In the late 20th
century, the field of nutrition changed forever with the discovery that plants contain thousands
of bioactive chemicals. Discovering these phytochemicals may prove to be as significant as learning that there are more stars in the universe than those in our night sky. It opened a vast door for the field of nutrition, convincing physicians that disease can truly be prevented through dietary modification. Now that the cat is out of the bag, identifying exactly how
these chemicals interact with each other and the body is the next step. There will be a steady stream of impressive discoveries over the next few decades.
In the last 40 years, researchers began to unravel the role of antioxidants in the body and how they prevent the process of cellular damage called oxidation. The most notable players are vitamin C, vitamin E, the mineral selenium (part of the master antioxidant complex glutathione peroxidase), and beta carotene and all of its siblings - known as the carotenoids. But scientists also uncovered plant compounds in foods with strong antioxidant properties that were neither vitamin nor mineral. Experiments have shown that many of these substances, known as phytochemicals, exert other effects in the body, such as stimulating liver detoxification enzymes or promoting an anti-inflammatory response.
Why do plants produce these phytochemicals that are so beneficial for us? The reality is that plants synthesize phytochemicals to protect themselves against UV light damage, air pollutants, oxidation, bacteria, fungi, insects, and animals. Over the course of evolution, however, humans have developed a symbiotic chemistry with many of these phytochemicals. Bear in mind that many of these compounds will render us sick, silly, or dead. The beneficial ones have been loosely categorized into classes, three of which are described below.
1. Phenols potent antioxidants found in red wine, potatoes, tomatoes, peppers, parsley, squash, yams, celery, carrots, cabbage, soybeans, flaxseed, some nuts, citrus fruits, and garlic. Chocolate, as you’ve heard by now, also contains phenolic activity! Some phenols are able to modify prostaglandin pathways yielding anti-inflammatory and platelet thinning properties.
- Bioflavonoids a family of over 5,000 phytochemicals, are a subclass of phenols. The flavonoids that act as antioxidants, including hesperidin quercetin, rutin, and catechin, are found in the white rind beneath the peel of citrus fruits, as well as in cherries, blackberries, blueberries, apricots, apples, grapes, peppers, soybeans, garlic, onions, and leafy vegetables. Green tea is a source of catechins, a class of compounds that exhibit anti-cancer properties. Isoflavones, particularly daidzein and genistein found in soy products, may also reduce the risk of cancer. Oligomeric proanthocyanidins are potent antioxidants found in grape seeds and pine bark but also in peanuts, cranberries, cherries, plums, and citrus peel.
2. Terpenes a huge class of phytochemicals that function as antioxidants, enhance immune response, and protect the skin against UV light damage.
- Carotenoids, a family of over 500 compounds, are a subclass of terpenes. Notable carotenoids are lycopene and lutein, antioxidants that are being investigated for their ability to reduce the risk of prostate cancer and macular degeneration respectively. Sources of carotenoids include dark green leafy vegetables, carrots, winter squash, sweet potatoes, tomatoes, and watermelon.
3. Thiols a class of phytochemicals that contain sulfur and have an array of effects ranging from stimulating cytokine production (key immune system compounds) to directly blocking enzymes that promote tumor growth. Sources include the cruciferous vegetables (broccoli, bok choy, cauliflower, cabbage, collard greens, kale, brussels sprouts, turnips) and the allylic sulfides discussed below.
- Allylic sulfides, a subclass of thiols, have antioxidant properties, as well as possessing antibiotic and platelet-thinning properties. Best sources include garlic, onions, chives, leeks, and shallots.
These three classes are just the tip of the iceberg. Fortunately, we don’t need to know who they are or how to say their names to reap their benefits we just have to eat them! Eat a whole foods diet and consume a wide variety of at least seven servings of fruits and vegetables daily. Cover your bases with these superstar foods: garlic, onion, soy products, green tea, berries, nuts, cruciferous vegetables, orange and yellow vegetables, whole grains, beans, and tomatoes.
Greg Hottinger, MPH, RD