Glucomannan for Weight Loss

Last updated July 10th 2015

Glucomannan is a fibrous ingredient that is thought to suppress the appetite. Clinical studies have suggested that it can reduce cholesterol levels, but results regarding weight loss are mixed.

Gulcomannan is a type of fibre that is sometimes added to weight loss supplements; it is thought to work primarily as an appetite suppressant, targeting two different methods of curbing the appetite.

Unlike most weight loss supplement ingredients, glucomannan has been the subject of a number of clinical studies. Results of these studies are mixed, but it seems that the ingredient could have a slight impact on weight loss and related factors, such as blood glucose and cholesterol levels.

The ingredient has been associated with some side effects and is not suitable for everybody. People with diabetes should consult a doctor before consuming glucomannan.

What is Glucomannan?

Glucomannan is a type of sugar that is derived from a plant source. The most commonly used source is the konjac plant (Amorphophallus konjac), where it is said to make up 40% of the dry weight of the plants’ roots. The konjac plant is native to subtropical and tropical parts of Asia and its root is commonly used as food in these areas. Besides konjac, glucomannan can also be obtained from corm or salep.

The ingredient is often used as a thickener or gelling agent in foods and has long been used as an ingredient in traditional medicines; it is said to have the potential to help treat a range of health conditions. Glucomannan is available in capsule, powder or tablet form and is typically used for the treatment of constipation and diabetes. Although there is a lack of evidence in support of these claims, glucomannan is also sometimes used to treat cancer and atopic diseases, and is thought by some to be a prebiotic.

The substance is thought to be able to help with the control of blood sugar levels and to reduce cholesterol levels. It is also regularly added to weight loss supplements; precisely how it is believed to help with weight loss will be discussed in more detail in the ‘How Does Glucomannan Work?’ section below.

To date, no products containing glucomannan have been approved by the Food and Drug Administration (FDA) that are being advertised as treatments for any of the aforementioned health conditions, though some have been authorised for weight management, appetite suppression, constipation, and high cholesterol in Canada.

How Does Glucomannan Work?

Glucomannon is available to buy as a supplement on its own from health stores or as an ingredient in a great number of different weight loss products. It is claimed to help to boost weight loss through its appetite suppressing qualities. Different appetite suppressants can work in several different ways.

The majority of appetite suppressing weight loss supplements and ingredients are claimed to work by changing the concentrations of certain neurotransmitters in the brain. Neurotransmitters are chemical signals, some of which are involved in the control of appetite (such as norepinephrine and serotonin). By changing the amounts of these substances in different parts of the brain, some ingredients are thought to have the potential to make the brain signal to the body that it is not hungry.

Unlike most ingredients that are touted for having appetite suppressing effects, glucomannan is not claimed to work in this way. Instead, it is said to target two different methods of appetite suppression.

Firstly, it is believed to physically fill the digestive tract, making a person feel full for longer. This is because glucomannan is a type of soluble fibre; as such, when it comes into contact with water in the gastro-intestinal tract, it is thought to swell and bulk up to form a gel-like substance. This is sometimes believed to slow the digestion of foods and remain in the stomach for longer than other foods normally would.

Glucomannan is also thought to slow down the rate at which sugars and carbohydrates are absorbed through the gut, which in turn may help to control blood glucose levels; this is the second mechanism through which the ingredient is thought to aid appetite suppression.

After a person consumes a meal or a snack, the sugars are absorbed into the bloodstream causing a significant spike in blood glucose levels. This is known as the ‘postprandial blood glucose spike’. Insulin is a hormone that is secreted by the pancreas; its main job in the body is to control levels of blood glucose. Carbohydrates are broken down to form sugar molecules, which are then either stored or converted to energy; it is the job of insulin to distribute the glucose molecules around the body. As such, a spike in glucose levels causes a spike in insulin levels since the hormone will be released to control the sugars.

It is important that blood glucose and insulin levels remain stable and under control. In people with diabetes, the body does not produce enough insulin to reduce the blood glucose spike that occurs after meals. This can lead to hunger. If on the other hand, lots of insulin is released to act on the blood glucose, a dip in glucose levels can be experienced. This dip in blood sugar is thought to result in hunger cravings for sugary foods, particularly after the consumption of foods high in carbohydrates.

