Functional foods are generally considered foods or beverages that provide health benefits in addition to their basic nutrients. These foods may be whole foods (e.g., fruits, vegetables) or they may be enhanced to provide a benefit (e.g., orange juice fortified with calcium).

Common health benefits associated with functional foods include reductions in the risk of cancer, cardiovascular disease, diabetes and osteoporosis. Other possible benefits include a reduced risk of macular degeneration and gastrointestinal disorders, as well as improvements in memory.

The component of functional foods that provides a specific health benefit can come from plant sources (phytochemicals) or animal sources (sometimes referred to as zoochemicals). Fiber, soy protein, certain fatty acids and probiotics are examples of food components associated with specific health benefits.

Each component acts in a specific way in the body to impart a health benefit. Some may act as antioxidants, while some may trigger enzyme activity.

In general, a high-fiber, low-fat diet rich in plant foods (including 5 to 9 servings of fruits and vegetables per day) is recommended to promote good health and help reduce the risk of a variety of diseases and medical conditions.

Health claims may be made that identify a relationship between a specific food component and risk of disease. However, these claims are subject to approval by the U.S. Food and Drug Administration (FDA). Consumers should pay careful attention to packaging claims on foods. Claims made about developing component-disease relationships, or claims about how a component affects body function (structure-function claims), are less reliable than an FDA-approved health claim. Functional foods with FDA-approved health claims include oats and fortified margarine.

Functional foods are those products (foods or beverages) that provide added health benefits beyond their basic nutritional value. These health benefits may involve lowering the risk of certain diseases or conditions, or strengthening a person’s health in particular areas. Functional foods are also sometimes known as nutraceuticals, medicinal foods or designer foods.

Most, if not all, whole foods contain substances that appear to provide some type of health benefit beyond nutrition alone. For example, many different fruits and vegetables, nuts, oils, tea and wine include components that act as antioxidants (substances that neutralize cellular damage in the body), which may help reduce the risk of cancer.

In addition, whole foods may be altered or enhanced in order to provide specific health benefits. For example, low-fat foods can help reduce the risk of cardiovascular disease, and orange juice with added calcium may help strengthen bones.

Food is typically consumed for its taste and nutritional value. The types of nutrients provided by food are carbohydrates, fats, proteins, water, as well as certain vitamins and minerals. Nutrients are the chemical substances that help build, repair and maintain tissue growth throughout the body. Some nutrients are also transformed into energy in the body, which allows for the movement and proper functioning of various body processes. Other nutrients act as catalysts in the many reactions that occur in the body, including making energy.

To be considered functional, food must include a component associated with a specific health benefit in addition to its basic nutrients. Such components may naturally occur in the food, may be added to the food, or may be used to produce the food. They are sometimes referred to as bioactive food components because of their active effect on the body.

Some components come from animal sources and are sometimes referred to as zoochemicals. Many come from plant sources and are known as phytochemicals. There are thousands of phytochemicals, some of which may be associated with a variety of health benefits when consumed.

The bioactive food components in functional foods may perform different actions within the body, which can result in specific types of health benefits. These potential actions include:

• Antioxidant activity. Substances neutralize the cellular damage done by 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 substances act as antioxidants. This includes phytochemicals (e.g., carotenoids, flavonoids, resveratrol, ellagic acid), vitamins (e.g., vitamins A, C and E) and minerals (e.g., selenium).
  
  
• Hormonal action. Certain phytochemicals called phytoestrogens may mimic or alter the hormone estrogen in the body. This may provide consumers the possible benefits of estrogen (e.g., lowered cholesterol levels, strong bones, healthy heart, relief from hot flashes associated with menopause) while reducing the risk of reproductive cancers associated with estrogen (e.g., breast cancer, ovarian cancer). Phytochemicals that may act in this way include daidzein, genistein and lignans.
  

  

• 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. The class of phytochemicals known as isothiocyanates may perform this action.
  
  
• Interference with DNA replication. Certain substances can interfere with the replication of cells, which may inhibit growth of cancer cells. Phytochemicals such as saponins may act in this way.
  
  
• Antibacterial effect. Certain substances in functional foods can inhibit the growth of particular types of bacteria in the body. This includes probiotics (e.g., lactobacilli in certain yogurts that help manage levels of helpful and harmful bacteria in the digestive tract) and the phytochemical allicin (found in garlic).

