Nutrient Superstars:
Phytochemicals These antioxidants pack a mean disease-fighting punch
If somebody asked you to name ten vitamins and minerals and some food sources of them, you probably could do it. (We'll take your word.) And you understand fiber--what Grandmother called roughage. But as scientists study the beneficial, biologically active components of foods, they have uncovered a lot besides vitamins, minerals, and fiber.
Phytochemicals, meaning "plant chemicals," are the big news now. More than 4,000 have been identified. One huge class is the polyphenols, which include the now-celebrated flavonoids. These come in many forms and, true to their name, are often flavorants, such as the allicin in garlic. Sometimes they are pigments, like the anthocyanidins that make cherries red and blueberries blue. Another category is the carotenoids, also pigments, adding color to tomatoes, carrots, and a host of other foods. Beta carotene, for instance, is an orange/yellow pigment that your body uses in its original form and also turns into vitamin A. Phytochemicals often give foods their distinctive smells and flavors. Limonoids, for example--there are 40 of them--give citrus fruits their underlying bitter, citrus-y taste.
The first job of phytochemicals is to benefit the plants. Some phytochemicals are antioxidants--that is, they protect cells from damage by free radicals, which are by-products of the processing of oxygen in living organisms. Like people, plants need antioxidants to survive in our oxygen-rich environment. Plant antioxidants stabilize cell chemistry and protect plants from the damaging effects of oxygen, sunlight, and other factors. We, in turn, can use many of these antioxidants in the same way.
Some phytochemicals not only act as antioxidants, but also help prevent the formation of cancer-causing chemicals and/or suppress cancer development. Others may lower the risk of heart disease by reducing inflammation, inhibiting blood clots, or preventing the oxidation of LDL ("bad") cholesterol.
Some plant chemicals act as pesticides for the plants, fending off or killing fungi, bacteria, and viruses. Some of these may also be toxic to humans.
It would be naive to think that simply because they are natural, all phytochemicals have positive effects. Edible plants can contain bad phytochemicals, which may, for instance, promote cancer in humans. As with many other things in nature, potential negatives may come in the same package with positives.
How to get the most phytochemicals
The versatility of phytochemicals is one reason we keep advising that you base your diet on fruits, vegetables, and whole grains. Choose deeply colored foods whenever you can--they are always rich in phytochemicals. But don't forget the paler foods, such as garlic, onions, cauliflower, and celery. Tea has important and possibly health-promoting phytochemicals; coffee probably does, too, since it is made from a bean. You may wonder whether cooking and other forms of processing reduce phytochemicals, as they reduce vitamin C and some other vitamins. The answer is that this does not appear to be a problem. Indeed, cooking may boost the phytochemical content (as with the lycopene in cooked tomatoes). Still, it's always a good idea not to overcook vegetables and to cook them in a minimum of water.
Bioactivity index
Scientists have come up with different scales for rating the antioxidant capabilities of fruits and vegetables. For instance, researchers from Cornell University have devised the "bioactivity index," taking into account not only antioxidant activity, but also the ability to suppress cancer cells. Here's how the fruits they studied measured up in order of bioactivity: cranberries, apples, lemons, strawberries, red grapes, peaches, bananas, grapefruits, pears, and oranges. Among vegetables, spinach took the lead, followed by red peppers, broccoli, cabbage, carrots, and onions. Among grains, corn was the winner, followed by wheat, oats, and rice.
A phyto-cornucopia
Thousands of phytochemicals have been identified, a huge number of them categorized as polyphenols. The list below calls out just a few, with their most abundant food sources. Many of these have potential antioxidant, anti-cancer, and cardio-protective effects.
Indoles: Cruciferous vegetables, such as broccoli, cabbage, kale.
Isothiocyanates (such as sulforaphane): Cruciferous vegetables
Phytosterols: beans, cucumbers.
Allyl sulfides and other organosulfurs: Garlic, onions, leeks.
Saponins: Garlic, onions, licorice, legumes, nuts, whole grains.
Protease inhibitors: beans, many grains.
Monoterpenes (including limonoids): Oranges, lemons, grapefruit.
Capsaicin: Chili peppers.
Carotenoids (lycopene, beta carotene, etc.): Orange, red, yellow fruits, many green vegetables.
Polyphenols
Flavonoids
Isoflavones: legumes, licorice
Catechins: Tea.
Anthocyanidins: Red, blue, and purple plants, such as eggplant, blood oranges, blueberries.
Quercetin: Apples, onions, tea, citrus.
Naringenin/hesperetin: Citrus.
Phenolic acids (ellagic acid, gallic acid, etc.): Strawberries, raspberries, grapes, apples.
Lignans: Flaxseed, berries, whole grains, licorice.
Resveratrol: Grapes, wine, peanuts.
Last words:
Think of phytochemicals as a health bonus in foods you are already eating for their nutritional value and good taste. But be wary of phytochemicals in supplements. The same compounds that are healthful when supplied by foods may not be beneficial when put in pills.
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