Phytochemicals are the non-nutrient substances found in plant food that are associated with certain health benefits.

Plants produce phytochemicals for their own protection (e.g., from pathogens, pests, environmental pollution) and for survival (e.g., to attract pollinators and seed dispersers). When humans consume plant foods, these phytochemicals are believed to provide protection for the human body as well.

Phytochemicals may act as antioxidants, affect hormone metabolism, stimulate enzyme activity and prevent potentially harmful DNA replication. These actions are associated with a variety of health benefits, including the potential to reduce the risk of some cancers.

There are thousands of phytochemicals, and many different ways to organize them. In common use, they are often referred to by their potential activity in the body (e.g., antioxidants, phytoestrogens).

Scientists typically categorize phytochemicals into classes based on similar chemical structures. Often, phytochemicals in the same class will have a similar effect on the body. Classes of phytochemicals include:

• Phenols. This includes flavonoids such as resveratrol, catechins, anthocyanins and isoflavones. Phenols also include phenolic acids and lignans.
  
  
• Terpenes. This includes carotenoids such as beta-carotene, lycopene and lutein. Terpenes also include monoterpenes and saponins.
  
  
• Thiols, also known as organosulfur compounds. This includes indoles and isothiocyanates.

Phytochemicals are found in a wide variety of plant foods, including most fruits and vegetables, as well as grains, legumes (peas and beans), nuts, seeds, and tea. Certain phytochemicals may also be available as supplements, although experts generally recommend people receive nutrients and other healthful substances from foods rather than supplements.

Phytochemicals refers to any chemical found in plants. This may include nutrients (e.g., vitamins, minerals) and non-nutrient substances (e.g., fiber, amino acids). However, in common usage, phytochemicals refer to a specific category of non-nutrient substances in plant foods.

Phytochemicals are substances that are not necessary for the human body to function. Thus, there are no recommended daily allowances or intake levels that exist for phytochemicals. Phytochemicals are considered a type of bioactive food component found in many whole foods. These substances appear to have potential associations with a wide variety of health benefits, ranging from inhibiting blood clots to reducing the risk of some cancers.

Phytochemicals are found in almost all fruits and vegetables, as well as in grains, legumes (peas and beans), nuts, seeds and tea. Different plants may contain a wide variety of phytochemicals, and in varying amounts. For example, an orange is estimated to contain more than 170 different phytochemicals.

Plants produce phytochemicals for protection and survival. Certain phytochemicals provide color, aroma and flavor to plants to help attract pollinators or other creatures that may help ensure survival of the plant (e.g., through dispersal of its seeds). Phytochemicals may also perform actions that protect a plant from damage due to pathogens (e.g., viruses, bacteria, fungi), pests (e.g., insects) and the environment (e.g., drought, sun). For example, many plants produce phytochemicals that act as antioxidants to protect against radiation damage caused by excess ultraviolet light from the sun. Other phytochemicals (e.g., allicin found in garlic) may be toxic to certain insects and microorganisms.

When edible portions of plants are consumed by humans, these phytochemicals appear to also provide protection to the human body. Many appear to promote human health by reducing the risk of various diseases such as cancer and cardiovascular disease.

There are thousands of different phytochemicals. Research on phytochemicals and their possible health benefits is ongoing, and new phytochemicals are still being discovered. Although certain phytochemicals are believed to be related to certain specific health benefits in the human body, there is no conclusive scientific evidence. Some experts believe phytochemicals work in conjunction with other substances in food (e.g., vitamins, minerals, other non-nutrient substances) to produce the associated benefit.

Most people obtain phytochemicals from consuming plant foods. Researchers are also investigating techniques that will allow them to produce foods that are bioengineered or fortified to contain higher levels of phytochemicals.

Certain phytochemicals may also be available as supplements (e.g., isoflavones, lutein, indoles). However, experts recommend people receive nutrients and other healthful substances from foods rather than supplements.

An individual plant food (e.g., a tomato) often contains vitamins and minerals as well as a variety of non-nutrient substances that offer health benefits (e.g., potassium, fiber), in addition to phytochemicals. Scientists also do not fully understand how phytochemicals work together to produce their presumed beneficial effects on the body. Therefore, it will be difficult to extract the proper phytochemicals for use in supplements until experts have a better grasp of how phytochemicals boost health.

There are thousands of different identified phytochemicals and many different ways to categorize them.

