Glucomannan: A 'Super-Fiber'?

Glucomannan, the famous 'super-fiber' got a major boost this March (2015), when a review promoted its benefit in weight loss. However, a lot has happened since then!

To some degree, this is an update to a previous blog on Fiber and Weight Loss. As noted in that blog, certain products, such as Skinny Fiber, endorse an incredible 'sponge-like' effect that apparently can absorb anything from water, to fat, to evil spirits. 

Glucomannan (GM)

This sponge-like effect most likely comes from the overly-hyped ingredient glucomannan (amorphophallus konjac), which contains a soluble, fermentable (fermented in colon) fiber taken from an elephant yam, native to Asia. 

GM has been endorsed by many as the super-fiber, because it can reportedly absorb 50% of its weight in water, thus creating a 'mass-effect' of a viscous, gel-like mass that forms in the stomach.

Here is a video of what a Skinny Fiber pill does in a glass of water. Clearly, those of us who have made a glass of Metamucil or psyllium husk, we have seen a similar effect. Now, imagine (or not) that gel-like mass eeking its way through your stomach, intestines, and colon.

Recent Popularity

GM has been in the media a lot over the past few years, including popular TV media and endorsements from high-profile people. The endorsements surround GM'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 energy intake

* Lower energy to weight ratio of food (much like vegetables do already)

However, until recently, the research has shown minimal effects of 2-4 grams per day (usually 1 gram taken 3 times per day) on weight loss.¹ It received hype, because this earlier research review made the following conclusion, "2-4 g per day resulted in significant weight loss in mostly overweight and obese populations."

The problem was that "significance" refers to statistical significance, not how significant (dramatic, large) the weight loss was, as most people understood it. The average weight loss was only about 4 pounds over approximately 2 months. Good results, but clearly, nothing magical.

Oops!

Well, the hype for GM became extraordinary recently (March 2015) when a review appeared to show in favor of GM for weight loss.² However, soon after 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.

I commend the authors and others for catching and fixing the errors. 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 GM was not more effective than a placebo.

• Only 1 of 3 studies found a difference in weight loss versus a placebo after 8 or 12 weeks.
• No differences in change in body mass index (BMI)
• No differences in change in body fat, total fat mass, and waist and hip circumference
• No differences in perceived appetite No differences in energy intake with a 12-week intervention

Conclusion

I am not sure I would call GM "super" just yet, and it is clearly not a magical weight loss pill. Future research will provide a better understanding of GM.

However, I do think fiber and its many wonderful health benefits are super, but we do not have to get it through a fancy pill, or specific sugar from a yam flower in Asia.

We can 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/day.

Get Fiber in Food = "Dietary Fiber"

A fiber supplement, such as Skinny Fiber, gives us about 3-4 grams of fiber per serving. As a comparison:

Raspberries, 1 cup = 8 grams of fiber
Pear, with skin = 5.5 grams
Apple, with skin = 4.4 grams
Green Peas, 1 cup = 8.8 grams
Broccoli (boiled), 1 cup = 5.1 grams

Here are some more high fiber foods.

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References

1. Keithley, J. K., & Swanson, B. (2005). Glucomannan and obesity: A critical review. Alternative Therapies in Health and Medicine, 11(6), 30-34.
2. Zalewski, B. M., Chmielewska, A., & Szajewska, H. (2014). The effect of glucomannan on body weight in overweight or obese children and adults: A systematic review of randomized controlled trials. Nutrition, 31, 437-442.