In This Chapter
The word phytonutrient comes from the Greek word for plant, phyto, and means “plant nutrients.” These are additional chemical substances that offer your body a protective health benefit and help ward off disease. They’re different from vitamins and minerals, but can act in a similar way.
Many phytonutrients are known to exist and scientists believe there are many more that haven’t even been identified. However, research suggests there’s strong evidence that phytonutrients provide a myriad of health benefits. At this time, there isn’t enough research to make specific recommendations on consumption of daily amounts as with vitamin and minerals.
In this chapter, you’ll learn about some of the more common phytonutrients and their potential health roles. We’ll also discover which foods provide the best source for each of the phytonutrients.
A phytonutrient is a naturally occurring, biologically active, plant-based chemical found in all plants. It’s what helps protect the plant from insects, sun damage, and disease. When we eat plants like fruit, vegetables, whole grains, herbs, and spices, we ingest those plant nutrients. Many of these active plant compounds are what give the plant its distinct color, such as carotenoids, which make carrots orange. They can also be responsible for the flavor and aroma, as with allicin in garlic and onions.
A phytonutrient is also referred to as a phytochemical, and the terms are used interchangeably. Thousands of phytonutrients exist, but only a fraction of them have been studied. Researchers have determined that some of the compounds are best consumed raw and others are more bioavailable when cooked, as is the case with lycopene in tomatoes.
Bioavailability refers to an active chemical compound being physiologically available for use in the body.
Phytonutrients have been used as medicine for centuries, but people didn’t understand the why a certain food aided in the healing process. Scientists can now identify specific plant chemicals like lycopene and study the effects in the body or under the microscope. They also can define the compound’s mode of action on specific cells in the body, such as cancerous cells.
One of the primary roles of phytonutrients is to act as antioxidants. Ongoing research is looking at the role of these plant chemicals in relation to heart disease, diabetes, cancer, and neurological diseases like Alzheimer’s.
Phytonutrients are divided into three groups based on their molecular structure: phenolic acids, flavonoids, and stilbenes/lignans. Flavonoids are the largest group, and are subdivided into anthohcyanins, flavones, flavanones, isoflavones, flavonols, and flavanols. Flavonols are subdivided into catechins, epicatechins, proanthocyanidins, procyanidins, and prodelphinidins. A few of the more common phytonutrients we’ll review in greater detail have been substantially researched. They are anythocyanins, lycopene, resveratrol, carotenoids, phytoestrogens, lutein, and allicin.
The Benefits of Phytonutrients
Researchers became interested in phytonutrients because they noticed a trend in epidemiological studies involving cancer and heart disease. They found that people who ate more plant-based foods tended to be healthier, have less disease, and live longer. This led them to look at the foods and their composition. Identifying one single compound and connecting it to a health claim is difficult because there may be hundreds of phytochemicals in one food. In addition, it may not be just that one phytochemical that provides the benefit, but the synergistic action of all of them combined.
One of the most beneficial roles of plant chemicals is to function as an antioxidant. Antioxidants protect your cells from damage from free radicals, which are produced during normal cell metabolism. Free radicals can also come from outside sources, such as radiation, cigarette smoke, and exposure to toxic chemicals.
According to the U.S. Department of Agriculture (USDA), phytonutrients may also support body’s immune response, aid in communication between cells, kill cancer cells, repair DNA, act as a detoxifier, and alter estrogen metabolism. No recommendations for a daily intake exist because further research must be done before any conclusion can be made. Let’s take a look at a few of the key phytochemicals in foods and their potential health benefits.
Carotenoids contain a large subgroup of phytochemicals. Beta-carotene, lycopene, lutein, and zeaxanthin are a few that we’ll discuss a little later. Researchers believe the health benefits from consuming carotenoids are due to their role as an antioxidant. Much research has been done on the role of carotenoids in relation to cancer and eye disease.
Carotenoids include more than 600 plant pigments, but they’re the primary sources for orange, red, and yellow colors found in plants. Beta-carotene is also what gives the color to flamingos, goldfish, salmon, and autumn leaves. Carotenoids are fat soluble, and in order to digest them you need to have a little fat along with your carotenoid-containing food.
