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Glucomannan: Fat-Fighting Fiber or Fraudulent Fad?

By David Grotto, RD, LDNJune 4, 2012
From the WebMD Archives

The noodles are sold under the names “Tofu Shiratake,” “Miracle,” or “Zero” noodles and are made from the roots of the ancient elephant yam, better known as the Asian Konjac plant. Glucomannan, the viscous soluble dietary fiber found in the Konjac root, is the secret behind the zero-calorie claim and what makes these noodles so appealing for helping with weight loss efforts.You may have seen noodles sold in grocery and health food stores claiming to have very few to zero calories per serving. Are these noodles too good to be true? What does science have to say regarding their claims of no calories or use as an aid to weight loss?

Glucomannan is also sold as a dietary supplement in powder, capsule, and tablet forms, either as a single ingredient or in combination with other fibers or weight loss aids. Abundant claims have been made about glucomannan’s ability to promote weight loss.

A 2003 report from the Food and Trade Commission (FTC) states that as much as “55 percent of advertising for weight loss products and services contained false or unsupported efficacy claims.” One of the products mentioned in the report contained glucomannan as an ingredient and also made an unsupported claim for weight loss. Nine of the ten experts that served on the panel in the report stated, “Given the current state of scientific knowledge, no nonprescription drug, dietary supplement, cream, wrap, device, or patch would cause users to lose weight without reducing caloric intake and/or increasing physical activity.” So what does the science have to say about the role of glucomannan in weight loss?

Is it safe? The most common complaint of taking glucomannan as a supplement in several studies was transient bloating and gas. Researchers feel this may be due to the sudden introduction of fiber into a low-fiber diet. Most were not dissuaded by this mild inconvenience and within a few weeks, these side effects subsided. Beyond that, glucomannan appears safe.

Does it work? Preliminary evidence suggests that glucomannan may promote weight loss at doses of 1-4 grams per day by promoting satiety and by blocking some calories from being absorbed in the body. Research has shown that the more viscous or gel-like a fiber is, the better it seems to work on the three mechanisms that affect appetite: mechanical (physically taking up rooms in the gut); hormonal (controlling appetite hormones), and transition time (slowing down the absorption of food).

In a study that assessed appetite ratings of 31 healthy girl and boy adolescents that were not overweight or obese, each participant was asked to consume one of three different types of a high-fiber beverage 90 minutes before being presented with an all-you-can-eat pizza experience. Then on separate days, they tried the remaining fiber beverages. All products produced decreased appetite scores; however, the blend of glucomannan, xanthan, and sodium alginate did a better job of reducing pizza consumption for all three mechanisms of appetite compared to second place, straight up glucomannan.

Looking at the effects of glucomannan alone or in combination with other fibers on an older, overweight but not obese population, 165 male and female participants were either given a placebo; glucomannan; or a combination of glucomannan, guar gum, and alginate (derived from seaweed) for 5 weeks. All subjects followed a 1200 calorie diet, too. Fiber tablets were taken 15 minutes before meals and additionally at 3pm. All fiber products did better in promoting weight loss compared to the placebo group, but no one fiber proved more effective than the other. Adherence to the diet was also an unknown in the study.

Twenty-nine overweight and obese female and male volunteers were given a proprietary blend of fibers that included glucomannan in a non-controlled or randomized study to assess its effect on appetite. All participants were given instruction on a healthy diet and exercise program but were not assigned to a specific calorie level. Participants consumed the fiber mixed in water about 5-10 minutes prior to meals, 2-3 times daily for 14 weeks. Significant reductions in weight, waist measurement, and body fat were observed as well as reductions in total and LDL cholesterol and fasting insulin.

Glucomannan may have limited value in helping to manage weight but it appears to have a greater benefit when combined with a healthy diet and exercise program. Forty-two sedentary and overweight men and women received a lower dose of glucomannan (compared to other studies) taken before two meals every day that were not calorie controlled. Half of the group participated in total body exercise for one hour three times a week while the other group remained sedentary. After 8 weeks, both groups reduced their calorie intake, lost weight and fat while also improving their blood lipids. The exercise group, however, showed the greatest improvement in lipids and experienced up o a 63% greater fat loss for men and 50% greater fat loss in women when compared to the non-exercise group! No further reductions in weight loss were seen, however, which may be explained by increases in lean body mass. Leptin, a protein peptide secreted by fat cells which helps control appetite, were reduced in both groups but to a much greater extent in the exercise group. Blood lipid reductions such as cholesterol along and triglycerides and other health markers tied to metabolic syndrome have also been observed in other research.

Is it expensive? Surprisingly, compared to the price of glucomannan supplements, the cost of shiratake noodles are in the same ballpark. An 84-gram bag (9 ounces) yields a total of 9 grams of soluble fiber (3 grams per serving, 3 servings in a bag). Cost per bag? If you bought a case of 24 online of the angel hair pasta style, including shipping and handling, it would set you back $1.46 per bag. The going rate for the supplement form of glucomannan ranges from $1.20-$2.10 per 9 grams of soluble fiber. Keep in mind that many of the studies used a range of 1-4 grams so the cost would be even less.

Bottom line? Based on the bulk of the science, studies have demonstrated 1-5 grams of glucomannan consumed daily have enhanced weight loss effort. Like the FTC report mentioned earlier, glucomannan probably won’t perform miracles all by itself, but studies have shown it may be a great companion to a healthy calorie management program via healthy portion sizes combined with physical activity.

Where can I get more information? There are a few websites out there that give some background and tips and feature photos of Konjac root and glucomannan powder.

Have you tried these noodles or taken the glucomannan supplements? Let me know if you like the noodles and how you prepare them or if you have had any success with the supplement form.

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