Through both of these methods (physically filling the stomach and altering blood glucose levels) glucomannan is claimed to have the potential to prevent snacking and also to keep you feeling fuller for longer after a meal. In turn, your calorie intake should be reduced and you should lose weight. The ingredient may also be useful for individuals who are trying to stick to a portion-controlled diet. Whether or not glucomannan actually has the potential to work in these ways will be discussed in the ‘Clinical Studies’ section below.

Glucomannan Clinical Studies

Unlike many ingredients that are common to weight loss supplements, glucomannan has been the subject of numerous clinical studies. Trials have been undertaken to determine both the effects of glucomannan on weight loss directly and on related factors, including blood glucose and lipid levels. A selection of these studies will be summarised below.

Clinical studies provide evidence of the effects and safety of a substance. In terms of weight loss, these studies generally investigate whether or not a product or ingredient has the potential to increase fat loss and improve BMI, and whether or not it is able to achieve this safely. The most reliable of these studies are performed using human subjects using randomised, double blind, placebo controlled methods, though some preliminary studies may be undertaken in vitro or using animal subjects.

In one clinical study, two groups of 25 severely obese individuals were subjected to three months of a reduced-calorie diet. One of the groups was given a 4g glucomannan-based dietary supplement whilst the other was not given any form of supplementation. By the end of this trial, the individuals in the glucomannan group had lost significantly more weight in relation to fatty mass than the control group, and they better adhered to the diet. No adverse side effects were reported. It should be noted however, that 50 subjects is quite a small sample size and so these results cannot be deemed conclusive.

One of the first clinical studies on glucomannan for weight loss was published in the International Journal of Obesity in 1984. This trial involved a total of 20 subjects, all of whom were obese. Using double blind methods, the participants were divided into two groups. The first group was given two 500mg capsules of glucomannan fibre twice a day whilst the second group was given a placebo at the same dosage. The treatments were taken with 8oz of water one hour before each of the three meals a day. The participants were not told to alter their diet or exercise patterns. After eight weeks, measurements were taken and participants in the glucomannan group were seen to have lost significantly more weight than those in the control group; a reduction in serum cholesterol and LDL cholesterol was also noted with the consumption of glucomannan.

A third study was undertaken, this time using children as subjects. Twenty-three participants were involved, all of whom were obese; the subjects were aged between 5 and 18 and were all obese. The subjects were divided into two groups, the first of which received 2-3 caps of glucomannan fibres twice daily and the second of which received a placebo. They were all provided with a balanced diet. The results of this study showed that excess weight and triglyceride levels were significantly reduced in children who had been taking the glucomannan for four months, as were cholesterol levels. The authors did not note any adverse side effects.

Another study was undertaken using a sample of children under the age of 15 since glucomannan is commonly used in the treatment of paediatric obesity. A total of 60 participants took part and were divided equally into a glucomannan group and a placebo group. Methods were double blind and placebo controlled; half of the participants consumed 1g glucomannan twice a day for a period of two months whilst the other half consumed a placebo. The volunteers all followed a normocaloric diet which was evaluated every two weeks. By the end of the two months, both groups had lost significant amounts of weight, but the difference in weight lost between the two groups was not significant.

The results of this study were also not positive. The trial was performed in an attempt to investigate the impacts of glucomannan on weight loss. A total of 56 volunteers took part in the trial. They were divided into two groups, the first of which consumed 1.33g glucomannan one hour before breakfast, lunch and dinner each day with 8oz water, and the second of which took a placebo under the same conditions. The trial lasted for eight weeks and measurements were taken at the end. The results of this study showed no significant difference in weight loss or any of the other relevant factors (including fullness and blood glucose and lipid levels) between the two groups, although the glucomannan did appear to be well-tolerated by subjects.

Several review studies have also been published. One meta-analysis was published in 2008; the authors of this study attempted to quantify the effects of glucomannan on a number of obesity-related factors, including blood glucose levels, body weight and plasma lipids. They gathered data from fourteen published scientific studies that used randomised, placebo controlled methods. By pooling the data and performing statistical analyses on them, the authors found that glucomannan has a significant effect on lowering total cholesterol, LDL cholesterol, body weight, and triglyceride levels, though it did not appear to have a significant impact on HDL cholesterol or blood pressure.