Beta-carotene is a phytonutrient, but it’s also the precursor to vitamin A. Your body can split beta-carotene into two molecules of vitamin A, which is an essential nutrient for your body. Beta-carotene was the first phytochemical to be measured in foods, and is found in orange, red, and yellow plant pigments.
The function of beta-carotene is to act as an antioxidant. Research has shown an ingestion of foods high in beta-carotene has aided in the prevention of vision loss due to macular degeneration, decreased the risk of breast cancer, prevented bronchitis, and decreased asthma attacks during exercise. It also has been reported to aid in pain reduction associated with osteoarthritis, decrease ovarian cancer risk, and improve muscle strength in older people.
All of this makes beta-carotene sound like a wonder nutrient. Indeed, it does have many positive effects on health, but adverse effects also have been identified through research. The most famous study is from 1994, The Effect of Vitamin E and Beta Carotene on the Incidence of Lung Cancer and Other Cancers in Male Smokers. In this study, the subjects were males in Finland who were supplemented with 50mg of vitamin E, 20mg of beta-carotene, or a combination of the two. The study included 29,133 male smokers age 50 to 69 years old. Researchers saw an increase in lung cancer in the subjects who were taking beta-carotene. Supplementation was stopped and the men were followed for 5 to 8 years.
After the Finland study, researchers were concerned about the negative impact of beta-carotene use on health. However, in the physician’s health study, which included smokers and nonsmokers, there was no evidence that beta-carotene had an adverse affect even after 18 years of following the participants. In another study, they also reviewed the impact of beta-carotene in an antioxidant cardiovascular study of women. They found there were no beneficial effects of beta-carotene supplementation in relation to cardiovascular risk, nor did it slow age-related cognitive functions or have a negative impact.
Eating too many carrots can turn you orange. Well, actually it’s yellow. This effect is typically seen in young children who can get stuck on only eating one food such as carrots. The color will eventually fade in a couple of weeks’ time once the child stops eating carrots. For an adult, three large carrots per day would exceed recommended vitamin A intake and might make you turn yellow.
Food sources of beta-carotene include sweet potatoes, carrots, cantaloupe, winter squash, apricots, collard greens, kale, and broccoli. Overall, beta-carotene is a powerful antioxidant. The best bet is to consume beta-carotene–rich produce as part of a healthy diet, and you will get the added benefit of phytonutrients.
Lycopene belongs to the carotenoid group, and it functions as an antioxidant, too. Lycopene is a plant pigment that makes vegetables and fruit red. It has been heavily researched and studied in conjunction with the growth of cancer cells, the protective effect on bone health from free radical damage, and in relation to osteoporosis. Researchers report that eating one cup of tomatoes a day will help protect you from sun damage. That’s a great motivation to include two servings of vegetables and prevent premature aging of the skin from sun exposure.
Cooking lycopene-containing foods like tomatoes has a positive effect by increasing the bioavailability of lycopene threefold. Other top food sources for lycopene are red peppers, pink grapefruit, and watermelon.
During colonial times, tomatoes were grown only as ornamental plants. People were afraid they were poisonous because they belonged to the nightshade family of plants, Solanaceae. In fact, the leaves of the tomato plant are poisonous, but the fruit is not.
Lutein and Zeaxanthin
These phytonutrients are being studied in relation to vision because lutein and zeaxanthin can be stored in the retina and lens of the eye. It’s believed that they can help protect your eyes from damaging ultraviolet light.
Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. Therefore, many studies examine the role of lutein in eye health. In the Age-Related Eye Disease (AREDS) study, those who took supplements of lutein and zeaxanthin had a 26 percent reduced risk of developing AMD. However, the researchers did note that those on the supplement did not consume food sources (produce) with those same phytochemicals. If it were not for the supplements, subjects would have never ingested lutein or zeaxanthin.
