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.