In the United States, functional foods are an emerging trend not yet legally defined and facing limited regulation. In 1994, the National Academy of Science’s Food and Nutrition Board provided what has become the most commonly accepted definition of functional foods today -- foods that provide health benefits in addition to their basic nutrients.  

While oversight in the area of functional foods is still developing, the concept of functional foods is not new. In the 1920s, the mineral iodine was added to table salt in an effort to reduce the risk of goiter (an enlarged thyroid gland), which may occur due to a lack of iodine in the diet. Iodized salt is an early example of a food product enhanced to provide a specific health benefit beyond its nutritional value.  

Functional foods differ from health food, a generic term that is often used to refer to whole foods that are organically grown (produced without exposure to pesticides or chemical additives).

Functional foods differ from dietary supplements primarily in their intended use. Functional foods are conventional foods generally consumed for their taste as well as nutritional value. Dietary supplements are nutrients supplied in pill or liquid form that are intended to add to the food consumed as a part of a person’s diet.

Functional foods can be any type of food or beverage that provides health benefits in addition to its basic nutrients. Functional foods come in a variety of forms, including:

• Whole (conventional) foods. Foods that, in their natural state, provide certain health benefits when consumed. Examples include oats (provide soluble fiber that helps to lower cholesterol levels) and tomatoes (rich in lycopene, a phytochemical that appears to inhibit cancer cell growth). Many, if not all, whole foods contain substances that are associated with some type of health benefit and may be considered a functional food.
  
  
• Fortified foods. When nutrients or phytochemicals are added to foods to provide a specific health benefit. For example, orange juice fortified with calcium may help strengthen bones. Multigrain cereal may be enriched with flaxseed, which may reduce the risk of cancer. Certain types of fat substitutes contain a plant sterol (phytosterol) to help lower cholesterol. Many foods are now enhanced with a variety of vitamins and/or minerals (e.g., milk with vitamins A and D, flour with folic acid).
  
  
• Modified foods. Food that has been altered in such a way as to benefit a person’s health. For example, foods may be processed so that they include less fat than they originally contained. Low-fat or fat-free foods may help reduce the risk of cardiovascular disease. Additional foods are under development. For example, scientists are working on new types of flour the contain higher levels of antioxidants and soybeans with enhanced levels of calcium.

In some cases, an entirely new food may be created for the purpose of providing a specific health benefit. Examples include meat substitutes, such as products made with soy (e.g., soy burgers), as well as those made with mycoprotein (a protein derived from fungi). These meat substitutes can help lower cholesterol levels and may provide additional health benefits as well.

Food biotechnology (using living organisms to create food products) involves producing certain whole foods that contain specific amounts of a health-enhancing substance. This may include enhancing naturally occurring substances in food (e.g., producing a tomato that contains more lycopene than usual), or engineering foods to contain specific added ingredients (e.g., varieties of rice that include beta-carotene and iron).

Functional foods can offer a variety of health benefits. Common health benefits that may be associated with functional foods include reductions in the risk of certain cancers, cardiovascular disease, diabetes and osteoporosis. Other possible benefits include a reduced risk of macular degeneration and gastrointestinal disorders, as well as improvements in memory.

In most cases, health benefits associated with functional foods may be attributed to several different sources within the food, rather than one specific substance. For example, tomatoes include folate, vitamins C, A and E, as well as numerous phytochemicals (including high levels of lycopene). Due to a lack of scientific evidence it is unclear to what extent any one particular substance is responsible for a specific health benefit. It may be that one substance acts in conjunction with the others to produce the associated benefit.

Additional examples include oatmeal, which offers numerous health benefits due to its fiber, antioxidants, amino acids and phytosterol content. Legumes (e.g., peas, beans) contain fiber as well as several different phytochemicals (e.g., isoflavones, saponins, protease inhibitors) that can perform different actions associated with different health benefits.

The health-benefiting substances in functional foods are referred to as bioactive food components (BFC). They may come from plant sources (phytochemicals) or animal sources (sometimes referred to as zoochemicals). The bioactive food components of functional foods include:

• Phytochemicals (sometimes referred to as phytonutrients). Non-nutrient compounds found in plant foods. Some are associated with specific health benefits, beyond basic nutrition. There are a large variety of phytochemicals, available in an even larger variety of food sources. Several different types of phytochemicals may be present simultaneously in the same food source.
  
