How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Glucomannan (konjac)
A soluble fibre derived from konjac. It slightly lowers LDL cholesterol (around 10% at 3 g per day), but the meta-analysis of weight trials finds no weight loss.
Benefits
- Lowers LDL cholesterol by about 10% and non-HDL cholesterol by about 7% (meta-analysis of 12 trials, 370 participants, around 3 g per day)
- In 63 healthy men, 3.9 g per day for 4 weeks: total cholesterol −10%, LDL −7.2%, triglycerides −23%
- In type 2 diabetics, fasting and post-meal blood glucose lower, as well as fasting insulin and fructosamine (meta-analysis, 440 patients)
- Slightly more frequent stools in constipated children (3 trials, 122 participants) and constipated adults (1.5 g three times a day); constipation symptoms improved in 8 weeks in taekwondo athletes
- Replacing part of a carbohydrate-rich meal with jellified konjac noodles reduced total energy intake, without the 16 participants eating more afterwards
Precautions
Glucomannan swells by absorbing water: a case of oesophageal obstruction has been published in a 37-year-old woman after taking a slimming product containing it, and the risk is described in people who have previously had oesophageal or stomach disorders. Abdominal discomfort, diarrhoea and constipation are reported in weight trials; in constipated children, abdominal pain was more frequent during certain weeks. In a trial of 96 overweight children, blood pressure was higher with glucomannan. In hyperthyroid patients on treatment, it lowered thyroid hormones: if you are taking thyroid medication, speak to your doctor about it. Limitations: for weight, the meta-analysis of 8 trials finds no difference compared to placebo, nor does the 8-week trial in 53 adults or the 12-week trial in 96 children; the 2.5 kg weight loss often cited comes from a 1984 trial in 20 people. In constipated children, a trial of 72 children performs no better than placebo.
Recommended dosage
Around 3 g per day, often taken in three doses of 1 to 1.5 g before each meal.
How to take it
- Dose: around 3 g per day in the LDL cholesterol meta-analysis, and 3 g per day in the 4-week trial in type 2 diabetics.
- Splitting: several trials give 1 to 1.5 g before each of the three meals.
- Duration: from 4 to 12 weeks in the trials of this profile.
- For weight loss: the meta-analysis of 8 trials sees no weight loss compared to placebo, nor does the trial at 1.33 g before each meal for 8 weeks.
- Form: capsules, powder, jellified konjac noodles and sweets have been tested; no study in this profile compares the forms against each other.
Did you know?
On cholesterol, the effect is seen in four weeks: in 63 healthy men, 3.9 g of glucomannan per day lowered total cholesterol by 10% and triglycerides by 23%, without changing their weight.
What the studies say
This systematic review and meta-analysis evaluated the impact of glucomannan supplementation on the lipid profile in adults, using randomized clinical trials. The results showed a significant decrease in total cholesterol, LDL cholesterol, and Apo B1. However, glucomannan did not alter triglyceride levels, HDL cholesterol levels, or other important lipid ratios.
Musazadeh V, Rostami RY, Moridpour AH, Hosseini ZB, Nikpayam O, Falahatzadeh M, Faghfouri AH. — BMC cardiovascular disorders (2024) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more