Functional Foods at a Glance: Evidence and Safety Table
One-page table of the foods in this library: what each is mostly studied for, the evidence label on its guide, and the main caution to know, with links to the full pages.
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.
This table is a map, not a menu. For each food it shows what the research has mostly looked at, the evidence label used on that food's own guide, and one caution worth knowing. It does not rank foods, recommend amounts or tell anyone what to eat for a health condition. A dietitian or clinician can say what suits a particular person.
How to read the table
- "Mostly studied for" names the outcome the sources we read looked at most, such as LDL cholesterol or blood pressure. It does not mean the food treats that condition.
- "Evidence label" is copied from the strength-of-evidence wording on the linked guide as of 2026-10-23, so the sources behind each label are listed on that guide. Where a guide gives different labels for different outcomes, we show the main ones. Open the guide before relying on a label. See the glossary for what each label means.
- Blood markers are not diseases. A drop in LDL cholesterol or blood pressure in a trial is not the same as fewer heart attacks or strokes.
- "Main caution" comes from a source we read for this page. "See the guide" means the guide has cautions we did not re-check here.
- Any food can cause an allergy: the FDA says more than 160 foods have been identified as causing food allergies in sensitive individuals. [1] For trouble breathing or swelling of the face or throat, call 911; see the food safety quick reference.
Fermented foods and drinks
| Food | Mostly studied for | Evidence label | Main caution |
|---|---|---|---|
| Yogurt | Lactose digestion; long-term health links in cohorts | Mostly observational; small randomized trials for cholesterol | The NHS lists unpasteurised yoghurt among foods to avoid in pregnancy. [2] |
| Kefir | Mouth bacteria, H. pylori treatment, cholesterol, blood pressure | Promising but limited (mouth bacteria, H. pylori); insufficient evidence (cholesterol, blood pressure) | NCCIH notes the risk of harmful effects from probiotics is greater in people with severe illnesses or compromised immune systems. [3] |
| Kimchi | Weight, blood sugar and cholesterol in small trials | Promising but limited | Check sodium on the label. The FDA says the Dietary Guidelines recommend adults limit sodium to less than 2,300 mg a day. [4] |
| Sauerkraut | Gut bacteria in one crossover trial | Biomarker only; no symptom or disease result in the sources read | Check sodium on the label (limit as stated above). [4] |
| Kombucha | Heart and metabolic markers | Insufficient evidence | One review says kombucha is contraindicated in infants, pregnant women, children under 4, and people with kidney failure or HIV. [5] |
| Miso | Japanese eating pattern; salt and cancer in one cohort | Promising but limited (pattern); evidence of association only (salt) | Check sodium on the label; it is also a soy food, and soy is a major U.S. allergen. [4][1] |
| Tempeh | Laboratory and animal work | Preclinical; no human trial for a health outcome | Soy is a major U.S. allergen. [1] |
| Natto | Vitamin K2 in blood; bone markers; deaths in cohorts | Promising but limited (blood K2, cohorts); insufficient evidence (bone) | Vitamin K foods and warfarin: the NHS says to talk to the warfarin clinic. [6] |
Fiber-rich foods
| Food | Mostly studied for | Evidence label | Main caution |
|---|---|---|---|
| Oats | LDL cholesterol | Established for the blood marker (trials); mixed for diabetes and heart disease (cohorts) | The NHS says oats can cause a reaction if produced in the same place as wheat, barley and rye. [7] |
| Barley | Cholesterol | Promising but limited (older trials) | Barley is one of the cereals containing gluten. [7] |
| Beans, lentils and chickpeas | LDL cholesterol; heart disease; blood sugar | Promising but limited (trials); mixed (heart disease, cohorts) | Raw or insufficiently cooked red kidney beans can cause acute toxicity. [8] |
| Flaxseed | Blood lipids, blood pressure | Promising but limited; insufficient evidence for weight loss | See the guide. |
| Chia seeds | Inflammation marker, blood pressure, cholesterol | Promising but limited; no good evidence of benefit for weight loss | See the guide. |
| Whole grains | Heart disease and diabetes in cohorts | Promising but limited (observational) | Some grains contain gluten. [7] |
Nuts, seeds and oils
| Food | Mostly studied for | Evidence label | Main caution |
|---|---|---|---|
| Walnuts | Cholesterol and blood fats | Promising but limited (markers) | Tree nuts are a major U.S. allergen. [1] |
| Almonds | Cholesterol, blood pressure, weight | Promising but limited; mixed for inflammation markers | Tree nuts are a major U.S. allergen. [1] |
