Agar is a natural substance extracted from red seaweeds that are found in waters throughout the world. Agar, a tasteless substance, has been used as a food ingredient for centuries. Agar readily forms a gel and is used as a stabilizer, bulking, thickening and gelling agent, and food additive.
Agar is a rich source of water-soluble, indigestible fiber. In the digestive tract, it absorbs water, increases bulk, and stimulates large bowel muscle contractions. Agar's most common therapeutic use has been as a laxative, and it has been used for decades as a daily treatment for chronic constipation. Agar is used in a variety of commercial applications, including production of cloth, paper, and cosmetics. More recently, agar has been used in scientific research laboratories to grow bacteria for use in experiments.
Agar has been studied in several clinical trials as a possible treatment for newborn hyperbilirubinemia, a condition characterized by high levels of the pigment bilirubin in the blood. High levels of bilirubin may result in jaundice, which is a yellow color in the skin and whites of the eyes. Agar has also been investigated to determine if it might have a beneficial effect on glucose intolerance in type 2 diabetes mellitus.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Preliminary evidence suggests that a diet supplemented with agar may have a beneficial effect on blood sugar and glucose intolerance. However, a diet supplemented with agar may not be significantly better than a low-calorie diet alone. Additional research is needed before a conclusion may be made.
Hyperbilirubinemia in newborns is a condition characterized by high levels of the pigment bilirubin in the blood. Sufficiently high levels of bilirubin may result in jaundice, or yellow color in the skin and whites of the eyes. Agar has been studied to determine if might be effective in the treatment of hyperbilirubinemia in newborns, but results have been mixed. Further research is required before a conclusion may be made.
* Key to grades
A: Strong scientific evidence for this use B: Good scientific evidence for this use C: Unclear scientific evidence for this use D: Fair scientific evidence for this use (it may not work) F: Strong scientific evidence against this use (it likley does not work)
Tradition / Theory
The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.
Antioxidant, constipation, hyperlipidemia (high levels of fats in the blood), obesity.
For general use, 4-16 grams have been taken by mouth once or twice daily with 250 milliliters of water. Two teaspoons of agar powder have been taken by mouth with eight or more ounces of liquid two to three times daily.
For diabetes, 180 grams of agar gel (Slim Kanten®) have been taken by mouth daily with the evening meal for four weeks.
Children (under 18 years old)
For jaundice, agar has been taken by mouth in milk, alone, and in conjunction with phototherapy. Doses of 2,625-16,000 milligrams in four to eight divided doses have been taken by mouth. Doses of 600-1,000 milligrams per kilogram body weight in divided doses have also been taken by mouth.
The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Avoid in patients with allergy or hypersensitivity to agar, its components, red seaweed, or related species.
Side Effects and Warnings
Agar is likely safe when consumed in normal dietary amounts.
Side effects may include gastrointestinal irritation, pain, and diarrhea when agar is given in powdered form in large doses.
Phytobezoars, which are rarely occurring concentrations of fruit and vegetable fibers in the gastrointestinal tract, have been reported following ingestion of high-fiber foods such as agar.
Agar products may delay stomach emptying time and reduce the absorption of some drugs, herbs, and supplements. It is advised that these agents and agar be taken at different times to minimize potential interactions.
Agar may reduce body weight and body mass index (BMI).
Agar may lower blood sugar levels. Caution is advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.
Agar may affect blood cholesterol levels. Use with caution in individuals with high levels of fats in the blood (hyperlipidemia) and those taking drugs, herbs, or supplements to treat this condition.
Use with caution because agar and other fermentable fiber supplements enhanced tumor development in studies that chemically induced colon cancer in experimental animals.
Use with caution in individuals taking laxatives, as use of agar with laxatives may have additive effects.
Avoid in patients with bowel obstruction or swallowing difficulties, as agar use may worsen esophageal or bowel obstruction, particularly when taken with insufficient amounts of fluid.
Avoid in pregnant or breastfeeding women due to a lack of available scientific evidence.
Avoid in patients with an allergy/hypersensitivity to agar, its constituents, red seaweed, or related species.
