Agar (Agar-Agar): Nutrients, What Research Shows and Safety
Agar (agar-agar) from red seaweed: a vegetarian gelling agent. USDA values, what the EU safety review found, the dry-swallowing and bowel-blockage caution, and why diet claims lack trials.
Content last updated . This page has not been medically reviewed.
Agar, also sold as agar-agar or kanten, is a gel-forming extract of red seaweeds such as Gelidium and Gracilaria. It is sold as a powder, flakes or bars and is used to set jellies, desserts and vegetarian "gelatin" dishes. It is also a food additive with the E number E 406. [3] This page keeps agar as a cooking ingredient apart from fiber supplements and from diet hype, and says plainly where we found no good human evidence.
Read this first
- Do not swallow dry agar powder or flakes. Agar swells in water. We found one published case report of an agar-agar bezoar (a lump of undigested material) in the stomach pouch of a person who had gastric bypass surgery. [4] Dissolve agar by heating it in liquid, as recipes direct, and eat it as a set gel. If you have trouble swallowing, a narrowed bowel, or past bowel surgery, ask a clinician first.
- Safety as a food additive: the EU's food safety agency (EFSA) re-evaluated agar in 2016 and saw no safety concern for the general population at the uses reported. It said no numerical acceptable daily intake was needed. [3]
- No proof for diet claims. We did not find a trial in the sources we read showing that agar helps with constipation, weight loss or blood sugar. "Proper evidence not found in the sources we read."
- Iodine and metals: we did not find an agar-specific iodine or metal figure in the sources we read. Seaweeds as a group can carry iodine and metals. [6] If you have thyroid disease, ask your clinician about seaweed products in general. [8]
What is in it (USDA values)
USDA FoodData Central has two agar entries: "Seaweed, agar, dried" (item 170090) [1] and "Seaweed, agar, raw" (item 169280) [2]. They are different forms and must not be mixed. The raw entry has a USDA household portion of 2 tablespoons (about 10 g). The dried entry has none. Dried agar is almost always used in very small amounts, so the "per 100 g" figures for dried agar describe the concentrated dry weight, not what a serving gives.
| Nutrient | Dried, per 100 g [1] | % Daily Value | Raw, per 100 g [2] | Raw, per 2 tbsp (about 10 g) [2] |
|---|---|---|---|---|
| Energy | 306 kcal | not set | 26 kcal | 2.6 kcal |
| Water | 8.68 g | not set | 91.32 g | 9.1 g |
| Carbohydrate | 80.88 g | 29% | 6.75 g | 0.68 g |
| Fiber | 7.7 g | 28% | 0.5 g | 0.05 g |
| Protein | 6.21 g | 12% | 0.54 g | 0.05 g |
| Calcium | 625 mg | 48% | 54 mg | 5.4 mg |
| Iron | 21.4 mg | 119% | 1.86 mg | 0.19 mg |
| Magnesium | 770 mg | 183% | 67 mg | 6.7 mg |
| Manganese | 4.3 mg | 187% | 0.373 mg | 0.04 mg |
| Folate (DFE) | 580 mcg | 145% | 85 mcg | 8.5 mcg |
| Vitamin K | 24.4 mcg | 20% | 2.3 mcg | 0.23 mcg |
| Sodium | 102 mg | 4% | 9 mg | 0.9 mg |
% Daily Value uses the FDA 2016 Daily Values and is for 100 g of dried agar. Values vary with species, harvest and processing. USDA lists vitamin B-12 as 0 and no iodine; that does not tell us anything about whether agar has or lacks those, so see our B12 claims guide. [1] The raw portion gives well under 10% of any Daily Value, so agar is not a practical source of these nutrients.
