Although commonly used as a food additive, glucomannan may play a much more important role in nutrition.
Studies show glucomannan has a large impact on diabetes, constipation, cholesterol, and body weight.
However, like any nutrient, glucomannan exhibits some negative effects in certain users as well.
Effect on Diabetes
Glucomannan improves cholesterol and glucose levels, thereby treating diabetes symptoms. In one study, glucomannan improved blood lipid levels by enhancing fecal excretion of steroids.
Glucomannan also reduced aspects that lower metabolic control and raise risk of heart disease in diabetes patients, including cholesterol and blood pressure. This may improve glycemic control in those with type 2 diabetes.
However, those with diabetes should be careful when taking glucomannan, as it may interact with anti-diabetes drugs. Because both diabetes medications and glucomannan lower blood sugar, the combination may cause hypoglycemia, or extremely low blood sugar.
Low blood sugar may cause symptoms such as trembling, rapid heart rate, headache, dizziness, or loss of consciousness. It’s important for diabetes patients to monitor their blood sugar levels at any time, but particularly when taking glucomannan along with medications.
Effect on Constipation
Soluble fibers like glucomannan treat constipation by slowing digestion and optimizing nutrient absorption. In one 2-month study, glucomannan treatment improved constipation symptoms—such as frequency of bowel movements and abdominal symptoms—without relevant side effects.
However, glucomannan may not help all people with constipation. Those with conditions such as slow transit or pelvic floor dysfunction may react negatively to glucomannan. WebMD recommends talking to a doctor “if you have a sudden change in frequency of bowel movements and develop acute constipation.”
Effect on Cholesterol
Glucomannan has the impressive ability to lower cholesterol levels. In one study, it reduced total cholesterol, LDL (“bad”) cholesterol, and blood pressure, reducing risk of heart disease and stroke.
If you are taking medications to lower blood pressure., the combination with glucomannan may cause it to drop too low,causing inadequate blood flow to the brain and heart. This could cause dizziness or lightheadedness.
Glucomannan may also interact with cholesterol-lowering medications. Thus, it’s important to take glucomannan at least one hour after other medications to avoid interference.
Effect on Weight Loss
Fibers like glucomannan can fill up your stomach and cause you to feel full, reducing caloric intake. In one 8-week double-blind trial, 20 obese subjects lost an average of 5.5 lbs. with the help of glucomannan.
Although this isn’t groundbreaking weight loss, it’s definitely beneficial. In addition, the cholesterol-lowering properties of glucomannan improve other obesity-related health factors.
Glucomannan Blockage Risk
Some forms of glucomannan, particularly the solid tablet version, could block the throat and intestines and cause choking. It’s important to drink at least 8 ounces of water while taking glucomannan.
Interactions with Medications
As was mentioned, glucomannan may interact with certain medications, such as medicines that lower cholesterol or blood pressure.
Also, glucomannan may lower effectiveness of all oral medications. This is because it absorbs substances, including medications. You should take glucomannan at least an hour after other medications to avoid this side effect.
What’s the Proper Dosage of Glucomannan?
Using the correct dosage minimizes side effects, but the right dosage depends on your tolerance and medical needs.
For type 2 diabetes with high cholesterol, a daily dosage between 3.6 to 10.6 g is typically used.
Talk with your doctor to find out what’s right for you.
-  Hsiao-Ling Chen et al. “Konjac Supplement Alleviated Hypercholesterolemia and Hyperglycemia in Type 2 Diabetic Subjects—A Randomized Double-Blind Trial.” J Am Coll Nutr. 2003; 22 (1): 36-42.
-  Vuksan V. et al.“Konjac-mannan (glucomannan) improves glycemia and other associated risk factors for coronary heart disease in type 2 diabetes. A randomized controlled metabolic trial” Diabetes Care. 1999; 22 (6): 913-9.
-  “Glucomannan.” WebMD.com.
-  “When Blood Sugar Is Too Low.” KidsHealth.org.
-  Passaretti S. et al.“Action of glucomannans on complaints in patients affected with chronic constipation: a multicentric clinical evaluation.” Ital J Gastroenterol. 1991; 23 (7): 421-5.
-  “Dietary Fiber for Constipation.” WebMD.com.
-  Arvill A, Bodin L.“Effect of short-term ingestion of konjac glucomannan on serum cholesterol in healthy men.” Am J Clin Nutr. 1995; 61 (3): 585-9.
-  “Understanding Low Blood Pressure – the Basics.” WebMD.com.
-  Walsh DE et al.“Effect of glucomannan on obese patients: a clinical study.”Int J Obes. 1984; 8 (4): 289-93.
-  “Health Canada Advises Canadians that Natural Health Products containing Glucomannan May Cause Serious Choking if Used with Insufficient Fluid.” Healthy Canadians. 29 January 2010.