The general category of functional foods includes processed food or foods fortified with health-promoting additives, like "vitamin-enriched" products. Products considered functional generally do not include products where fortification has been done to meet government regulations and the change is not recorded on the label as a significant addition ("invisible fortification"). An example of this type of fortification would be the historic addition of iodine to table salt, or Vitamin D to milk, done to resolve public health problems such as rickets. Fermented foods with live cultures are considered functional foods with probiotic benefits.
Functional foods are part of the continuum of products that individuals may consume to increase their health and/or contribute to reducing their disease burden.
"Functional Food is a Natural or processed food that contains known biologically-active compounds which when in defined quantitative and qualitative amounts provides a clinically proven and documented health benefit, and thus, an important source in the prevention, management and treatment of chronic diseases of the modern age". It was debated at the 9th International Conference on "Functional Foods and Chronic Diseases: Science and Practice" at the University of Nevada, Las Vegas on March 15-17, 2011.Functional Food Center has adopted a new definition of functional food. 
Functional foods are an emerging field in food science due to their increasing popularity with health-conscious consumers and the ability of marketers to create new interest in existing products.
The functional food industry, consisting of food, beverage and supplement sectors, is one of the several areas of the food industry that is experiencing fast growth in recent years. It is estimated by BCC Research that the global market of functional food industry will reach 176.7 billion in 2013 with a compound annual growth rate (CAGR) of 7.4%. Specifically, the functional food sector will experience 6.9% CAGR, the supplement sector will rise by 3.8% and the functional beverage sector will be the fastest growing segment with 10.8% CAGR. This kind of growth is fueled not only by industrial innovation and development of new products that satisfy the demand of health conscious consumers but also by health claims covering a wide range of health issues. Yet, consumer skepticism persists mainly due to the fact that benefits associated with consuming the products may be difficult to be detected. The industry suggests the establishment of a health claim regulating agency, which may increase consumer confidence. Strict examination of some of the functional food claims may discourage some companies from launching their products.
Health claims 
Functional food products typically include health claims on their label touting their benefits: for example: "Cereal is a significant source of fiber. Studies have shown that an increased amount of fiber in one's diet can decrease the risk of certain types of cancer in individuals."
Some countries, such as Canada, Sweden, the United States and the European Union, have specific laws concerning the labeling of such products. In the United States, the kinds of claims which are allowed are overseen and regulated by the Food and Drug Administration (FDA). However, some claims will fall outside the range of the FDA and be accompanied by the disclaimer: "These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease."
Such a disclaimer typically accompanies supplements rather than foods, but since the definition of functional food is still evolving and somewhat amorphous, a functional food may find itself bearing the warning.
Current research 
The Richardson Centre for Functional Foods and Nutraceuticals, which is part of the University of Manitoba, is dedicated to the discussion, discovery, and development of functional foods and nutraceuticals, with a focus on the crops of the Canadian Prairies. Research involves candidates for functional food ingredients by examining the efficacy of novel bioactive materials such as plant sterols -- natural components found in plants which can act as cholesterol-lowering agents. Some researchers, however, have concerns that food supplements with plant sterol esters might increase cardiovascular risk, therefore calling for randomized controlled trials before such supplements can be recommended to the general public.
New Zealand Institute for Plant and Food Research also have a dedicated research team that works on functional foods. Their focus is on both 'whole-foods' and food extracts - examining extracts from berries and their effect on sports performance and recovery, as well as the gut-health and immune function role of natural fruits and vegetables. The group also work with 'mood foods' and the delivery mechanisms behind components in foods and beverages designed to enhance mental performance, brain function and cognitive ability.
The Functional Food Centre at Oxford Brookes University is the UK’s first research centre dedicated to functional food. The centre is known internationally for its work on Glycaemic Index and is the largest testing centre in Europe. The centre provides customer-focused research and consultancy services to the food and nutrition industry, UN and government agencies in the UK and overseas. The research and consultancy portfolio not only concentrate on the scientific characteristics of food and nutrition, but also integrate both the science and social aspects of food. The centre also focuses on areas such as satiety, dietary interventions, female nutrition and aging.
See also 
- Functional beverage
- Health claims on food labels
- Medical food, specially formulated foods to treat diseases with distinctive nutritional needs (e.g., an inability to metabolize a common molecule)
- Preventive medicine
- What are Functional Foods and Nutraceuticals? Agriculture and Agri-Food Canada
- Danik M. Martirosyan (Ed): Functional Foods and Chronic Diseases: Science and Practice. Food Science Publisher; 2011
- "FOSHU, Ministry of Health, Labor and Welfare, Japan". Unknown parameter
- Roberts, W. "Benefiting Beverages." Prepared Foods August 2009
- Scholan, I. "Functional Beverages-- where next? Innovation in functional beverages market is set to continue." International Food Ingredients December 2007.
- Functional Foods: Public Health Boon or 21st Century Quackery?, a review of regulations and demand for functional foods in Japan, the U.S. and the UK (March 1999)
- Functional food patents: beware potential pitfalls An article explaining some of the issues involved in obtaining patent protection for new functional foods.