The main component is a gel-forming carbohydrate, not a vitamin or mineral. EFSA describes agar as largely not absorbed and only slightly fermented by gut bacteria. [3]
What research says
| Health goal | What the sources found | Strength of evidence | What was studied |
|---|---|---|---|
| Safety as a food additive (E 406) | EFSA found no genotoxicity concern and no cancer effect in mice or rats at the highest doses tested. Humans tolerated 64 mg per kg of body weight a day for 12 weeks without noticeable side effects. EFSA saw no safety concern for the general population. [3] | Established for tolerability at the uses reviewed | Rodent studies; one human study for tolerance; food-category exposure estimates |
| Constipation or bowel regularity | We did not find a modern human trial in the sources we read. | Insufficient evidence | Not applicable |
| Weight loss or blood sugar | We did not find a human trial of agar for weight or blood sugar. A systematic review of whole brown seaweeds (not agar, which is from red seaweed) found lower blood glucose but no high-quality trial. [10] | Insufficient evidence for agar | Not applicable |
| Blockage if swallowed dry | One case report of an agar bezoar after gastric bypass. [4] | Case report only | One patient |
| Safety of seaweed polysaccharides | A 2025 review of agar, carrageenan and alginate food safety calls for better digestion models and notes that carrageenan's safety is still debated. [5] | Mixed (review of the field) | Laboratory and animal studies, reviews |
Eaten as food vs taken as a supplement. All the safety work above is for agar as a food ingredient. We did not find a trial of agar capsules or "agar diet pills" in the sources we read, so we say nothing in favor of them.
How much is a normal serving
There is no official serving size for dried agar. The USDA household portion for raw agar is 2 tablespoons (about 10 g), which has about 2.6 kcal. [2] That is information from the data, not a prescription. We did not read a source giving a standard cooking amount of dried powder, so check the recipe or package. The EFSA human tolerance figure of 64 mg per kg of body weight a day for 12 weeks is a research result, not advice. [3]
Safety, allergy and medicines
- Swallowing and blockage: agar swells in liquid. A case report describes an agar-agar bezoar causing food intolerance in a gastric bypass pouch. [4] We did not read a systematic review of agar blockage, so we cannot say how common it is. Always dissolve agar fully in hot liquid as recipes direct.
- Infants and young children: we did not read a child-specific limit for agar. EFSA's refined exposure for toddlers reached up to 26 mg per kg of body weight a day at the 95th percentile and it saw no concern. [3]
- Iodine and thyroid: seaweed iodine varies hugely, and kombu-type kelps can supply large amounts. [6] [7] We found no iodine value for agar in the sources we read, so we cannot say agar is low or high. The NHS says long-term high iodine intake may change thyroid function. [8] Ask your clinician if you have thyroid disease. See iodine in seaweed.
- Metals: EFSA's 2023 exposure work covered seaweeds and halophytes in general, not agar specifically. [6]
- Medicines: we did not read a source describing an agar-medicine interaction. As with other gel-forming fibers, ask a pharmacist about timing if you take several medicines. [9]
- Allergy: we did not find agar allergy reports in the sources we read. Seaweed is not shellfish or fish. For trouble breathing or swelling of the face or throat after any food, call 911 (or your local emergency number).
- Pregnancy and breastfeeding: we did not read an official statement about agar. See seaweed in pregnancy.
Choosing, storing and food safety
- Agar is sold as powder, flakes or bars, and the label should list agar or agar-agar as the only ingredient. Plain agar is used in vegetarian and vegan cooking in place of animal gelatin; see the label notes on vegan labels.
- We did not read a source with agar storage times, so follow the package.
Related pages
Health connections for Agar (Agar-Agar)
What research links to eating or drinking this food, and how strong the evidence is. Many studies are observational or use juice, powder, oil or extracts rather than the food as eaten; each card says which.
Agar (E 406) as a food additive: EFSA safety view
Clinically supportedEFSA saw no safety concern for the general population at reported uses and needed no numerical limit. Humans tolerated a research dose for 12 weeks.
Supplements: This is a safety conclusion for food use, not a health benefit.
Agar and constipation or bowel regularity
Not enough evidenceWe did not find a modern human trial of agar for constipation in the sources we read. Agar is largely not absorbed and is only slightly fermented.
Supplements: No evidence of benefit from supplements found.
Agar and weight loss or blood sugar
Not enough evidenceNo human trial of agar for weight or blood sugar was found. A review of whole brown seaweeds is a different food and found no high-quality trial.