| Pistachios | Blood sugar, insulin, blood pressure | Promising but limited | Tree nuts are a major U.S. allergen. [1] |
| Pumpkin seeds | Blood sugar after a meal; urinary symptoms | Promising but limited (few small trials) | See the guide. |
| Avocado | Cholesterol, blood sugar | Mixed (cholesterol); proper evidence not found for heart attacks and strokes | MedlinePlus says people on warfarin may need to limit vitamin K foods and keep the amount steady. [9] |
| Extra virgin olive oil | Heart events in a Mediterranean diet trial | Promising but limited; mixed for the oil alone | See the guide. |
Fruits and vegetables
| Food | Mostly studied for | Evidence label | Main caution |
|---|---|---|---|
| Blueberries | Blood vessel function | Promising but limited (a lab-style measure) | See the guide. |
| Pomegranate | Blood pressure, blood sugar | Promising but limited | A case report described a possible interaction between pomegranate juice and warfarin. [10] |
| Citrus fruits and orange juice | Heart disease and death in cohorts | Promising but limited (observational) | Grapefruit juice can block an intestinal enzyme and change how some medicines work. [11] |
| Tomatoes | Prostate cancer risk; blood fats and pressure | Mixed (prostate cancer); promising but limited (blood fats, pressure) | See the guide. |
| Broccoli and cruciferous vegetables | Cancer and heart risk in cohorts | Promising but limited (observational); insufficient evidence from trials | The NHS lists broccoli among foods high in vitamin K that can affect warfarin. [6] |
| Leafy greens | Heart disease in cohorts | Promising but limited | Same vitamin K and warfarin point. [6] |
| Beets and beet juice | Blood pressure | Promising but limited (low certainty) | See the guide. |
| Strawberries, raspberries and blackberries | Blood vessel function, blood sugar | Promising but limited; insufficient evidence for blackberries | See the guide. |
| Cranberries | Preventing urinary tract infections | Moderate certainty for prevention overall (Cochrane); no good evidence of benefit for treating an existing infection | The NHS says people on warfarin should not have cranberry juice or cranberry products. [6] |
| Tart cherries | Sleep, gout, exercise soreness | Promising but limited; mixed for gout | See the guide. |
| Onions, garlic and other alliums | Cancer risk in cohorts | Observational and mixed; insufficient evidence for colds | NCCIH warns that garlic supplements (not food) may increase bleeding risk. [12] |
Fish and soy
| Food | Mostly studied for | Evidence label | Main caution |
|---|---|---|---|
| Oily fish | Heart events and deaths in cohorts | Promising but limited (observational); insufficient evidence from trials of eating fish | The FDA publishes advice on choosing fish lower in mercury. [13] |
| Soy foods | LDL cholesterol | Established, small effect (trials of soy protein against other protein); mixed for heart events | Soy is a major U.S. allergen. [1] |
Drinks
| Food | Mostly studied for | Evidence label | Main caution |
|---|---|---|---|
| Black tea | LDL cholesterol, blood pressure | Promising but limited; mixed in short trials | Contains caffeine; the NHS says people who are pregnant should not have more than 200 mg a day. [2] See caffeine in foods and drinks. |
| Matcha and green tea as drinks | Blood pressure; deaths in cohorts | Promising but limited (elevated blood pressure); observational for deaths | NCCIH: liver injury has been reported with green tea products, mainly extracts in tablet or capsule form. [14] |
| Coffee | Many outcomes, mostly in cohorts | Observational association; mixed in trials | The NHS says people who are pregnant should not have more than 200 mg of caffeine a day. [2] |
| Dark chocolate and cocoa | Blood pressure, blood fats | Promising but limited (markers); mixed for cocoa extract, which is a supplement | Check the label for added sugars. [15] |
Spices as foods
| Food | Mostly studied for | Evidence label | Main caution |
|---|---|---|---|
| Turmeric as a spice | Research is on supplements, not the spice | Not assessable for the spice; promising but limited for some supplement uses | NCCIH: liver damage has been reported with highly bioavailable curcumin formulations. [16] |
| Ginger | Nausea in pregnancy, other uses | Promising but limited for some uses; not assessable for ginger as an everyday food | A systematic review lists ginger among foods and herbs clinicians should know about for bleeding risk with warfarin. [17] |
| Cinnamon | Blood sugar | Mixed; insufficient evidence for weight | NCCIH: some cassia products contain high levels of coumarin. [18] |
Cautions that apply across foods
- Medicines. Grapefruit, vitamin K foods and tyramine foods can matter with specific medicines. Ask the prescriber or pharmacist; see foods and medicine interactions and how interactions work.
