NOW Glucomannan 575 mg review

Our take: a good fibre sold for the wrong reason

There is nothing hidden in this bottle. Glucomannan from konjac root, 575 mg a capsule, three capsules a serving, a vegetable capsule and four named excipients. The manufacturer gives the botanical species, the water volume, the timing before meals and a real choking warning. On label quality alone this is well above what we usually review in this category.

The problem is the headline. The product page leads with "Healthy Weight Management", and that is the claim with the weakest support behind it. A meta-analysis of eight randomised trials found no statistically significant weight difference between glucomannan and placebo, and the NIH Office of Dietary Supplements concludes it has little to no effect on weight loss. The other two claims on the same page, regularity and cholesterol, are the ones the evidence supports better. That is the reverse of the order the page puts them in.

Then the arithmetic. The front says 575 mg, but the serving is three capsules. The panel says 60 servings, but the directions allow up to two servings a day, and at that rate the 180-capsule bottle lasts 30 days. Neither number is false, but a shopper who takes them at face value will be out by a factor of three or six.

It scores 5.8. If you want a capsule fibre for cholesterol or regularity and will drink the water, it is a sensible buy at a fair price. If you are buying it to lose weight, the trials suggest you will be disappointed.

This is a desk review of a published label and the research behind the ingredient. Nobody here has taken this product.

What is in the capsule, and what the label tells you

The Supplement Facts panel lists a serving of three veg capsules providing 1,725 mg of glucomannan from konjac root (Amorphophallus konjac), 2 g of dietary fibre, 2 g of total carbohydrate and 5 calories. The bottle holds 180 capsules, which the panel counts as 60 servings.

The other ingredients are hypromellose (the cellulose capsule), hydroxypropyl cellulose, silicon dioxide, microcrystalline cellulose and stearic acid from a vegetable source. These are standard fillers and flow agents, and all of them are named. The product is marked vegan, non-GMO, kosher and halal, and made without gluten, soy, dairy, eggs or nuts. It is produced in a facility that also handles those allergens.

The directions are more specific than most: "Take 3 capsules 1 to 2 times daily with at least 8 oz. of water 30 - 45 minutes before meal." The water volume is a safety requirement, and the timing before meals is how the satiety trials were run. Both are in the right place.

The numbers on the front, and what they cost

There are two gaps between what the bottle appears to say and what it means in use.

575 mg is one capsule, not one dose. The serving is 1,725 mg. A shopper comparing this with a product that states its strength per serving is comparing one third of a dose with a whole one.

60 servings is not 60 days at the upper dose. The directions allow one or two servings a day. At one serving the bottle lasts 60 days. At two, which is six capsules and 3,450 mg a day, it lasts 30.

At the manufacturer's price of $26.99 a capsule costs 15 cents, a serving costs 45 cents, and a day costs 45 to 90 cents depending on which end of the directions you follow. That is roughly $13.50 to $27 a month. For a capsule that is a fair price. It is not the cheapest way to buy soluble fibre, because a capsule format costs more per gram than a loose powder. What you are paying for is convenience.

To be clear, NOW is not hiding anything. The serving and the servings per container are both printed where the law requires them, and the dosing range is in the directions. But the product is sold on the front of the bottle, and that is where 575 mg sits.

The evidence, claim by claim

Glucomannan is one of the few ingredients where the research is reasonably clear, and it points in different directions for the three claims on this bottle. We grade each claim on its own, and our glucomannan evidence page sets out the grades.

Weight management: weak

The mechanism is plausible. Glucomannan absorbs many times its weight in water and forms a thick gel in the stomach, which adds bulk and slows emptying. The idea is that you feel fuller and eat less. Plausible mechanisms are cheap, though, and the outcome is what counts.

A 2014 systematic review and meta-analysis by Onakpoya and colleagues in the Journal of the American College of Nutrition pooled eight randomised trials. It found a weight difference against placebo of −0.22 kg, with a confidence interval running from −0.62 to +0.19 kg. That is not statistically significant, and it is small even at the optimistic end. A 2019 randomised controlled trial in children and adolescents with overweight, published in the Journal of Pediatrics, found no effect on weight at all.

The one authority that sounds more positive is the European Food Safety Authority. It approved the claim that glucomannan "in the context of an energy-restricted diet contributes to weight loss", with conditions: at least 3 g a day, split into three 1 g doses, each taken with one or two glasses of water before a meal. Look at what that claim actually covers. It applies to people who are already cutting calories, it describes a contribution rather than a cause, and it needs a dosing schedule this bottle's directions do not follow. It supports the ingredient as a minor aid to a diet, not as a weight-management product in its own right.