Supplements: Not shown for agar.
Agar as a source of minerals
Not enough evidenceDried agar has large mineral values per 100 g in USDA data, but a realistic amount of agar adds very little.
Supplements: The raw 2 tablespoon portion gives well under 10 percent of any Daily Value.
Agar and gut bacteria
Lab or animal research onlyEFSA describes agar as slightly fermented by gut microbiota. No health outcome was shown from this.
Supplements: No supplement benefit shown.
Agar and iodine or metals in seaweed products
Not enough evidenceSeaweeds in general can carry iodine and metals. We found no agar-specific figure in the sources we read.
Supplements: Not applicable.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Body systems (1)
- Digestive SystemDocumented risk
Agar swells in liquid. One case report links agar to a blocked stomach pouch after gastric bypass, so it should be dissolved, not swallowed dry.
Body parts (1)
- StomachDocumented risk
A case report describes an agar-agar bezoar in the stomach pouch after gastric bypass surgery. One case, so how common this is remains unknown.
Documented risks and interactions (1)
- Agar and choking or stomach blockage if swallowed dry. A case report describes an agar-agar bezoar blocking a stomach pouch after gastric bypass. Agar swells in liquid, so it should be dissolved by heating, not swallowed dry.
Frequently asked questions
Is agar the same as gelatin?
No. Agar comes from red seaweed and is plant based. Gelatin comes from animal collagen. Agar is used as a vegetarian substitute in cooking. [3]
Is agar safe to eat?
EFSA's 2016 review saw no safety concern for the general population at the uses reported, and no numerical limit was needed. [3] Dissolve it in liquid rather than swallowing it dry. [4]
Does agar help with constipation or weight loss?
We did not find a human trial in the sources we read that shows it does. Claims online are mostly traditional use or lab ideas. "Proper evidence not found in the sources we read."
Does agar contain iodine?
We found no agar-specific figure in the sources we read. Some seaweeds are very high in iodine, so people with thyroid disease should ask a clinician. [6] [8]
Can I eat dry agar flakes straight from the packet?
We would not. Agar swells, and one case report links an agar bezoar to a blocked stomach pouch. [4]
References
- U.S. Department of Agriculture. FoodData Central: Seaweed, agar, dried (SR Legacy, FDC 170090). April 2018 release. Read 2026-10-24.
- U.S. Department of Agriculture. FoodData Central: Seaweed, agar, raw (SR Legacy, FDC 169280). April 2018 release. Read 2026-10-24.
- EFSA ANS Panel. Re-evaluation of agar (E 406) as a food additive. EFSA Journal 2016 (abstract read via Europe PMC search: link%20as%20a%20food%20additive%22)). Read 2026-10-24.
- Gero D, Chosidow D, Marmuse JP. An unusual cause of solid food intolerance and gastric pouch dilation 5 years after Roux-en-Y gastric bypass: agar-agar bezoar. Surg Obes Relat Dis 2015 (title, keywords and index terms read; no abstract available). Read 2026-10-24.
- Cotas J et al. Seaweed polysaccharides: a rational approach for food safety studies. Mar Drugs 2025 (abstract read). Read 2026-10-24.
- EFSA. Dietary exposure to heavy metals and iodine intake via consumption of seaweeds and halophytes in the European population. EFSA Journal 2023 (abstract read). Read 2026-10-24.
- Aoe S et al. Effects of daily kombu intake on body composition, blood pressure and fecal microbiota in healthy adult Japanese. Food Sci Nutr 2025 (abstract read via Europe PMC). Read 2026-10-24.
- NHS. Vitamins and minerals: Iodine. Read 2026-10-24.
- Frontier Co-op. Agar agar powder product label text (swelling and choking warning, as shown in a search summary of the product page; label statement only, not independent evidence). Read 2026-10-24 via search results.
- Vaughan K et al. Effect of brown seaweed on plasma glucose in healthy, at-risk, and type 2 diabetic individuals: systematic review and meta-analysis. Nutr Rev 2022 (abstract read via Europe PMC). Read 2026-10-24.