Frequently Asked Questions About Phytonutrients

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Frequently Asked Questions About Phytonutrients

JoAnn Guest

Apr 23, 2006 17:18 PDT

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Frequently Asked Questions About Phytonutrients

 

WebMD Public Information from the United States Department of

Agriculture

 

http://www.webmd.com/content/article/105/107783.htm

 

What are phytonutrients and where are they found?

What are the major classes of phytonutrients?

How do phytonutrients protect against diseases?

What is the evidence that fruit and vegetable consumption protects

human

health?

Are Americans eating enough fruits and vegetables?

What is the present state of phytonutrient research?

1. What are phytonutrients and where are they found?

 

The term " phyto " originated from a Greek word meaning plant.

Phytonutrients are certain organic components of plants, and these

components are thought to promote human health. Fruits, vegetables,

grains, legumes, nuts, and teas are rich sources of phytonutrients.

Unlike the traditional nutrients (protein, fat, vitamins, minerals),

phytonutrients are not " essential " for life, so some people prefer

the

term " phytochemical. "

 

 

 

2. What are the major classes of phytonutrients?

 

Some of the common classes of phytonutrients include:

 

 

Carotenoids

 

Flavonoids (Polyphenols), including Isoflavones (Phytoestrogens)

 

Inositol Phosphates (Phytates)

 

Lignans (Phytoestrogens)

 

Isothiocyanates and Indoles

 

Phenols and Cyclic Compounds

 

Saponins

 

Sulfides and Thiols

 

Terpenes

 

About Carotenoids

 

Of all the phytonutrients, we probably know the most about

carotenoids,

the red, orange, and yellow pigments in fruits and vegetables. The

carotenoids most commonly found in vegetables (and in plasma) are

listed

below along with common sources of these compounds. Fruits and

vegetables that are high in carotenoids appear to protect humans

against

certain cancers, heart disease, and age-related macular degeneration.

 

Carotenoid Common Food Source

alpha-carotene carrots

beta-carotene leafy green and yellow vegetables (eg. broccoli, sweet

potato, pumpkin, carrots)

beta-cryptoxanthin citrus, peaches, apricots

lutein leafy greens such as kale, spinach, turnip greens

lycopene tomato products, pink grapefruit, watermelon, guava

zeaxanthin green vegetables, eggs, citrus

 

For a more detailed discussion of carotenoid content of fruits and

vegetables see Chug-Ahuja et al, Journal of the American Dietetic

Association, 1993; vol 93: pp 318 and Mangels et al. Journal of the

American Dietetic Association, 1993; vol 93: pp 284-296. For

carotenoid

values of specific foods see the USDA-NCC Carotenoid Database for

U.S.

Foods on the web site of the Nutrient Database Laboratory.

 

About Polyphenols

Polyphenolic compounds are natural components of a wide variety of

plants; they are also known as secondary plant metabolites. Food

sources

rich in polyphenols include onion, apple, tea, red wine, red grapes,

grape juice, strawberries, raspberries, blueberries, cranberries,

and

certain nuts. The average polyphenol/ flavonoid intake in the U.S.

has

not been determined with precision, in large part, because there is

presently no U.S. national food database for these compounds (USDA

scientists and their colleagues are in the process of developing a

database for foods rich in polyphenols). It has been estimated that

in

the Dutch diet a subset of flavonoids (flavonols and flavones)

provide

23 milligrams per day. Earlier estimates of dietary intake that

approximated 650 milligrams per day (Kuhnau, World Review of

Nutrition

and Dietetics, 1976; vol 24: pp 117) are generally thought to be too

high as the estimate was based on data that were generated by " old "

(less specific) methodology. Scientists at the Food Composition

Laboratory, Beltsville Human Nutrition Research Center are currently

developing new methodology for the accurate measurement of

polyphenols

in foods.

 

Polyphenols can be classified as nonflavonoids and flavonoids. The

flavonoids quercetin and catechins are the most extensively studied

polyphenols relative to absorption and metabolism.

 

Nonflavonoids Sources

ellagic acid strawberries, blueberries, raspberries

coumarins

Flavonoids Sources

anthocyanins Fruits

catechins tea, wine

flavanones citrus

flavones Fruits and vegetables

flavonols Fruits, vegetables, tea, wine

isoflavones soybeans

 

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3. How do phytonutrients protect against disease?

 

The following are commonly proposed mechanisms by which

phytonutrients

may protect human health. More research is needed to firmly

establish

the mechanisms of action of the various phytochemicals.

 

Phytonutrients may:

 

Serve as antioxidants

Enhance immune response

Enhance cell-to-cell communication

Alter estrogen metabolism

Convert to vitamin A (beta-carotene is metabolized to vitamin A)

Cause cancer cells to die (apoptosis)

Repair DNA damage caused by smoking and other toxic exposures

Detoxify carcinogens through the activation of the cytocrome P450

and

phase II enzyme systems

 

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4. What is the evidence that fruit and vegetable consumption

protects

human health?

 

Evidence that fruit and vegetable consumption protects human health

is

accumulating from large population (epidemiological) studies, human

feeding studies, and cell culture studies. Listed below are a few

selected population studies from the literature linking fruit and

vegetable consumption to health. For an excellent review concerning

vegetables, fruit, and cancer prevention, see Steinmetz and Potter,

Journal of the American Dietetic Association 1996; vol 96: pp 1027.

