By Mark Faries, PhD
Howdy, I’m Dr. Mark Faries and I am dedicated to separating fact from fiction regarding topics of exercise and healthful eating.
Glucomannan, the famous ‘super-fiber’ got a major boost in 2015, when a review promoted its benefit in weight loss. But is this claim fact or fiction?
Glucomannan’s sponge-like effect in the digestive tract most likely comes from the overly hyped ingredient called amorphophallus konjac. It contains a fiber that dissolves in water and ferments somewhat like yeast in the colon. This substance is taken from an elephant yam, native to Asia.
Glucomannan has been endorsed by many as the super-fiber, because it can reportedly absorb 50% of its weight in water. So it creates a ‘mass-effect’ of this thick sticky, gel-like mass that forms in the stomach.
If you’ve ever seen what happens when you put water in a glass with Metamucil or psyllium husk in it, this is a similar effect. Now, imagine (or not) that gel-like mass eking its way through your stomach, intestines and colon.
The claims regard glucomannan’s absorption of water and its proposed abilities to: —Provide a sense of fullness.
—Bulk up food in your gut, so you cannot eat as much – thus reducing your energy intake.
—Lowering the weight ratio of food (much like vegetables do already).
Well, the hype for glucomannan became extraordinary when a review appeared to show in favor of it for weight loss. However, soon after the publication, the authors were made aware of some errors in the manuscript, and had to send a letter to the editor to fix these corrections.
In the letter, the authors state: “After correction with the new data, it turned out that after 2 weeks there is a statistically significant difference in favor of placebo, and in line with previously reported results, no statistically significant difference in effect after 8 weeks is observed. Similar to the difference in weight loss between study groups, BMI change seem to have little clinical significance due to very small values, in spite of the reported statistically significant effect.”
In summary, this review found that glucomannan was not more effective than a placebo. No differences in change in body fat, total fat mass, and waist and hip circumference, alongside no differences in perceived appetite or energy intake with a 12-week intervention.
I recommend that we enjoy the many wonderful benefits of fiber through beans, flax, vegetables, whole grains, nuts and fruit. Start slowly, and shoot for around 25-45 grams of fiber per day. So the claim that glucomannan is a super fiber essentially needs clarification. However, the claim that glucomannan will promote large amounts of weight loss is busted.
Glucomannan and obesity: a critical review. Keithley J, Swanson B. Altern There Health Med. 2005 Nov-Dec;11(6):30-4. Review.
The effect of glucomannan on body weight in overweight or obese children and adults: a systematic review of randomized controlled trials. Zalewski BM, Chmielewska A, Szajewska H. Nutrition. 2015 Mar;31(3):437-42.e2. doi: 10.1016/j.nut.2014.09.004. Epub 2014 Nov 25. Review.
Correction of data errors and reanalysis of “The effect of glucomannan on body weight in overweight or obese children and adults: a systematic review of randomized controlled trials”. Zalewski BM, Chmielewska A, Szajewska H, Keithley JK, Li P, Goldsby TU, Allison DB. Nutrition. 2015 Jul-Aug;31(7-8):1056-7. doi: 10.1016/j.nut.2015.02.008. Epub 2015 Mar 5.