  
• Dietary fiber. The part of plant foods a human body cannot digest. Dietary fiber is considered a type of carbohydrate but not a nutrient because it is not absorbed into the body and does not provide calories. It may help regulate digestion (e.g., preventing constipation) and lower cholesterol levels. Soluble fiber may be more effective at reducing the risk of heart disease than insoluble fiber because it dissolves in water, and can help absorb cholesterol from food in the intestines. Fiber may also reduce the length of time the colon may be exposed to certain carcinogens, potentially lowering the risk of colon cancer. Fiber can be found in oatmeal, oat bran, rice, wheat bran, barley, beans (e.g., kidney, pinto beans) and many different fruits and vegetables.
  
  
• Soy protein. Soy may be associated with numerous health benefits. Most studied are its effects in helping to lower cholesterol levels, although recent reviews have called into question the level of cholesterol reduction. Soy is also associated with reducing the risk of heart disease, cancer, osteoporosis and possibly alleviating menopausal symptoms (e.g., hot flashes). Soy products can be produced with soy protein or the entire soybean (a type of legume). Both the protein and bean may contain certain phytochemicals (e.g., isoflavones, protease inhibitors, saponins). Soy protein can be used as a meat substitute to make plant-based burgers. Additional types of soy products include soy milk, tofu, miso, soybean oil, soy sauce and soy flour.
  
  
• Plant stanols and sterols. Plant molecules that mimic the structure of cholesterol. When consumed, they compete with animal-based cholesterol for absorption into the body. Plant stanols and sterols are not naturally present in plant foods in an amount significant enough to have this effect on the body. Thus, they are modified to form a chemical compound called esters. In this form, they may be incorporated into foods containing fat (e.g., margarine) or developed into fat substitutes without losing the cholesterol-lowering effects. In ester form and in appropriate quantities, these compounds may inhibit absorption of cholesterol from food in the small intestine. Small amounts of stanols and sterols are also found in fruits, vegetables, nuts, seeds, cereals, legumes and vegetable oils (especially soybean oil).
  
  
• Prebiotics and probiotics. Prebiotics involve nondigestible substances (e.g., fructo-oliogosaccharides contained in shallots) and probiotics involve live microorganisms (e.g., lactobacilli contained in certain yogurts and cultured dairy products). Both help to manage the levels of microorganisms within the digestive tract, increasing levels of helpful bacteria and reducing levels of harmful bacteria. A growing body of evidence suggests that probiotics and prebiotics may aid digestion, boost the immune system and protect against gastrointestinal problems.  Probiotics can have an anti-diarrheal effect, and prebiotics may aid in the absorption of certain minerals (e.g., calcium, magnesium). Prebiotics can also be found in whole grains, onions, bananas, garlic, honey, leeks and artichokes. When probiotics are combined with prebiotics, it is referred to as synbiotics.
  
  
• Fatty acids. Certain fatty acids are associated with specific health benefits. These include:
  
  
• Omega 3 fatty acids. A type of polyunsaturated fat commonly known as “omega-3,” which may lower the risk of cardiovascular disease. The three types of omega-3 fatty acids are  alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).  EPA and DHA can be found in fatty fish (e.g., salmon, sardines, tuna) and fish oils. ALA is found in walnuts and certain vegetable oils (e.g., flaxseed oil, canola oil).
  
  
• Conjugated linoleic acid (CLA). A type of fatty acid found in dairy products and some meats (e.g., beef, lamb) that is associated with a decrease in the risk of cancer.

National dietary guidelines have been historically based on the type of food and amount of nutrients needed for a body to properly function. Many functional foods (e.g., fresh fruits and vegetables, whole grains) are already part of current dietary guidelines. In addition, optimal levels of the bioactive food components in functional foods have not been established. 

Generally, a high-fiber, low-fat diet rich in plant foods (including 5 to 9 servings of fruits and vegetables per day) is recommended to promote good health and help reduce the risk of a variety of diseases and conditions (e.g., cancer, cardiovascular disease).

Common functional foods from plant sources include:

• Oats. An ideal source of soluble fiber that may lower cholesterol levels and reduce the risk of heart disease.
  
