans, mops up cholesterol and lowers your risk of heart disease.

Insoluble dietary fiber, such as the cellulose in fruit skins, bulks up stool and prevents constipation, moving food more quickly through your gut so there’s less time for food to create substances thought to trigger the growth of cancerous cells.