Cholesterol: moderate, and the best case for buying it

This is where glucomannan does best. A 2017 meta-analysis by Ho and colleagues in the American Journal of Clinical Nutrition pooled randomised trials in adults. It found that konjac glucomannan lowered LDL cholesterol by about 0.35 mmol/L, roughly 10 per cent, and non-HDL cholesterol by about 7 per cent, at around 3 g a day. EFSA separately accepts that glucomannan contributes to normal blood cholesterol at 4 g a day.

Those are real, modest effects, much like the other viscous fibres. NOW phrases the claim carefully: it "may also help to maintain serum lipid levels already within the healthy range". That is a structure–function claim, and it deliberately avoids promising to treat high cholesterol. It should not replace treatment where treatment is indicated.

Regularity: reasonable

As a bulk-forming soluble fibre, glucomannan does what fibre does, and that fits this use best. The evidence base is thinner than for psyllium, which has guideline support for chronic constipation. Our NOW Psyllium Husk Powder review covers that comparison in detail.

Is the dose right?

Partly. The label's daily range is 1,725 to 3,450 mg. At the upper end that clears the ~3 g used in the LDL meta-analysis, so for cholesterol the dose is reasonable if you take the full two servings.

It falls short in two ways. It never reaches the 4 g EFSA ties to its cholesterol claim, because that would take seven capsules and the label stops at six. And the directions give the dose as two large doses rather than three smaller ones before each meal, which is how EFSA's weight condition was framed. You could take the same six capsules as two before each of three meals and stay within the label's daily total. That would be your adjustment, though, not the label's instruction, and it would mean opening a bottle three times a day with 8 oz of water each time.

Safety: the choking warning is not a formality

Glucomannan swells fast. If it is taken with too little liquid, it can expand in the throat or oesophagus before it reaches the stomach. This has happened: Australia has banned glucomannan in tablet form since 1985 after a run of oesophageal obstruction cases. Capsules and powders are still sold there. Capsules dissolve differently from compressed tablets, but they carry the same basic risk if taken dry.

NOW's caution is clear and prominent: "Without drinking enough liquid the product may swell in the throat, causing blockage or choking. Avoid use if you ever had esophageal narrowing or swallowing difficulties." We would add three things the label does not spell out:

• Space it away from medication. A viscous gel can slow or reduce how other medicines are absorbed. A gap of at least an hour or two is standard advice, and a pharmacist can say exactly how long for what you take.
• Take care with diabetes medication. Viscous fibres slow how fast carbohydrate is absorbed. If you use glucose-lowering drugs, raise this with your prescriber before starting.
• Start low. Bloating, wind and cramping are common in the first weeks of any fibre. Starting at one serving a day and building up is kinder than starting at six capsules.

The label restricts the product to adults and asks anyone pregnant, nursing, on medication or with a medical condition to consult a physician first.

What buyers report

The Amazon listing shows 4.2 stars from 3,918 ratings, with more than a thousand bought in the past month. For a plain fibre capsule that is a solid rating on a large sample. Marketplace ratings measure satisfaction, not efficacy. They mix delivery, price and taste with everything else, and a high rating for a product bought mainly for weight loss says nothing about whether the weight came off because of it.

Who this is actually for

It makes sense for someone who wants to add a few grams of soluble fibre a day in capsule form, whether to nudge LDL cholesterol or to help with regularity, and who will reliably drink a full glass of water with every dose. For that person it is a clean, fully disclosed product at a fair price.

It makes less sense for someone who can manage a powder. Psyllium or plain glucomannan powder delivers the same grams of fibre for less money. It makes little sense as a weight-loss product, because the pooled trials do not show one. And it is not suitable for anyone who has trouble swallowing, has had oesophageal narrowing or bowel obstruction, or tends to take tablets with a sip of water.

Sources and shopping: what to check

Before ordering, decide which dose you will actually take and divide 180 by it. At three capsules a day the bottle lasts two months. At six it lasts one. Budget from that, not from the capsule count.

If you are comparing fibre products, compare grams of fibre per day and cost per gram, not milligrams on the front or bottles per price. Our psyllium powder review and ColonBroom review go through two alternatives: a plain powder and a flavoured psyllium drink.

The Amazon button on this page is an affiliate link. It earns a commission at no extra cost to you and has not moved the 5.8 above. That score is held down by one thing above all: the product's own headline claim is the one its evidence supports least.