Another review study, published in 2005, summarised clinical studies on glucomannan for weight loss to date. They found that the consumption of 2-4g of glucomannan per day appeared to be well-tolerated and also caused significant weight loss in overweight and obese participants. The authors also noted that some evidence indicates that glucomannan may have a beneficial impact on weight loss due to its satiety-promoting effects and because it causes an increase in faecal energy loss. It was also concluded that the ingredient has been shown to benefit lipid and lipoprotein levels.

Finally, a number of studies have been performed on the effects of glucomannan on blood glucose levels. One study, for example, specifically investigated the effects of glucomannan on carbohydrate absorption and the postprandial insulin response by looking at results from other studies to date. The author wrote that the consumption of 4-5g of glucomannan with meals in fluid or mixed with food has the potential to slow the absorption of carbohydrates and so reduce the postprandial insulin spike by up to half. Moreover, it is noted that the substance can increase satiety and weight loss as well as reduce LDL cholesterol levels, improve blood glucose control and treat constipation without adverse side effects.

Glucomannan Side Effects

Whilst most of the clinical studies described above did not note any adverse side effects that were the result of glucomannan consumption, some potential side effects have been reported. It is important that you read the instructions that come with the specific product you are considering taking, and consult a doctor if you are unsure. If you suffer from any severe or prolonged side effects, it is recommended that you stop taking the product and consult a doctor.

According to WebMD, the safety of glucomannan depends on the form that you are consuming. It is stated that in powder or flour form, the type that is found in foods, it is likely to be safe for consumption. In powder or capsule form as taken in medicinal amounts, glucomannan may be safe for adults and children for up to four months, whilst solid tablets are said to be possibly safe for adults but likely to be unsafe for consumption by children. It is not recommended that children consume weight loss supplements in general, as well as glucomannan alone.

The most common concern regarding glucomannan is that it can cause blockages of the throat or intestines. Several cases of oesophageal blockages have been reported in people who have been taking glucomannan for the purpose of weight loss. One scientific paper described seven cases of oesophageal blockages, five of which were complete blockages and four of which were caused by the consumption of a single tablet. In order to avoid this potentially dangerous effect, it is recommended that if you are consuming glucomannan, you make sure that you take it with plenty of water and stay hydrated throughout the day.

As discussed in the clinical studies section, is also possible that glucomannan can alter blood glucose levels; as such, it should be avoided by those who have low blood glucose and precautions should be taken if you have been diagnosed with diabetes. states that glucomannan has been shown to be safe in dosages of up to 13g per day. The website also notes some more mild side effects such as diarrhoea, stomach cramps, flatulence and bloating. It has also supposedly been linked with cases of occupational asthma and cholestatic hepatitis (drug-induced liver disease), though these have not been conclusively attributed to the intake of glucomannan.

Is there anybody who shouldn’t take Glucomannan?

Clinical studies have indicated that the consumption of glucomannan can significantly alter blood glucose levels. This may be beneficial for individuals who suffer from type II diabetes, but it is important that if you have diabetes and are considering taking glucomannan you consult a doctor and ensure that it is suitable for you. You should also continue to monitor your blood glucose levels carefully for the duration of time that you are taking glucomannan and alter any medications that you are taking in accordance with any changes.

For the same reason, it is recommended that you avoid glucomannan if you have scheduled surgery in the next two weeks. You should also not take glucomannan in the two weeks after surgery.

Due to a lack of clinical studies, it is not advised that pregnant or breastfeeding individuals consume glucomannan. This is simply because not enough information is available, so it is not known whether the substance may cause problems.

Finally, if you are taking any form of medication by mouth, you should consult a doctor before taking glucomannan. This is because the ingredient is believed to absorb substances in the gastro-intestinal tract (including the stomach). As such, the glucomannan could reduce the amount of the medicine that your body can absorb, thus decreasing its effectiveness. It is though that this can be avoided by consuming glucomannan an hour or more after you have taken any oral medications.


Glucomannan is claimed to target appetite suppression through two different methods. Some clinical studies have indicated that it may have the potential to suppress the appetite and alter blood glucose levels, thus aiding weight loss. However, the results of clinical studies have not been entirely consistent, and other studies suggest that the ingredient will not have any significant effect on weight loss. There are gastro-intestinal side effects associated with the ingredient as well as a risk of throat and intestinal blockages if it is not consumed with enough water. The ingredient is fairly easy to get hold of, but is not suitable for everybody.