Hypertension and Glucomannan

Glucomannan is a dietary fiber derived from the tubers of Amorphophallus konjac. Glucomannan and other forms of dietary fiber may help improve blood pressure and cholesterol levels.

There are a number of ways that fiber such as glucomannan may help lower blood pressure, and the exact actions are not yet clear.

Read more details about Glucomannan.

In a double-blind study , 63 people were given either 3.9 g per day of glucomannan or placebo for 4 weeks and then switched to the other treatment.² While taking glucomannan, participants showed significant reductions in total cholesterol, LDL cholesterol, and triglycerides, as compared to placebo. In addition, their systolic blood pressure (the upper number in the blood pressure reading) was also reduced.

Participants in another study were given either 3 g per day of glucomannan or placebo over an 8-week period.³ The glucomannan group showed improvements in total and HDL cholesterol as well as a reduction in systolic blood pressure. Those taking glucomannan also lost weight, whereas the placebo group gained weight over the length of the trial.

Several other controlled studies have found similar results.⁴ And, in a mathematical review combining the results of 14 studies, glucomannan significantly reduced total and LDL cholesterol levels.⁵

Most of the studies described here used 3 to 4 g per day in divided doses before meals. However, there are concerns regarding the form of glucomannan used (see Safety Issues).

Although glucomannan can be derived from other sources such as yeast, most studies have used glucomannan purified from the konjac root.

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Safety Issues

In Japan, food products containing glucomannan have a long history of use and are believed to be safe. However, there are some concerns about taking glucomannan as a supplement.

Some people taking glucomannan complain of excess gas, stomach distension, or mild diarrhea. These symptoms usually abate within a couple of days of treatment or with a reduction of the dosage.

In a few cases, glucomannan tablets have caused obstruction of the esophagus when they expanded before reaching the stomach. ¹ In response to these reports, tablets of this type have been banned. Capsules, however, do not seem to pose the same risk because their casing prevents the glucomannan from contacting water until it reaches the stomach. The dramatic expansion of glucomannan has also raised some concerns that it could cause an obstruction in the intestines; nonetheless, as of yet, there have been no reports of this actually happening.

One option to offset all expansion risk is to mix glucomannan powder in water so that it expands before it is ingested; however, this strategy defeats the convenience of this form of fiber.

1. Gaudry P. Glucomanna diet tablets [letter]. Med J Aust. 1985;142:204.

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2. Reffo GC, Ghirardi PE, Forattani C. Double-blind evaluation of glucomannan versus placebo in postinfarcted patients after cardiac rehabilitation. Curr Res Ther. 1990;47:753-758.
3. Venter CS, Kruger HS, Vorster HH, et al. The effects of dietary fiber component konjac-glucomannan on serum cholesterol levels of hypercholesterolemic subjects. Hum Nutr Food Sci Nutr. 1987;41F:55-61.
4. 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. 88(4):1167-75.
5. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes. 8(4):289-93.