Additionally, the same study also looked at the effect of beta-carotene supplements opposed to lutein/zeaxanthin supplementation, and there was an 18 percent lower risk of AMD compared to the group who took beta-carotene.
Food sources of lutein and zeaxanthin include collard greens, kale, spinach, broccoli, brussels sprouts, lettuces, artichokes, and eggs. These phytonutrients are what give egg yolks, corn, and avocados their yellow color.
The flavonoids are a large group of phytonutrients and are categorized as polyphenolic compounds. The common flavonoids are anthocyanidins, flavanols, flavanones, flavonols, flavones, and isoflavones. This group of phytochemicals appears to aid in cell-signaling pathways that deal with cell growth and death as opposed to working solely as an antioxidant. Research with the flavonoids has focused on their relation to cardiovascular disease, cancer, and neurodegenerative diseases.
Flavonoids vary in their chemical structure and bioavailability. Some flavonoids are attached to a sugar molecule called flavonoid glycosides. The ones not attached to a sugar molecule are flavonoid aglycones. Flavonoid glycosides are quickly broken down and absorbed in the small intestine. The remaining flavonoids may be broken down in the colon by bacterial enzymes. However, your ability to metabolize the flavonoids may depend on the overall health of your gut bacteria.
Anthocyanidins include the dietary flavonoids cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin. They’re responsible for the red, blue, and purple pigments found in plants. Heat damages and breaks down these pigments, and thus decreases the biochemical activity of the anthocyanidins. It’s a water-soluble molecule and is greatly affected by changes in pH. It can also be damaged by exposure to oxygen and UV light.
Research on anthocyanidins has shown they improved night vision in a study of British soldiers, prevent oxidative damage to the brain by blocking harmful chemicals from receptor sites, and prevent oxidation in LDL cholesterol in blood vessels.
Food sources of anthocyanidins include blueberries, blackberries, plums, cranberries, raspberries, red onions, red potatoes, red radishes, strawberries, beets, purple cabbage, and cherries.
Catechins belong to the flavanol group, which is part of the larger group of flavonoids. Along with the catechins are the flavonoids epicatechin, epigalocatechin, epicatechin gallate, epigallocatechin gallate, theaflavin, and proanthocyanidins.
Chemically the catechins are very stable compounds and not adversely affected by heat or acid. They also have an astringent and bitter flavor.
Catechin is the primary phytonutrient found in tea leaves from the Camellia sinensis plant. Green tea is one of the most consumed beverages in the world. Observational studies have shown that consumption of three cups of tea daily may reduce the risk of heart attacks. One study in The American Journal of Clinical Nutrition reported that Japanese men who drank green tea containing 690mg of catechins lost more weight than the control group. Another very small study of men showed that an extract of epigallocatechin gallate (EGCG) increased the metabolic rate by 4 percent in a 24-hour period, which equated to burning an additional 65 to 200 calories.
The best food sources for catechins include quality green and white tea, cocoa, grapes, berries, and apples.
Isoflavones include the flavonoids daidzein, genistein, and glycitein. Soybeans provide the most isoflavones in the diet. Only small amounts of isoflavones are found in legumes, grains, and vegetables. These phytonutrients are water-soluble, heat-stable, and are bound to sugar molecules and broken down in the small intestine. The bacterial gut flora also aids in the breakdown of the molecules.
Isoflavones have estrogen-like properties and compete for estrogen-binding sites within the cells. This makes sense because the molecular structures of isoflavones are also quite similar to human estrogen.
Research has examined the relationship between isoflavones and breast cancer, prostate cancer, menopausal symptoms, heart disease, and osteoporosis.
In 2006, the American Heart Association (AHA) reviewed 22 studies on the effect of soy protein with isoflavones finding there was only a minimal cholesterol-lowering effect or no benefit at all. Therefore, the AHA doesn’t recommend isoflavone supplementation to prevent heart disease.
The primary food source for isoflavones is soy. There’s approximately 200mg of isoflavones in 3½ ounces of dried soy protein.
