Does glucomannan work for weight loss?
Not by much, if at all. Across 8 trials in people with overweight, it beat dummy pills by 0.22 kg, about an apple’s weight. But it does lower one number on a blood test.
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Does glucomannan help you lose weight?
Not by much. A 2014 review pooled 8 trials in people with overweight or obesity. Glucomannan gave 0.22 kg more loss than a dummy pill.
That gap was too small to tell apart from chance. The authors said the trials don’t show real weight loss.
Sources: NHS; Sood 2008; Onakpoya 2014
The best result, 0.79 kg, is a total over a whole trial, not a weekly loss. A steady week of eating less can match it.
Bought it to feel full? A US trial gave 53 adults with overweight glucomannan or dummy capsules before each meal for 8 weeks. It made no clear difference to weight, hunger or fullness.
Your move: if you try it, treat it as a small extra to eating less, not the plan itself.
What is glucomannan and how do you take it?
Glucomannan is a fibre from the root of the konjac plant, also called elephant yam. In water it swells to many times its size and turns thick, like wallpaper paste.
UK rules let a product claim it helps weight loss only on set conditions. Each portion must hold 1 g, and the label must explain how to take it.
The dose behind the weight loss claim
- 1
1 g at a time
Three doses a day, so 3 g in total.
- 2
With water
Take each dose with 1 to 2 glasses of water.
- 3
Before meals
Take it before meals.
- 4
Fewer calories
The claim only holds alongside a lower-calorie diet.
Check the label of yours. If one capsule holds less than 1 g, you may need more than one per dose.
Is glucomannan safe?
The side effects reported in trials were tummy trouble. The big risk is choking, so every label making a claim must carry a choking warning.
| Problem | What’s known | What to do |
|---|---|---|
| Choking or a blocked food pipe | It swells fast. One woman had a delayed blockage after a glucomannan diet aid. | Take it with plenty of water. Skip it if you have trouble swallowing. |
| Tummy pain, diarrhoea or constipation | Reported in weight loss trials. | Stop taking it if it upsets you. |
| Other medicines | It may change how well some medicines get into your body. | Ask your pharmacist before you start. |
Sources: UK claims register; Vanderbeek 2007; Onakpoya 2014
The woman with the blockage had a narrowing in her food pipe already. The report warns of extra danger if you’ve had problems in your upper gut.
On diabetes medicine? Glucomannan cut fasting blood sugar a little in trials, so ask your GP or pharmacist first. Never stop or change a prescribed medicine without your prescriber.
Does glucomannan lower cholesterol?
Yes, and this is where it does best. That number is your LDL cholesterol, one part of what the NHS calls bad cholesterol (non-HDL).
A 2017 review pooled 12 studies. About 3 g a day cut LDL by about 10% and non-HDL by about 7%.
UK rules allow a cholesterol claim only for products giving 4 g a day. No source we found shows it cuts heart attacks or strokes.
Your move: if cholesterol is your worry, read about LDL cholesterol first. Then compare glucomannan with psyllium husk and other cholesterol supplements.
What works better for weight loss?
Eating fewer calories than you use. The NHS says losing just 5 to 10% of your body weight can improve your health.
NHS steps that do more than a fibre capsule
- Eat and drink fewer calories than your body uses.
- Aim to lose 0.5 to 1 kg a week, steadily.
- Cut down on alcohol, which is high in calories.
- Get active for 45 to 60 minutes a day, in short bursts if that’s easier.
- Build up to 30 g of fibre a day from food, such as oats, beans and wholegrains.
- Weigh yourself regularly to check how you’re getting on.
Sources: NHS: obesity treatment; NHS: fibre
Work out your own number with calories to lose weight. Most adults eat about 20 g of fibre, so see how much fibre you need.
Weighing up other pills? See natural weight loss supplements. For support from people, see weight loss programmes.
When to speak to a GP
- Something feels stuck in your throat or food pipe, or you cough, choke or feel short of breath after eating or drinking. Ask for an urgent GP appointment or call 111.
- You have trouble swallowing. Don’t take glucomannan. Ask for an urgent GP appointment or call 111.
- You take medicines, including for diabetes. Ask before you start.
- You’re overweight and want help to lose weight, or your waist is more than half your height.
- You have, or think you may have, an eating disorder, such as binge eating.
A GP can refer you to a weight management programme, and some people can get weight loss medicines or surgery.