Pregnancy and Breastfeeding
Avoid in pregnant or breastfeeding women due to a lack of available scientific evidence.
Agar may lower blood sugar levels. Caution is advised when using medications that may also lower blood sugar. Patients taking insulin or drugs for diabetes by mouth should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
Agar products may delay stomach emptying time and reduce the absorption of some drugs. It is advised that these agents and agar be taken at different times to minimize potential interactions.
Agar may also in interact with anticancer drugs, antiobesity agents, cholesterol-lowering drugs, and laxatives.
Interactions with Herbs and Dietary Supplements
Agar may lower blood sugar levels. Caution is advised when using herbs or supplements that may also lower blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment.
Agar products may delay stomach emptying time and reduce the absorption of some herbs and supplements. It is advised that these agents and agar be taken at different times to minimize potential interactions.
Agar may also interact with anticancer agents, antiobesity herbs and supplements, antioxidants, cholesterol-lowering herbs and supplements, fiber-containing foods, laxative herbs and supplements, and zinc.
Blum D, Etienne J. Agar in control of hyperbilirubinemia. J Pediatr 1973;83(2):345.
Calvert R, Schneeman BO, Satchithanandam S, et al. Dietary fiber and intestinal adaptation: effects on intestinal and pancreatic digestive enzyme activities. Am J Clin Nutr 1985;41(6):1249-1256.
Dennery PA. Pharmacological interventions for the treatment of neonatal jaundice. Semin Neonatol 2002;7(2):111-119.
Ebbesen F, Moller J. Agar ingestion combined with phototherapy in jaundiced newborn infants. Biol Neonate 1977;31(1-2):7-9.
Holt S, Heading RC, Carter DC, et al. Effect of gel fibre on gastric emptying and absorption of glucose and paracetamol. Lancet 1979;1(8117):636-639.
Kaneko K, Nishida K, Yatsuda J, et al. Effect of fiber on protein, fat and calcium digestibilities and fecal cholesterol excretion. J Nutr Sci Vitaminol (Tokyo) 1986;32(3):317-325.
Maeda H, Yamamoto R, Hirao K, et al. Effects of agar (kanten) diet on obese patients with impaired glucose tolerance and type 2 diabetes. Diabetes Obes Metab 2005;7(1):40-46.
Meloni T, Costa S, Corti R, et al. Agar in control of hyperbilirubinemia of full-term newborn infants with erythrocyte G-6-PD deficiency. Biol Neonate 1978;34(5-6):295-298.
Minekus M, Jelier M, Xiao JZ, et al. Effect of partially hydrolyzed guar gum (PHGG) on the bioaccessibility of fat and cholesterol. Biosci Biotechnol Biochem 2005;69(5):932-938.
Odell GB, Gutcher GR, Whitington PF, et al. Enteral administration of agar as an effective adjunct to phototherapy of neonatal hyperbilirubinemia. Pediatr Res 1983;17(10):810-814.
Osada T, Shibuya T, Kodani T, et al. Obstructing small bowel bezoars due to an agar diet: diagnosis using double balloon enteroscopy. Intern Med 2008;47(7):617-620.
Sanaka M, Yamamoto T, Anjiki H, et al. Effects of agar and pectin on gastric emptying and post-prandial glycaemic profiles in healthy human volunteers. Clin Exp Pharmacol Physiol 2007;34(11):1151-1155.
Schellong G, Quakernack K, Fuhrmans B. [The influence of agar feeding on serum bilirubin in the physiologic jaundice of the newbron  infant (author's transl)]. Z Geburtshilfe Perinatol 1974;178(1):34-39.
Tsai AC, Elias J, Kelley JJ, et al. Influence of certain dietary fibers on serum and tissue cholesterol levels in rats. J Nutr 1976;106(1):118-123.
Wilmshurst P, Crawley JC. The measurement of gastric transit time in obese subjects using 24Na and the effects of energy content and guar gum on gastric emptying and satiety. Br J Nutr 1980;44(1):1-6.
The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.