  
• Soy. Associated with lowering cholesterol levels (although this is now under debate) and reducing the risk of cardiovascular disease, cancer and when fortified with calcium, osteoporosis. There is speculation that soy may help alleviate menopausal symptoms.
  
  
• Flaxseed. A source of omega-3 fatty acids and the phytochemical lignan. It may be associated with lowering of cholesterol levels and anti-estrogen effects, such as reducing the risk of cancer.
  
  
• Tomatoes. A rich source of the phytochemical lycopene, which acts as an antioxidant and may be associated with reducing the risk of some types of cancer.
  
  
• Garlic. Contains the phytochemical allicin, which may stimulate certain enzymes in the body and have the effect of reducing the risk of cancer. It might also be associated with lowering blood pressure and levels of cholesterol, as well as helping to prevent bacterial and viral infections.
  
  
• Cruciferous vegetables. Vegetables from the cabbage family that naturally contain many different phytochemicals (e.g., indole, isothiocyanate) associated with potentially reducing the risk of certain cancers.
  
  
• Citrus fruits. These fruits contain a variety of healthy substances, including vitamin C, folate, fiber and various phytochemicals.
  
  
• Cranberry. This berry has been associated with a reduced risk of urinary tract infections. Flavonoids in cranberry likely prevent bacteria from attaching to the walls of the bladder. Cranberry juice also may help prevent stomach ulcers and gum disease. 
  
  
• Curry. A mixture of several spices that may help stop the growth of some cancer cells.
  
  
• Dark chocolate. Some research appears to indicate a decline in blood pressure after eating just under 4 ounces of dark chocolate a day. Phytochemicals such as flavonoids appear to be responsible for this effect. Milk chocolate does not appear to have the same effect, and it should be noted that most types of chocolate contain high levels of fat and calories.
  
  
• Tea. Both green and black teas may contain various types of phytochemicals (e.g., polyphenols, flavonoids) that are associated with a reduced risk of cancer. For centuries, members of the Hispanic community have used mate tea to treat disease.
  
  
• Wine, grapes. The skin of purple grapes contains the phytochemical resveratrol, which may help prevent heart disease and cancer. Fermented products that have spent significant time in contact with the skin of these grapes (e.g., red wine) also are a good source of resveratrol.  Moderate consumption (one or two 4-ounce glasses) of red wine also may help raise a person’s “good” HDL cholesterol while lowering “bad” LDL cholesterol. 

Common functional foods from animal sources include:

• Fish. Fatty fish, such as salmon and tuna, are good sources of omega-3 fatty acids, which may lower the risk of cardiovascular disease. The American Heart Association (AHA) recommends two servings per week of these types of fish.
  
  
• Dairy products. Dairy products are a good source of essential nutrients (e.g., calcium). Certain yogurts or other cultured products are also a good source of probiotics, which can help balance bacteria in the digestive tract and may help prevent gastrointestinal disorders. Consuming dairy products is associated with lowered risks of osteoporosis.
  
  
• Beef. Beef is a good source of conjugated linoleic acid (CLA), a fatty acid that may help prevent certain cancers.

Most functional foods provide their health benefits in regular serving size amounts. Simply eating a healthy, balanced diet may lessen the risk of many diseases or conditions, as well as promote good health. A balanced diet should include appropriate daily servings of whole grains, fruits, vegetables, meat, fish, poultry and dairy products.

Daily physical exercise and maintaining a healthy lifestyle are also important components to overall health. Functional foods can not offset poor health habits (e.g., smoking, lack of physical activity). Nor are they a cure for many diseases or conditions. Many health problems are affected by a variety of factors beside diet (e.g., genetics, stress, lifestyle choices). Thus, functional foods may be best suited for assistance in prevention or in mild cases of disease rather than as treatment.

Although dietary supplements exist for certain phytochemicals, obtaining these substances through foods is preferred. In some cases, supplements do not provide the same level of benefit as when it is consumed in food (e.g., lycopene, flavonoids). In other cases, the supplements have not been proven safe. For example, drinking green tea is generally considered safe but green tea supplements may actually be harmful. Also, beta-carotene in supplement form has been associated with an increased risk of lung cancer in smokers.

There is currently no legal definition for functional foods. The most commonly accepted definition for functional foods are those food or beverage products that provide health benefits in addition to their nutritional value.