 

Evidence That Carotenoids Are Protective

Fruit and vegetable consumption has been linked to decreased risk of

stroke -- both hemorrhagic and ischemic stroke. Each increment of

three

daily servings of fruits and vegetables equated to a 22% decrease in

risk of stroke, including transient ischemic attack (Gillman et al.

Journal of the American Medical Association. 1995; vol 273; pp 1113).

 

Elderly men whose intake of dark green and deep yellow vegetables

put

them in the highest quartile for consumption of these vegetables had

about a 46% decrease in risk for heart disease relative to men who

ranked in the lowest quartile. Men in the highest quintile had about

a

70% lower risk of cancer than did their counterparts in the lowest

quintile. The differences in vegetable consumption between high and

low

intake rankings were not striking. Men in the highest quartile or

quintile consumed more than two (>2.05 and >2.2) servings of dark

green

or deep yellow vegetables a day; those in the lowest quartile or

quintile consumed less than one serving daily (<0.8 and <0.7). This

suggests that small, consistent changes in vegetable consumption can

make important changes in health outcomes (Gaziano et al. Annals of

Epidemiology 1995; vol 5: pp 255 and Colditz et al. American Journal

of

Clinical Nutrition 1985; vol 41: pp 32).

 

Consumption of tomato products has been linked to decreased risk of

prostate cancer. Men in the highest quintile for consumption of

tomato

products (10 or more servings a week) had about a 35% decrease in

risk

of prostate cancer compared with counterparts whose consumption put

them

in the lowest quintile (1.5 or fewer servings of tomato products a

week)

(Giovannucci et al. Journal of the National Cancer Institute 1995;

vol

87: pp 1767).

 

People in the highest quintile for consumption of spinach or collard

greens, plants high in the carotenoid lutein, had a 46% decrease in

risk

of age-related macular degeneration compared with those in the

lowest

quintile who consumed these vegetables less than once per month

(Seddon

et al. Journal of the American Medical Association. 1994; vol 272:

pp

1413).

 

Evidence That Polyphenols Are Protective

Flavonoid consumption has been linked to lower risk of heart disease

in

some, but not all, studies. Elderly Dutch men in the highest tertile

of

flavonoid intake had a risk of heart disease that was about 58%

lower

than that of counterparts in the lowest tertile of intake. Those in

the

lowest tertile consumed 19 milligrams or less of flavonoids per day,

whereas those in the highest tertile consumed approximately 30

milligrams per day or more (Hertog et al. Lancet. 1993; vol 342: pp

1007). Similarly, Finnish subjects with the highest quartile of

flavonoid intake had a risk of mortality from heart disease that was

about 27% (for women) and 33% (form men) lower than that of those in

the

lowest quartile (Knekt et al. British Medical Journal. 1996; vol

312: pp

478).

 

However, in other studies the protective effect of flavonoids could

not

be confirmed. For Welch men, flavonol intake did not predict a lower

rate of ischemic heart disease and was weakly positively associated

with

ischemic heart disease mortality (Hertog et al. American Journal of

Clinical Nutrition. 1997; vol 65: pp 1489). For U.S. male health

professionals, data did not support a strong link between intake of

flavonoids and coronary heart disease (Rimm et al. Annals of

Internal

Medicine. 1996; vol 125: pp 384).

 

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5. Are Americans eating enough fruits and vegetables?

 

An excellent source of information on fruit, vegetable and grain

intake

of Americans is USDA's 1994/96 Continuing Survey of Food Intakes by

Individuals conducted by the Food Surveys Research Group, Beltsville

Human Nutrition Research Center. The following information comes

from

that survey.

 

About Vegetable Intake

On average, Americans consume 3.3 servings of vegetables a day.

However,

dark green vegetables and deep yellow vegetables each represent only

0.2

daily servings.

 

On any given day, about 49% of the population consumes at least the

minimum number of servings of vegetables recommended (3 servings per

day); 41% consume the number of servings recommended based on

caloric

intake (3 servings per day for those consuming less than 2200

calories,

4 servings per day for those consuming 2200-2800 calories, 5

servings

per day for those consuming 2800 calories or more). About 10% of the

population consumes less than one serving of vegetable per day.

 

About Fruit Intake

On any given day about 29% of the population consumes at least the

minimum number of servings of fruit recommended (two servings per

day);

24% consume the number of servings recommended based on caloric

intake

(two servings per day for those consuming less than 2,200 calories,

three for those consuming 2,800 calories, four for those consuming

2,800

calories or more). About 48% consume less than one serving of fruit

a

day.

 

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6. What is the present status of the art of phytonutrients research?

Population studies have linked fruit and vegetable consumption with

lowering the risk for chronic diseases including specific cancers

and

heart disease. However, media and consumer interest in

phytonutrients

and functional foods is far ahead of established proof that

documents

the health benefits of these foods or food components for humans.

Phytonutrients research is experiencing remarkable growth.

Hopefully,

more specific information on phytonutrient consumption and human

health

will be forthcoming in the near future. For now, it appears that an

effective strategy for reducing risk of cancer and heart disease is

to

increase consumption of phytonutrient-rich foods including fruits,

vegetables, grains and teas.

 

Reviewed by Charlotte E. Grayson, MD, April 2005.

 

SOURCE: USDA, Beltsville Human Nutrition Research Center,

Beltsville,

Md.

 

 

 

JoAnn Guest

mrsjo-

www.geocities.com/mrsjoguest/Diets