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The amazing world of phytochemicals: an interview with Victoria J. Drake, Ph.D.

Q: What are phytochemicals?

A: Phytochemicals are chemicals produced by plants. The term is usually used to describe plant derived chemicals that are not required nutrients but that may nevertheless affect health.

Q: Do phytochemicals differ from phytonutrients?

A: I think that some people use the terms "phytochemical" and "phytonutrient" interchangeably. However, I would not consider phytochemicals to be nutrients because they are not known to be essential for health. Those who use the term "phytonutrient" may be referring to the vitamins and nutritionally essential minerals found in plants.

Q: How do phytochemicals differ from vitamins and minerals?

A: Vitamins and some minerals are essential nutrients. However, increasing scientific evidence suggests that some phytochemicals may promote health or prevent human disease.

Q: How do phytochemicals differ from nutraceuticals and functional foods?

A: There seem to be many definitions of nutraceuticals, which can be confusing. I would say a nutraceutical is a food or a component of foods, plants, or other natural material that is claimed to benefit human health. It is marketed as Such. It is a hybrid of the words "nutrition" and "pharmaceutical." Nutraceuticals can be purified and/or concentrated and put in a tablet or pill form or perhaps even a powder. Some phytochemicals can be nutraceuticals. For example, you might see indole-3-carbinol, or beta-carotene, or lycopene supplements. While phytochemicals can be nutraceuticals, nutraceuticals can also include vitamins and minerals, fatty acids, and microbes, such as probiotic supplements for gastrointestinal health. "Nutraceutical" is a general term for anything that is isolated from a naturally occurring material, such as a plant, and marketed as a health supplement.

"Functional foods" generally refer to naturally occurring foods or manufactured food products that have health benefits beyond basic nutrition (vitamins, minerals, and fatty acids required by the body). Although they are similar in appearance to conventional foods, they contain biologically active compounds or components that have been shown to prevent or reduce the risk of chronic disease or to treat human diseases.

Q: What is the history of phytochemicals?

A: I am not sure when people started calling chemicals from plants phytochemicals. However, plants and their compounds have been used since antiquity for various purposes. Ancient Greek and Roman literature reference the use of poisons derived from plants. For instance, Socrates was said to have been executed by using hemlock. Botanical gardens have been used throughout history as a source of medicinal plants. Today, several phytochemicals are on the market as dietary supplements.

Q: Do researchers know how many phytochemicals there are?

A: There are thousands of different phytochemicals and likely ones that have yet to be isolated. I think some estimates reach 10,000. However, high-quality studies are available for only a subset of these phytochemicals.

Q: What are the major groups of phytochemicals?

A: There is no definite way to classify phytochemicals. Some researchers may group phytochemicals based on their endpoint, such as which disease might be affected by a phytochemical. You could group them based on food source or chemical structure or class. However, classifying them can be confusing, because some members can be in more than one class. The major classes are not always the same. I prefer to classify phytochemicals based on chemical structure.

In general, the main groups are:

(1) phenolic compounds, including flavonoids and phytoestrogens;

(2) glucosinolates, found in cruciferous vegetables, such as broccoli;

(3) carotenoids, which include beta-carotene, alpha-carotene, beta- cryptoxanthin, zeaxanthin, lutein, and lycopene; and

(4) the Allium family, which are organosulfur compounds, such as garlic, onions, and leeks.


Q: Which phytochemicals can rid the body of harmful substances?

A: Isothiocyanates stimulate the activity of enzymes that help to remove potential cancer-causing agents. These phytochemicals are found in cruciferous vegetables, such as broccoli, cauliflower, cabbage, and kale.

Q: Do you recommend taking phytochemicals as supplements?

A: I do not think there is enough evidence right now to recommend any specific phytochemical supplement. I recommend the food sources themselves because plant-based foods, including fruits, vegetables, legumes, whole grains, and nuts, are prominent features of a healthy dietary pattern.

There is limited evidence to support health benefits of a specific nutrient or phytochemical. Because the whole food is a complex package of biologically active compounds, the potential health benefits of individual phytochemicals cannot always be separated from the health benefits of the foods that contain them.