One of the most studied stilbenes is resveratrol. Stilbenes are classified as polyphenols, which include phenolic acids, tannins, diferuloylmethanes, and flavonoids. Stilbenes have been shown to have antibacterial and antifungal properties and offer protection against heart disease.
Resveratrol is the phytochemical in red wine. The term “French Paradox” was first used by a French epidemiologist in the 1980s after researchers made the connection between the French people’s high intake of cholesterol and saturated fat along with their high red wine consumption. Theoretically, the French should have a higher death rate from coronary heart disease based on their diets. However, their moderate alcohol consumption has been shown to reduce heart disease risk by 20 to 30 percent. Unfortunately, it’s difficult to determine whether it was the effect of the resveratrol content or flavonoids, which are also present in red wine.
Research has also shown resveratrol to reduce platelet aggregation, decrease blood pressure, and inhibit inflammation, which is important in decreasing the risk of cardiovascular disease.
Food sources for resveratrol include the skin of grapes, red wine, purple grape juice, peanuts, and some berries.
Phytonutrients are broken down in the body according to the molecular structure of the phytochemical. Some phytochemicals are attached to a sugar molecule, which must be split apart. Once split, the smaller molecule can be absorbed by the small intestine. Other phytochemicals, such as beta-carotene and lycopene, require dietary fat to improve absorption because they’re fat-soluble molecules, and must be emulsified by bile in the digestive process. Still others phytonutrients may require a carrier to be transported through the body. Some phytochemicals survive the pH of the stomach intact and others do not, as in the case of allicin.
Microflora in the gut are responsible for breaking down some phytochemicals. An imbalance in this bacterial colony could cause a lesser amount of certain phytochemicals (acids) to be formed. In the colon, some of the acids may be reabsorbed and travel back to the small intestine or the liver, where they’re bound to another molecule before absorption into the blood.
Which Is the Best: Phytonutrient Pills or Whole Foods?
Due to all the variables in phytonutrients—from chemical structure, water-soluble/fat soluble, and damage by exposure to heat and light—it makes sense to get your phytonutrients from whole foods. Scientists are still not sure if certain phytochemicals are independent in action or if there’s a synergistic effect from other plant compounds in the foods.
Another thing to consider is the extraction process of the phytonutrients into supplement form. Does the product you purchase actually contain any of the active ingredients? Has the product been tested by an independent lab to verify its contents? A supplement form may also cause an adverse reaction and be detrimental to health, as in the Finland study with beta-carotene. For example, garlic supplements have been shown to cause GI distress. Your best bet is to eat the whole foods.
Getting More Phytonutrients in Your Diet
There are no government recommendations for consuming specified amounts of phytonutrients because more research must be done in relation to health. However, eating 5 cups of fruits and vegetables daily and making sure half your plate is filled with colorful fruits and vegetables is a good start.
As we learned with some phytonutrients like lycopene, it’s important to eat a variety of cooked and raw foods. The following table provides top food sources and amounts for select phytochemicals.
From the Linus Pauling Institute.
When it comes to phytonutrients, your goal is to eat more fruits, vegetables, and whole grains, and consider adding green tea and cocoa to your diet. Be sure half of your plate is made up of colorful fruits and vegetables.
The following recipe is a good source of phytonutrients.
1 lb. red beets
1 TB. vegetable oil
¼ tsp. kosher salt
1 large jalapeno, seeded and finely chopped
½ red onion, finely chopped
1 TB. lime juice
Zest of 1 lime
¼ tsp. kosher salt
2 TB. cilantro, finely chopped
1. Preheat oven to 400°F. Remove roots and tops from each beet.
2. Peel beets and cut into ¼-inch pieces. Toss beets in oil and salt. Place on baking sheet and roast for 20-25 minutes or until tender. Remove from oven and let cool.
3. Combine cooled beets, jalapeno, red onion, lime juice, lime zest, salt, and cilantro. Mix well. Refrigerate until serving or serve immediately at room temperature.
Cook’s note: Wear disposable gloves when working with red beets to prevent staining. For a spicier dish, use some of the seeds from the jalapeno.