In common usage, phytochemicals are often characterized by their probable protective function in the human body. For example, many different phytochemicals act as antioxidants (preventing cellular damage in the body) and may be referred to simply as “antioxidants” rather than by their specific phytochemical name. Likewise, certain phytochemicals act as phytoestrogens (potentially affecting metabolism of the hormone estrogen in the body) and may be identified by this action.    

Scientists often organize phytochemicals into groups that share a similar chemical structure. Phytochemicals in the same class may often have similar effects on the body. Phytochemical classifications include:

• Phenols. A large class of phytochemicals, some of which are believed to have antioxidant properties and are associated with a lowered risk of heart disease and cancer. Phenols may be identified by a chemical structure that includes one or more hydroxyl groups (an oxygen atom bonded to a hydrogen atom) attached to an aromatic ring (six carbon atoms that form a hexagonal pattern). Certain phenols may impart a fragrance. When more than one hydroxyl group is involved, the phytochemical is known as a polyphenol. Phenols are sometimes also referred to as phenolic compounds. Examples of phytochemicals in this class include:
  
  

  Subclass:	Types of:
  Flavonoids	Flavonols (e.g., quercetin, resveratrol) Flavon-3-ols (e.g., catechins) Anthocyanins (e.g., cyanidin) Isoflavones (e.g., daidzein, genistein)
  Phenolic acids	Capsaicin Curcumin Ellagic acid Tannic acid (tannins) Vanillin
  Hydroxycinnamic acids	Caffeic acid Ferulic acid
  Lignans

Flavonoids such as resveratrol (found in red wine and grapes, peanuts) may help neutralize damage to the arteries caused by a high-fat diet. This type of phytochemical may inhibit cancer cell growth and heart disease by limiting blood clot formation and inflammation. Catechins (found in tea, wine) may help remove and prevent the development of carcinogens.

Isoflavones (e.g., daidzein, genistein) may act as a phytoestrogens, possibly reducing the risk of certain types of cancer. Sources of isoflavones include soybeans and soy products (e.g., soy flour, soy milk, tofu), apples, cherries, carrots, potatoes and garlic.

Different phenolic acids are associated with specific effects in the body. For example, capsaicin (found in hot peppers) may help regulate blood clotting. Ellagic acid (found in berries, red grapes, kiwi) may trigger enzyme activity that helps to rid the body of carcinogens.

Lignans can be found in flaxseed and whole grains, and are believed to inhibit the action of estrogen in the body, possibly reducing the risk of cancer.

• Terpenes. Another large class of phytochemicals believed to have antioxidant properties and associated with a lowered risk of heart disease and cancer. They may be identified as hydrocarbons (compounds consisting of carbon and hydrogen only) that come from isoprene (the major type of hydrocarbon emitted by plants). This class of phytochemicals includes:

Subclass:	Types of:
Carotenoids	Alpha-carotene Beta-carotene Lycopene Zeaxanthin Lutein
Monoterpenes	Limonene
Saponins

Beta-carotene (a provitamin A) can be found in fruits and vegetables that are yellow or orange in color (e.g., apricots, cantaloupes, papayas, carrots, sweet potatoes). It may also be found in dark green vegetables such as spinach and broccoli. Lycopene is found in tomatoes, watermelon, guava and papaya, as well as pink and red grapefruit.

Lutein is found in kiwi, egg yolks and green vegetables (e.g., spinach, romaine lettuce, broccoli) and is associated with a potential reduced risk for macular degeneration. Monoterpenes in the peels of citrus fruits are believed to trigger enzyme activity that may neutralize carcinogens in the body and inhibit cancer cell growth. Saponins are found in legumes (including soybeans and soy products), tomatoes, alfalfa sprouts and potatoes, and have been associated with enhancing immune system response and inhibiting cancer cell growth.

• Thiols. Also known as organosulfur compounds, phytochemicals in this class contain sulfur and may stimulate enzyme activity in the body, which may help prevent carcinogens from damaging DNA. They may emit a pungent smell. Some types (e.g., indoles) may also act as phytoestrogens. This class of phytochemicals includes:

Subclass:	Types of:
Indoles	Indole-3-carbinol
Isothiocyanates	Sulforaphane
Allyl sulfides	Allicin

Indoles and isothiocyanates are found in cruciferous vegetables (broccoli, Brussels sprouts, cabbage, cauliflower, horseradish, mustard and collared greens, turnips and kale). Allicin is not present in garlic in its natural state, although this phytochemical becomes available after garlic has been crushed or chopped. 

Additional classes of phytochemicals include:

• Phytosterols. Structurally similar to animal cholesterol, phytosterols may compete with cholesterol from animal-based foods for absorption into the body, helping to decrease cholesterol levels. This may help protect against heart disease. Sources of phytosterols include soybeans and certain fat substitutes.
  