In addition to providing phytochemicals, foods also provide energy and essential micronutrients, such as vitamins and minerals. With that said, people with high cholesterol levels may want to consider eating foods that are enriched with plant sterols or stanols, which can lower levels of low-density lipoprotein cholesterol (LDL or "bad" cholesterol).

Q: Do any phytochemicals have the potential to be toxic if taken in large quantities in tablet form?

A: In general, toxicological studies are limited. Certainly, you would have to consider the individual biochemical and the dosage. The main concern for toxicity from phytochemicals would be from dietary supplements that contain the isolated, concentrated phytochemical at 100 or more times the levels seen in the diet.

It is important to keep in mind that just because phytochemicals are "natural," they are not necessarily safe, especially at very high dosages. There have been reports that kava can cause liver toxicity. I would also not recommend taking indole-3-carbinol supplements because we do not know the effects in humans. Another supplement usually thought of as harmless, beta-carotene, may increase lung cancer risk in current smokers, former smokers, and asbestos workers.

Q: Are there any relatively safe phytochemical supplements that are difficult to find in their natural plant form that would be beneficial in tablet form?

A: It is my opinion that there is not enough scientific evidence to recommend phytochemical supplements, except possibly for people with high cholesterol levels who may want to include foods enriched with plant sterols or stanols. Many clinical trials have demonstrated that daily consumption of these foods lowers LDL cholesterol.

For example, plant sterols and stanols are included in certain margarines, low-fat dairy products, dark chocolate, and orange juice. Consumers should check food labels. Doses should be similar to what would be taken in a tablet. More than 2 grams of plant sterols and stanols daily does not seem to add much benefit, and there might be undesirable effects at higher intakes.

Q: Are there phytochemicals that act as antioxidants in the body?

A: You might hear that a phytochemical is an antioxidant. However, several phytochemicals have mainly been studied in vitro (in a test tube). Thus, we do not know whether they appreciably contribute to the body's antioxidant capacity. Flavonoids are extensively metabolized and poorly absorbed, so they are not very bioavailable as antioxidants, even though they are touted as that.

To date, few in vivo studies have been conducted with these compounds. At least for the flavonoids, it is likely that their antioxidant function in humans is small or negligible because of their relatively low bioavailability and their extensive metabolism. (Bioavailability refers to the body's ability to absorb and use the nutrients derived from food.)

Considering that flavonoids are poorly absorbed, we would need an extremely high dose in order to get any antioxidant benefit. Even then, flavonoid concentrations in the body are likely to be more than 100 times lower than concentrations of otherantioxidants, such as vitamin C.

Q: What are some of the challenges in studying diet?

A: It is very difficult, if not impossible, to attribute a health benefit or health effect to a specific phytochemical when you are measuring intake of the whole food. This is partly due to the fact that there are many different biologically active compounds found in fruits and vegetables. A lot of studies have measured fruit and vegetable intake with respect to cardiovascular disease or cancer. However, tthese studies cannot pinpoint an effect to a specific phytochemical.

Q: Is there evidence that fruits, vegetables, legumes, and whole grains help lower rates of certain cancers and heart disease?

A: Some evidence that these foods lower risk of cancer or heart disease comes from epidemiological studies, mainly prospective cohort studies, as well as a few randomized controlled trials.

Q: Does it matter whether plant foods are eaten raw or cooked?

A: Data regarding phytochemical content in raw versus cooked foods are limited. Cooking food causes changes in chemical composition that can affect the amount of nutrients and phytochemicals in food. The effect of cooking would depend on the specific phytochemical, food source, and cooking method, including length of cooking time. For example, water-soluble compounds may be leached into cooking water. Compared to boiling, cooking methods that use less water (such as microwaving or steaming) may better preserve water-soluble nutrients and phytochemicals.

Q: Is there a way to tell whether a food is rich in phytochemieals based on its color?

A: Yes. For instance, the carotenoid lycopene colors foods red. Other carotenoids, such as those found in carrots (i.e., beta-carotene), color foods orange. Some of the other carotenoids color foods yellow. Chlorophyll makes plants green, but chlorophyll in green vegetables can mask the color provided by other nutrients or phytochemicals, such as carotenoids. Anthocyanins give fruit a blue or purplish color.