Many different academic and regulatory organizations are working on how to scientifically support claims made for bioactive food components, those non-nutrient substances in functional foods that appear to provide a specific health benefit. In many cases, scientific evidence for the health claims are not conclusive.

The U.S. Food and Drug Administration (FDA) regulates functional foods according to their intended use and packaging claims. They do so under the authority of the Nutrition Labeling and Education Act (NLEA), which allows for disease or health-related messages on food labels. Food industry companies usually petition the FDA to consider new claims. In addition, any ingredients added to food products must be generally recognized as safe.

There are five types of claims allowed on food labels:

• Health claims. Confirmed statements about the relationship between food components and risk of disease. Claims are approved by the FDA based on significant scientific evidence. “Diets high in calcium may reduce the risk of osteoporosis” is an example of a health claim. The FDA has approved health claims for the following functional foods:
  
  
• • Oats (beta-glucan)
  • Certain fortified margarines (sterol/stanol esters)
  • Soy (soy protein)
    
    
• Qualified health claims. Statements about a developing relationship between a food component and risk of disease. Claims are approved by the FDA based on credible scientific evidence. Qualified health claims may include disclaimer language such as “There is scientific evidence supporting this claim, but it is not conclusive.” The FDA has approved a qualified health claim for tree nuts (monounsaturated fatty acids, vitamin E).
  
  
• Structure and function claims. Describes the effect of food components on body structure or function. These claims may not imply or state an association with a disease or medical condition. The exception is in the case of deficiency diseases (e.g., goiter, which may result from an iodine deficiency), which may be mentioned as long as its national prevalence is also mentioned.
  
  An example of a structure and function claim is “Calcium builds strong bones.” Structure and function claims can be made without prior FDA approval. A disclaimer must be included that states the FDA has not evaluated the claim and the product is not intended to diagnose, treat, cure or prevent any disease (because only medications may make that claim). A structure and function claim must be truthful and cannot be misleading.
  
  
• Dietary guidance claims. FDA-approved health claims that involve broad statements of health benefits for an entire food group. For example, “Diets rich in fruits and vegetables may reduce the risk of some types of cancer and other chronic diseases.”
  
  
• Nutrient content claims. Nutrient content claims involve comparative references to nutrient levels in a product (e.g., “low fat,” “reduced calorie”). These claims may be made in addition to a list of nutrients and nutrient levels that are required to be on the label of many foods. This list is typically contained in a bordered area and may include the amount of calories, fat, sodium, cholesterol, sugar and fiber contained in the product. 

Some people have criticized functional food claims as advertising gimmicks. They argue that, in many cases, specific health benefits are being used as a selling point to promote certain foods and beverages before there is adequate scientific research on the bioactive food component in question. In addition, many functional foods are simply whole foods like fruits and vegetables that are already included in the food guide pyramid.

Product advertising is regulated by the Federal Trade Commission (FTC). This is sometimes problematic because the FTC does not use the same standards regarding component-disease relationships as the FDA does in its food labeling regulations.

In general, consumers should pay close attention to the packaging claims of foods. Qualified health claims and structure and function claims are less reliable than unqualified, FDA-approved health claims.

Consumers should also be aware that products advertised as “fat-free” do not necessarily mean the item is healthy (e.g., it may contain sugar, which raises the calorie content). Also, calcium-fortified orange juice should not be considered a substitute for all the nutrients that can be gained from drinking milk. If in doubt, people are encouraged to consult their physician or dietitian about the safety and appropriateness of specific functional foods.

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 functional foods:

1. What types of functional foods may be especially beneficial for me?
   
   
2. How much of these types of foods should I consume?
   
   
3. Will I need to maintain a strict diet of these foods? If so, how do you recommend I do this?
   
   
4. Is there a dietitian or other professional you recommend I work with?
   
   
5. Can certain amounts of these foods be harmful to me?  Which ones should I be careful with?
   
   
6. Are there any other risks involved in consuming certain functional foods?
   
   
7. Do you recommend that I take certain dietary supplements instead of relying on functional foods? Why? Are there certain supplements I should avoid?
   
   
8. Will the functional foods I am consuming interfere with any of my current medications?
   
   
9. How can I find out which foods contain the substances my body needs?
   
   
10. What is the difference between functional foods and regular fruits and vegetables?