Mickie Cathers
Weight loss is big business with multiple supplements on the market advertising promising results. Glucomannan is one weight loss supplement gaining popularity in patients seeking to reduce cravings and control appetite as a way to lose weight. What’s behind the hype?
Background
Glucomannan is a water-soluble dietary fiber found in the root of the konjac plant. Konjac, also known as elephant yam, is grown in parts of Asia and is best known for its starchy bulb root, a tuber-like part of the stem that is used to make low-carb noodles and rice, similar to riced cauliflower. Shirataki noodles have a gelatinous texture and are commonly used in Japanese cooking.
In January 2020, FDA approved glucomannan for labeling as a dietary fiber. FDA determined that glucomannan met the standards of naturally occurring fibers in plants and that the available scientific evidence suggested that glucomannan can help reduce blood cholesterol.
Dietary fiber does more than alleviate constipation. A high-fiber diet helps maintain bowel health overall, lowers cholesterol levels, helps control blood glucose levels by slowing the absorption of glucose, and can aid in achieving a healthy weight. As fiber is more filling and energy-dense, it may lead people to eat less and feel satisfied longer.
Is there a benefit?
Much like other soluble fibers found in oats, chia seeds, apples, carrots, peas, beans, citrus fruits, barley, chicory root, and psyllium, the hypoglycemic and lipid-lowering effects of glucomannan are widely known.
A meta-analysis published February 15, 2023, in Nutrients evaluated the effects of glucomannan supplementation on blood lipid-related indicators, blood glucose-related indicators, BP, and bodyweight in patients suffering from T2D. Zhang and colleagues analyzed six randomized controlled trials evaluating glucomannan and T2D. The authors found statistical significance that glucomannan reduced total cholesterol, low-density lipoprotein levels, fasting blood glucose, fasting insulin, and serum fructosamine levels compared with the control groups.
Glucomannan is thought to aid in weight loss by forming a viscous gel in the stomach, slowing gastric emptying, and increasing the feeling of satiety and fullness. However, the data here are inconsistent. A September 2020 review in Obesity Medicine by Mohammadpour and colleagues evaluated six randomized clinical trials and concluded that glucomannan resulted in significant reduction in weight in studies over 8 weeks with more than 30 adults who are overweight and obese.
In contrast, an August 2019 randomized, double-blind, placebo-controlled trial published in the Journal of Pediatrics assessed the efficacy of glucomannan on the BMI of 96 children with overweight or obesity. Participants received 3 g/day of glucomannan or placebo for 12 weeks and were followed up for the next 12 weeks. The authors concluded that glucomannan supplementation compared with placebo had no effect on weight reduction.
A December 30, 2013, trial in the Journal of Obesity evaluated the safety and efficacy of glucomannan. Participants were randomly assigned to take 1.33 g of glucomannan or placebo with 8 oz of water one hour before breakfast, lunch, and dinner for 8 weeks. Results revealed no significant difference between glucomannan and placebo with respect to weight loss, body composition, and hunger/fullness in overweight and moderately obese individuals.
More trials are needed to assess any significant beneficial effect of glucomannan on body weight.
Dosage and availability
Glucomannan is available as gummies, powder, and capsules as well as mixed into supplemental powders advertised as detox blends for herbal cleanses and gut health support. As a powder, glucomannan can be used to thicken soups and sauces in much the same way cornstarch is commonly used. Shirataki noodles and riced konjac are available in Asian markets or the Asian food section of the supermarket. These products are so fiber-rich that their net carbs per serving are listed as zero, making them popular among those following a keto lifestyle. Glucomannan has also started showing up on the ingredients list of gluten-free baked goods.
Daily recommended fiber for adults ranges from 21 to 38 grams, but more than 90% of Americans do not meet recommended daily levels.
What to tell your patients
While it’s generally better to get one’s fiber through switching to whole grains and incorporating more fruits and vegetables into the diet, fiber supplements such as glucamannon are generally regarded as a safe addition. Caution patients to add supplemental fiber incrementally over a few weeks. Adverse effects of adding fiber too quickly include intestinal gas, abdominal bloating, and cramping. Advise patients to select supplements certified by credible organizations such as NSF International, ConsumerLab, or the US Pharmacopeial Convention.
Also counsel patients taking glucomannan to drink plenty of water. Be aware that the powder has the potential to be a choking hazard and block the stomach. ■