Q: Are darker colors preferable to lighter colors?

A: Color is certainly an indicator of the phytochemicals in foods. I recommend eating a variety of different-colored fruits and vegetables.

Victoria J. Drake, Ph.D., is a Research Associate with the Linus Pauling Institute at Oregon State University in Corvallis, where she is also the Manager of the Micronutrient Information Center. More information is available online at
Colorful Foods and Their Phytochemicals

Color Group Vegetables Fruits

Blue/Purple Eggplants Blackberries
[ILLUSTRATIONS Purple cabbage Black currants
OMITTED] Purple peppers Blueberries
 Purple figs
 Purple grapes

Red Beets Cherries
[ILLUSTRATIONS Radicchio Cranberries
OMITTED] Radishes Pink grapefruit
 Red leaf lettuce Pomegranates
 Red peppers Raspberries
 Red potatoes Red apples
 Rhubarb Strawberries
 Tomatoes Watermelons
 Acorn squash Apricots

Orange/Yellow Butternut squash Cantaloupe
OMITTED] Pumpkin Mangoes
 Rutabagas Nectarines
 Summer squash Oranges
 Sweet corn Papayas
 Sweet potatoes Peaches
 yellow peppers Pineapples
 yellow potatoes Tangerines

Green Asparagus Avocados
[ILLUSTRATIONS Broccoli Green apples
OMITTED] Brussels sprouts Green grapes
 Cabbage Green pears
 Cucumbers Honeydew melons
 Green beans Kiwi fruit
 Green peas Limes
 Romaine lettuce

White Cauliflower Bananas
OMITTED] Endive Pears
 Garlic White nectarines
 Ginger White peaches
 White corn
 White potatoes

Color Group Phytochemicals Importance

Blue/Purple Anthocyanins Bolster cellular
[ILLUSTRATIONS Ellagic acids antioxidant
OMITTED] Epicatechin defenses. May
 Phenolic acids protect against
 Proantho- heart disease by
 cyanidins Preventing blood
 clots. Can help
 lower risk of some
 cancers. May aid in
 urinary tract
 health. May help to
 maintain optimal
 brain functioning.
 Protect against
 age-related memory
 loss, and delay the
 onset of
 Alzheimer's disease
 and other dementias.

Red Anthocyanins May protect against
[ILLUSTRATIONS Epicatechin heart and lung
OMITTED] Lycopene disease. May
 Phytoene promote memory
 Phytofluene function, heart
 Alpha-carotene health, and cancer
 prevention. Can
 help to maintain
 urinary tract
 health. May
 contribute to
 prostate health.

Orange/Yellow Alpha-carotene Protect against
[ILLUSTRATIONS Beta-carotene cancer by
OMITTED] Beta- bolstering cellular
 cryptothanxin anti-oxidant
 Bioflavonoids defenses. May
 Flavanones protect the skin
 Lutein against free
 Phenols radical damage and
 Zeaxanthin help to repair
 damaged DNA. May
 also promote cell
 communication. Can
 strengthen the
 body's immune
 system. May Provide
 support to heart
 and vision health.

Green Beta-carotene May enhance the
[ILLUSTRATIONS Glucosinolates detoxification of
OMITTED] Indoles undesirable
 Kothiocyanates compounds by
 Kaempferol bolstering cellular
 Lutein antioxidant
 Quercetin defenses and
 Sulforaphane neutralizing free
 Zeaxanthin radicals, which may
 damage cells. Can
 help ward off
 cancer by
 carcinogens. May
 May help to
 maintain strong
 bones and teeth.
 Can also promote
 vision health,
 including reducing
 the risk of
 cataracts and
 Preventing age-
 related macular

White Allicin May contribute to
[ILLUSTRATIONS Allyl sulfides maintaining our
OMITTED] Indoles body's healthy
 Kaempferol- immune functioning.
 Quercetin May help to
 control cholesterol
 levels from
 becoming elevated.
 May aid in keeping
 the heart healthy.
 May help to lower
 the risk of cancer.
 The onion family
 contains allicin,
 which has anti-
 tumor properties.
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Publication:Nutrition Health Review
Article Type:Interview
Geographic Code:1USA
Date:Sep 22, 2006
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