Principal Proposed Uses

Other Proposed Uses

Glucomannan is a dietary fiber derived from the tubers of Amorphophallus konjac . Konjac flour (made from these tubers) is used to make a jelly called konyaku, a common food product in Japan. Fiber-containing foods, such as oats, are known to help reduce cholesterol and improve constipation and may also help regulate blood sugar and assist in weight reduction by creating a feeling of fullness. However, many people have a hard time consuming enough fiber from food, so turn to fiber supplements, such as guar gum and pectin, to help fulfill their daily requirements. Glucomannan offers one advantage over these forms of fiber: much smaller doses are necessary. When glucomannan is placed in water, it can swell up to 17 times its original volume. These qualities make it potentially quite convenient as a fiber supplement.


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

Therapeutic Dosages

Most of the studies described here used 3 to 5 g per day in divided doses before meals. However, there are concerns regarding the form of glucomannan used (see Safety Issues below).

Therapeutic Uses

Several small controlled studies have found glucomannan to be effective for improving the cholesterol profile. 1-7,37 Glucomannan appears to reduce LDL ("bad") cholesterol and, according to some studies, increase HDL ("good") cholesterol. In addition, it may improve blood pressure . By expanding in the stomach, glucomannan might be useful for people trying to lose weight. Many people report a feeling of fullness after taking glucomannan, and some studies found a significant weight loss among those taking glucomannan compared to those on placebo . 8-12 However, not all studies of glucomannan for weight loss have had positive results. 13,14 Glucomannan may also help the body to regulate blood sugar levels, and therefore could be helpful in treating diabetes . 15,16,37 Additionally, glucomannan might be helpful for individuals who experience episodes of low blood sugar following stomach surgery. 17 Like other dietary fibers, glucomannan may help treat constipation . 18,19,38,40Hyperthyroidism is a state in which levels of thyroid hormone are too high. A preliminary trial found some evidence that when glucomannan is added to standard treatment, normal thyroid hormone levels are restored more rapidly. 39

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