- Raw sprouts. The FDA advises that people more vulnerable to foodborne illness avoid raw or lightly cooked sprouts of any kind. [19]
- Babies and young children. The NHS says whole nuts should not be given to children under 5 because they can choke, and honey should not be given before age 1. [20] See foods for babies and toddlers.
- Individual conditions. Kidney disease, pregnancy, diabetes medicines and others change what is suitable. See functional food safety.
Where to go next
A to Z directory, research by food for a longer evidence snapshot, and how to read nutrition research headlines.
Frequently asked questions
Does this table rank the best functional foods?
No. It shows what each food has mostly been studied for and how strong the evidence is on its own guide. There is no overall score and no "best" list.
Why do so many rows say "promising but limited"?
Most food research uses blood markers, small trials or observational studies. Observational studies monitor people in normal settings and do not test an intervention. [21] Open each guide to see the study types.
Is a food with an "established" label a treatment?
No. The label refers to a specific blood marker or outcome in studies, such as LDL cholesterol, not to treating a disease. Foods do not replace medicines; ask a clinician about your own situation.
Why is turmeric listed with a supplement caution?
Most turmeric research uses supplements, which carry liver-injury reports that NCCIH describes for highly bioavailable curcumin products. [16] The spice used in cooking is a different exposure.
Does a caution in the table mean I should avoid the food?
Not necessarily. It flags a group or situation to ask about, such as warfarin, pregnancy or an allergy. Check with a pharmacist or clinician, and never change a prescribed medicine on your own.
References
- U.S. Food and Drug Administration. Food Allergies.. Read 2026-10-23.
- NHS. Foods to avoid in pregnancy.. Read 2026-10-23.
- NCCIH. Probiotics: Usefulness and Safety.. Read 2026-10-23.
- U.S. Food and Drug Administration. Sodium in Your Diet.. Read 2026-10-23.
- Kombucha review (composition, benefits and regulation). J Food Sci 2022. PMID 35029317.. Read 2026-10-23.
- NHS. Warfarin.. Read 2026-10-23.
- NHS. Coeliac disease.. Read 2026-10-23.
- Severe red kidney beans toxicity in an 8-year-old girl: a rare case of hypovolemic shock and prerenal acute kidney injury. Int J Emerg Med 2026. PMID 41714947.. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia. Vitamin K.. Read 2026-10-23.
- Potential interaction between pomegranate juice and warfarin (case report). Emerg Med J 2010. PMID 20029019.. Read 2026-10-23.
- U.S. Food and Drug Administration. Grapefruit Juice and Some Drugs Don't Mix.. Read 2026-10-23.
- NCCIH. Garlic.. Read 2026-10-23.
- U.S. Food and Drug Administration. Advice About Eating Fish.. Read 2026-10-23.
- NCCIH. Green Tea.. Read 2026-10-23.
- U.S. Food and Drug Administration. Added Sugars on the Nutrition Facts Label.. Read 2026-10-23.
- NCCIH. Turmeric.. Read 2026-10-23.
- Warfarin and food, herbal or dietary supplement interactions: a systematic review. Br J Clin Pharmacol 2021. PMID 32478963.. Read 2026-10-23.
- NCCIH. Cinnamon.. Read 2026-10-23.
- U.S. Food and Drug Administration. Selecting and Serving Produce Safely.. Read 2026-10-23.
- NHS. Foods to avoid giving babies and young children.. Read 2026-10-23.
- National Institute on Aging. What Are Clinical Trials and Studies?. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.