By Carol Ann Rinzler

The same plant foods that yield carbohydrates are also the source of phytochemicals — natural compounds other than vitamins manufactured only in plants (phyto– is the Greek word for plant).

Phytochemicals, such as coloring agents and antioxidants, are the substances that produce many of the beneficial effects associated with a diet rich in fruits, vegetables, beans, and grains. The best sources of phytochemicals are highly colored vegetables and fruits.

The most interesting phytochemicals in plant foods are antioxidants, hormonelike compounds, and enzyme-activating sulfur compounds. Each group plays a specific role in maintaining health and reducing your risk of certain illnesses, which is one reason the Dietary Guidelines for Americans urges you to have as many as nine servings of fruits and vegetables and several servings of grains every day.

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 what appear to be potentially carcinogenic (cancer-causing) compounds in your body.

Antioxidants also slow the normal wear and tear on body cells, which may be why so many studies suggest that a diet rich in plant foods (fruits, vegetables, grains, and beans) is likely to reduce the risk of chronic conditions, such as heart disease. But you got to get the plants to get the benefit: Stuffing yourself with antioxidant vitamin supplements shows absolutely no effects on heart health.

Hormonelike compounds

Many plants contain compounds that behave like estrogens, the female sex hormones. Because only an animal body can produce true hormones, these plant chemicals are called hormonelike compounds or phytoestrogens (plant estrogen).

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 soy isoflavones daidzein and genistein, two compounds with a chemical structure similar to estradiol, the estrogen produced by mammalian ovaries. Like natural or synthetic estrogens, phytoestrogens hook onto sensitive spots in reproductive tissue (breast, ovary, prostate, and so on).

These plant estrogenlike compounds are weaker, so researchers once suggested that they might provide postmenopausal women with the benefits of estrogen (stronger bones and relief from hot flashes) without the higher risk of reproductive cancers associated with hormone replacement therapy (HRT). But repeated animal and human studies suggested that, like natural and synthetic hormones, the plant compounds may stimulate tumor growth while having little effect on menopausal symptoms such as hot flashes.

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.”

Sulfur compounds

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

Cruciferous vegetables (the name comes from crux, the Latin word meaning cross, a reference to their x-shape 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 whose aromas are liberated when the food is heated.

Many researchers previously believed that these natural chemicals could tell your body to rev up to fight cancer, but the evidence from multiple studies in the early 2000s, when the cruciferous veggies movement was at its height, is conflicting.

Researchers employ two basic types of studies to assess a link between cause and effect, or in this case, eating cruciferous vegetables and avoiding various forms of cancer. The first type is a case control study, which compares patients with a disease or condition to healthy people, looking back at their histories to see what they may or may not have in common.

The second type is a cohort study, in which researchers establish a base of subjects, say 1,000 women age 25 to 40, and follow them for several years to see whether a specific behavior, such as a diet rich in cruciferous vegetables, will or will not produces a specific effect, such as a lower risk of cancer.

In 2001, a report from a case control study published in the Journal of the American Medical Association showed that eating lots of cruciferous veggies led to a lower risk of breast cancer. But the same year, an overview of a number of studies conducted in the United States, Canada, Sweden, and the Netherlands found no such link.

In 2000, the Netherlands Cohort Study on Diet and Cancer suggested that women — but not men — who ate lots of cruciferous vegetables were at lower risk of colon (but not rectal) cancer. But in 2000, 2001, and 2003, three American and Dutch studies found no link.

From 1992 to 2000, several American and European cohort studies failed to find a definite link between cruciferous vegetables and the risk of lung cancer. One American analysis of data from the long-running Nurses Health Study and the Health Professionals study did show that women — but not men — who ate more than five servings a week were at lower risk.

Some case control studies between 1999 and 2000 suggested that a diet rich in cruciferous veggies might reduce a man’s risk of prostate cancer, but multiple studies in the Netherlands (1998), the United States (2003), and Europe (2004) turned up little or no association.

But then in 2005, a trial conducted in China by researchers from Johns Hopkins Medical School, the University of Minnesota Cancer Institute, and the Qidong Liver Cancer Institute of Jiao Tong University (Shanghai) produced a possible explanation for why cruciferous vegetables might reduce the risk of some forms of cancer.

The sulforaphane in Brussels sprouts inactivates aflatoxins — toxins released by molds on grains, such as rice, that are known to damage cells and, yes, increase the risk of cancers of the stomach and liver, two diseases more common in China than elsewhere in the world. In 2014, researchers from Johns Hopkins School of Medicine, the University of Pittsburgh, and the Qidong (China) Liver Cancer Institute confirmed that sulforaphane produces a cellular reaction that protects against carcinogenic changes. Clearly, this is a subject of interest.

What should you do while waiting for a final answer? Enjoy your phytochemicals. Dig into those veggies, fruits, and grains.