Professional Refreshers


January 11, 2017   /
Elaine M. Hinzey, RD, LDN

What is glucomannan?

Glucomannan is a sugar created from the root of the konjac plant. Glucomannan supplements are available in powder, capsule, and tablet form. In foods, glucomannan is used as a thickener or gelling agent.

What is glucomannan used for?
Claims state that glucomannan is useful for treating constipation and aids in blood glucose control, in weight loss, and for lowering cholesterol. Glucomannan is believed to absorb water in the stomach and intestines, which forms a bulky fiber that slows constipation and also may slow the absorption of sugar and cholesterol.

In a study published in 2008 in the British Journal of Nutrition, 200 overweight or obese patients were randomized to receive a mixture of fiber including glucomannan, either twice or three times daily, or a placebo. All of the women were put on an energy-restricted diet. Weight loss was higher after both doses of fiber compared to the placebo, but the changes were not statistically significant. Postprandial satiety was reported by those women receiving the fiber supplements.

The differences in low-density lipoprotein (LDL) cholesterol levels were significant, as were the changes in total cholesterol—high-density lipoprotein (HDL) cholesterol and HDL cholesterol:LDL cholesterol ratios. No effects on HDL cholesterol, glucose and insulin concentration, glucose tolerance, or high-sensitivity C-reactive protein were observed.

In a double-blind, randomized, placebo-controlled, crossover trial conducted in 36 children between 6 and 15 years of age with primary hypercholesterolemia, those who received glucomannan had a significant reduction in total cholesterol (5.1%) and LDL cholesterol (7.2%) as compared with placebo. However, no difference to HDL, triglycerides, apolipoprotein B, or apolipoprotein A-I concentrations was observed. The lipid-lowering effects of glucomannan were significantly greater in females when compared to males.

A meta-analysis published in the American Journal of Clinical Nutrition in 2008 looked at 14 studies and found that glucomannan significantly lowered total cholesterol, LDL cholesterol, triglycerides, body weight, and fasting blood glucose. Pediatric patients, patients receiving dietary modification, and patients with impaired glucose metabolism did not benefit from glucomannan to the same degree. The researchers found that glucomannan did not have an effect on HDL cholesterol or blood pressure.

I have diabetes. How much glucomannan should I take?
In scientific research, people with type 2 diabetes and high cholesterol have taken 3.6 to 10.6 grams/day. Most experts recommend taking it 15 minutes before eating.

Does taking a glucomannan supplement pose any risks?
Glucomannan powder and capsules are deemed “possibly safe” for most adults and children. However, solid tablets may cause blockages of the throat or intestines. Pregnant women and breastfeeding women should avoid taking glucomannan. Because glucomannan may decrease blood glucose, people with diabetes should use caution and check their blood glucose regularly when taking these products.

In addition, it is necessary to stop taking glucomannan at least 2 weeks before any scheduled surgeries. Because glucomannan absorbs substances from the stomach and intestines, it may decrease how much medicine your body absorbs, so it is important to take it at least 1 hour after taking any other medications.  Be sure to drink plenty of water when using glucomannan. Some people report experiencing flatulence, bloating, and abdominal cramping while using glucomannan.


Resources and recommended readings
Andersen CH. Glucomannan: the weight loss supplement Dr. Oz loves. website. Accessed October 21, 2013.

Glucomannan. WebMD website. Accessed October 21, 2013.

Guardamagna O, Abello F, Cagliero P, Visioli F. Could dyslipidemic children benefit from glucomannan intake? Nutrition. 2013;29(7-8):1060-1065. doi:10.1016/j.nut.2013.02.010.

Salas-Salvadó J, Farrés X, Luque X, et al; Fiber in Obesity-Study Group. Effect of two doses of a mixture of soluble fibres on body weight and metabolic variables in overweight or obese patients: a randomised trial. Br J Nutr. 2008;99(6):1380-1387. 

Sood N, Baker WL, Coleman CI. Effect of glucomannan on plasma lipid and glucose concentrations, body weight, and blood pressure: systematic review and meta-analysis. Am J Clin Nutr. 2008;88(4):1167-1175.