What Are Functional Foods?
What functional foods are, how dietetic and FDA sources describe foods, supplements and fortified foods, what "superfood" does and does not mean, and how this library is organized.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read functional food safety before you use anything on this page.
A working definition
The American Dietetic Association (now the Academy of Nutrition and Dietetics) wrote a 2009 position paper. It says that "All foods are functional at some physiological level." [1] It then describes functional foods as including whole foods and fortified, enriched or enhanced foods that have a potentially beneficial effect on health when eaten as part of a varied diet on a regular basis, at effective levels. [1] The same paper says each functional food should be evaluated on the basis of scientific evidence. [1]We use the term for foods studied for health effects beyond basic nutrition. For each one we say whether the finding comes from a randomized trial, a population (cohort) study or a laboratory study. We also say which food was compared. "Instead of" and "in addition to" can give different answers.
What functional foods are not
| Term | What it means here |
|---|---|
| Dietary supplement | A product intended for ingestion that contains a "dietary ingredient" intended to supplement the diet, per the FDA. [2] It can come as capsules, gummies, liquids or powders. [2] Food results do not carry over to supplements, or the reverse. See Vitamins & Supplements. |
| Fortified food | A food with nutrients added. The FDA says its fortification policy discourages indiscriminate addition of nutrients to foods. [3] See Fortified Foods. |
| Superfood | A marketing word. A 2018 systematic review says no generally accepted definition exists. [4] See Superfoods: What the Word Means. |
| Probiotic | Live microorganisms that, given in adequate amounts, confer a health benefit on the host. [5] A fermented food is defined differently, as a food made through desired microbial growth and enzymatic conversions of food components. [6] Fermented does not automatically mean probiotic. |
| Medicine | On U.S. labels, the FDA says only a drug can legally claim to diagnose, treat, cure or prevent a disease. [7] See Functional Foods vs Supplements vs Medicine. |
How we judge a food
- Which kind of evidence? Randomized trials show what a food changed in a study. Population studies show an association, and people who eat a food often differ in other ways. A review of nutrition research lists measurement error and confounding among the main problems. [8]
- What was measured? Many food trials measure markers such as blood pressure or cholesterol, not heart attacks or strokes. A Cochrane review of Mediterranean-style diets, for example, found moderate-quality evidence of lower blood pressure in one comparison, while the studies in that comparison did not report clinical endpoints such as heart attack or stroke. [9]
- What exactly was eaten? Whole food, juice, powder and extract are different things. A trial of one does not transfer to another.
- Where evidence is missing, we write "Proper evidence not found" and say what we searched, rather than filling the gap.
Official eating guidance, for context
Official bodies describe whole patterns of eating more often than single foods. The WHO says a variety of minimally processed and unprocessed foods low in unhealthy fats, free sugars and sodium are the foundation of any healthy diet. [10] The NHS Eatwell Guide advises at least 5 portions of fruit and vegetables a day. [11] The U.S. Dietary Guidelines for Americans have been issued every five years since 1980. [12] See Dietary Patterns Studied.Where to go next
- Foods: A to Z directory and Functional Foods at a Glance.
- Fermented foods: Probiotics, prebiotics and fermented foods.
- Fiber-rich foods: Whole grains and ancient grains and Oats.
- Nuts, seeds and fats: Nuts and seeds for heart health.
- Fruits and vegetables: Fruit juice vs whole fruit.
- Fish, soy and protein: Oily fish and Soy foods.
- Drinks: Coffee and Black tea.
- Spices as food: Turmeric as a food.
- Nutrients and compounds: Nutrients and compounds in foods.
- Goals: By wellness goal.
- Everyday use: Preparation and everyday use and Food safety basics.
- Labels: Reading food labels.
- Safety: Functional food safety.
- Claims: Food claim checks.
- Science: Research and evidence and How to read nutrition research headlines.
- Side by side: Comparisons.
- Terms: Glossary of functional food terms.
Frequently asked questions
Are functional foods regulated as a category?
A single legal definition of "functional food" is not described in the sources we read. The FDA does describe claims that can appear on food labels: health claims, nutrient content claims and structure/function claims. [7] Which rules apply depends on the product and its label.
Is a superfood the same as a functional food?
No. "Superfood" is a marketing term. A 2018 systematic review of 113 human trials of foods described as superfoods found only limited evidence for effects on metabolic syndrome measures. [4]
Is a fermented food the same as a probiotic?
No. Probiotics are defined as live microorganisms with a shown benefit, [5] while fermented foods are defined by how they are made. [6] A fermented food may or may not contain live cultures. See Live Cultures on Labels.
Can a food replace a medicine?
Not as a substitute for care a clinician has prescribed. On U.S. labels, the FDA says only a drug can legally claim to diagnose, treat, cure or prevent a disease. [7] Ask the prescriber or pharmacist before changing any medicine.
Does food evidence prove cause and effect?
Not by itself. A meta-research study of nutrition found that on average, results from trials and cohort studies were similar, but differences in what was compared often explained the gaps. [16] Each guide says which kind of study it describes.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety comes first
- Food allergy. The FDA lists nine major allergens: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans and sesame. [13] For trouble breathing or swelling of the face or throat, call 911. See Food Allergy Basics and Emergency Signs.
- Medicines. Some foods change how medicines work. The FDA says some medicines carry warnings about grapefruit. [14] Ask a pharmacist or the prescriber. See How Interactions Work.
- Supplements are different. MedlinePlus notes that supplements do not have to go through the testing that drugs do. [15]
References
- American Dietetic Association. Position of the American Dietetic Association: functional foods. J Am Diet Assoc 2009. PMID 19338113. Read 2026-10-22 (abstract). The later Academy of Nutrition and Dietetics edition was not read.
- U.S. Food and Drug Administration. Questions and Answers on Dietary Supplements. Read 2026-10-22.
- U.S. Food and Drug Administration. Questions and Answers on FDA's Fortification Policy: Guidance for Industry. November 2015. Read 2026-10-22.
- Effects of superfoods on risk factors of metabolic syndrome: a systematic review of human intervention trials. Food Funct 2018. PMID 29557436. Read 2026-10-22 (abstract).
- Hill C et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol 2014. PMID 24912386. Read 2026-10-22 (abstract).
- Marco ML et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol 2021. PMID 33398112. Read 2026-10-22 (abstract).
- U.S. Food and Drug Administration. Label Claims for Conventional Foods and Dietary Supplements. Page dated 03/28/2024. Read 2026-10-22.
- Kamangar F, Karimi P. The state of nutritional epidemiology: why we are still unsure of what we should eat? Arch Iran Med 2013. PMID 23906255. Read 2026-10-22 (abstract).
- Rees K et al. Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev 2019. PMID 30864165. Read 2026-10-22 (abstract).
- World Health Organization. Healthy diet. Fact sheet. Read 2026-10-22.
- NHS (UK). Eating a balanced diet. Read 2026-10-22.
- U.S. Department of Agriculture and Department of Health and Human Services. Dietary Guidelines for Americans. Read 2026-10-22.
- U.S. Food and Drug Administration. Food Allergies. Read 2026-10-22.
- U.S. Food and Drug Administration. Grapefruit Juice and Some Drugs Don't Mix. Consumer Update. Read 2026-10-22.
- MedlinePlus. Dietary Supplements. U.S. National Library of Medicine. Read 2026-10-22.
- Schwingshackl L et al. Evaluating agreement between bodies of evidence from randomised controlled trials and cohort studies in nutrition research: meta-epidemiological study. BMJ 2021. PMID 34526355. Read 2026-10-22 (abstract).