Glucomannan is a dietary fiber that absorbs water, forming a “viscous gel-like mass”¹ that makes the user feel full as it passes through your intestines.  This practice has been supported by various studies:

This study:

At doses of 2-4 g per day, GM was well-tolerated and resulted in significant weight loss in overweight and obese individuals.

And this study:

An eight-week double-blind trial was conducted to test purified glucomannan fiber as a food supplement in 20 obese subjects. Glucomannan fiber (from konjac root) or placebo was given in 1-g doses (two 500 mg capsules) with 8 oz water, 1 h prior to each of three meals per d. Subjects were instructed not to change their eating or exercise patterns. Results showed a significant mean weight loss (5.5 lbs) using glucomannan over an eight-week period. Serum cholesterol and low-density lipoprotein cholesterol were significantly reduced (21.7 and 15.0 mg/dl respectively) in the glucomannan treated group. No adverse reactions to glucomannan were reported.

When you’re looking at Glucomannan as included in a diet pill you may be considering just remember to look at the total amount included for the day.  These studies all used 2-4 grams of Glucomannan every day.  I don’t know what the lowest effective does would be, but keep that in mind.  Whenever there’s a new ingredient that is clinically proven to actually work, diet pill companies will include the smallest amount of it in their pill and then begin to cite the clinical study as backing their pill.  Shameless.

1. http://en.wikipedia.org/wiki/Glucomannan [↩]