  
• Phytic acids.  Also known as inositol hexaphosphate or phytate, these phytochemicals bind to minerals and may prevent the development of free radicals, which may reduce the risk of cancer. Sources of phytic acids include whole grains, nuts, oats, whole soybeans, and seeds.
  
  
• Protease inhibitors. These phytochemicals may inhibit enzyme production in cancer cells, which may slow tumor growth and/or prevent malignant changes. Sources of protease inhibitors include Brussels sprouts, potatoes, soybeans and soy products.

The health benefits of phytochemicals have not been conclusively proven. Scientific research in the area is ongoing. Potential health benefits are difficult to substantiate because it is unclear whether desired effects are the result of a single phytochemical, group of phytochemicals, or phytochemicals working with other nutrients or non-nutrient substances present in food.  

Despite a lack of conclusive scientific evidence, different phytochemicals have been associated with helping to prevent or treat diseases such as cancer, cardiovascular disease, diabetes and hypertension. Phytochemicals appear to have various beneficial effects in the human body, including:

• Antioxidant activity. Certain phytochemicals may stop the cellular damage of free radicals, the toxic chemical compound produced when oxygen is metabolized by the body. This slows the wear of body cells and may lower the risk of heart disease and inhibit growth of cancer cells. Many different phytochemicals act as antioxidants, including carotenoids, flavonoids and phenolic acids (e.g., ellagic acid, tannins). Recent research has linked consumption of the phytochemicals in some fruits and vegetables to reduced risk of certain types of cancer.
  
  
• Effect on hormone metabolism. Some phytochemicals can mimic or alter the hormone estrogen in the body. Phytochemicals that act in this way are also referred to as phytoestrogens. These actions may provide estrogen-related benefits (e.g., lowered cholesterol levels, strong bones, healthy heart, relief from hot flashes associated with menopause). It may also provide anti-estrogen benefits, such as a reduced risk of reproductive cancers (e.g., breast cancer, ovarian cancer). Phytoestrogens may also enhance communication among body cells. Phytochemicals with these possible actions include certain isoflavones (e.g., daidzein, genistein) lignans and indoles.
  

  

• Stimulation of enzymes. Certain phytochemicals can trigger enzymes to act in such a way that reduces the risk of disease (e.g., cancer). Stimulated enzymes may neutralize and/or remove carcinogens from the body. Phytochemicals that may perform this type of activity include phenolic acids (e.g., curcumin, ellagic acid), organosulfur compounds (e.g., isothiocyanates) and protease inhibitors.
  
  
• Prevention of potentially harmful DNA replication. Some phytochemicals can interfere with the replication of cells, which may inhibit growth of cancer cells. Phytochemicals such as monoterpenes, resveratrol and saponins may act in this way.
  
  
• Antibacterial effects. The phytochemical allicin (found in garlic) may inhibit the growth of particular types of bacteria in the body. 

Phytochemicals obtained by eating a healthy, balanced diet are generally believed to be safe. Phytochemicals may be found in almost all fruits and vegetables, as well as grains, legumes (peas and beans), nuts, seeds and tea.

There is no reliable scientific evidence that taking phytochemicals in supplement form is as beneficial as consuming foods that contain phytochemicals. It is also unknown what amount of a phytochemical supplement would be needed to produce the desired effects.

Phytochemical supplements may have possible interactions with some medications.  Therefore, it is recommended to talk to your doctor before taking phytochemical supplements.

It is unclear what, if any, potential risks may be associated with phytochemicals. Research is ongoing regarding the specific actions phytochemicals perform in the human body. The beneficial or adverse effects of phytochemicals have not been conclusively determined.

Preparing questions in advance can help patients have more meaningful discussions with health professionals regarding their conditions. Patients may wish to ask their doctor or registered dietitian the following questions related to phytochemicals:

1. Are there phytochemicals that may be especially beneficial for me?
   
   
2. What foods should I consume to obtain these phytochemicals?
   
   
3. How much should I consume daily or weekly?
   
   
4. Should I keep track of my consumption? How do you recommend I do this?
   
   
5. Do you recommend I take a phytochemical supplement?
   
   
6. For how long should I increase my intake of a particular phytochemical or take a supplement?
   
   
7. Will certain phytochemicals or supplements interfere with any condition I have or medications I am currently taking?
   
   
8. Can I get too much of a particular phytochemical or supplement?
   
   
9. What are the symptoms of overdose?
   
   
10. What changes in my condition should I report to you?