Konjac Glucomannan, Weight Loss, and Microbiome Health Explained

Obesity seems to be less common in populations that consume large amounts of dietary fibre than in populations that do not. This suggests that increasing the intake of fibres such as glucomannan can help regulate body weight.

In recognition of this correlation, glucomannan is commonly characterised as a weight loss supplement. We’ve compiled some studies to help you better understand glucomannan’s effects on body weight.

Satiety and weight loss

Increased body weight often occurs due to sustained overeating and a lack of physical activity. Glucomannan has been shown to support weight loss through how it regulates hunger and therefore prevents this overeating.

Study: Au-Yeung F, Jovanovski E, Jenkins AL, et al. “The effects of gelled konjac glucomannan fibre on appetite and energy intake in healthy individuals: a randomised cross-over trial” [1]

Glucomannan is a viscous dietary fibre that can form a solid low energy gel when water is added. In gel form, it is an extremely low energy density food (approximately 0·25 kJ/g (0·06 kcal/g). This study investigates whether the low energy properties of glucomannan gels can be used to promote weight loss.

Glucomannan gel shirataki noodles, which are low in energy, were substituted in place of a high-carbohydrate pasta, which are high in energy. The amount of both noodles and pasta were of equal volume. Individuals received preloads that were all 325ml with three different amounts of glucomannan noodle:

all pasta with no glucomannan gel noodle (1849 kJ (442 kcal), 0 glucomannan, control)
half pasta and half glucomannan gel noodle (1084 kJ (259 kcal), 50-glucomannan)
no pasta and all glucomannan gel noodle (322 kJ (77 kcal), 100-glucomannan)

The subsequent food intake as well as the subjective satiety for these individuals was then recorded.

Results

Satiety was assessed over 90 minutes, followed by a dessert. Compared with the control, the total energy intake was:

23 % (−841 kJ (−201 kcal)) lower for 50-glucomannan
47 % (−1761 kJ (−421 kcal)) lower for 100-glucomannan

At 90 minutes, no differences in subsequent food intake was shown for all preloads.

Conclusions

Replacing a high-energy pasta with low-energy glucomannan gel noodles did not promote additional food intake. Even though there was a large energy difference between the two, the intake of low-energy glucomannan did not cause participants to make up for this energy deficit by consuming more food. Therefore, glucomannan caused an overall reduction in total energy intake.

Another feature of glucomannan gel is its high firmness. Since glucomannan is a viscous soluble fibre, consuming it can increase the viscosity of a person’s digestive contents. When digested, glucomannan’s gel-like mass can then delay gastric emptying, the process of food being emptied from the stomach. In this way, it can sustain satiety and prevent the overeating that contributes to excess weight.

Firm fibre gels, such as glucomannan gel, also seem to sustain satiety through the force they exert. A previous study by Marciani et al. [5] used MRI on a variety of agar fibre gels with different strengths. Firm gels greater than 0·65 N exceeded the force that is typically exerted by the stomach during digestion. As a result, these firm gels were retained in the stomach longer. This correlated with a feeling of fullness that provided greater satiety than fibre-gels of a lower strength...

Although the strength of the glucomannan gels in this study were not directly measured, the strength of commercially prepared glucomannan gels have been noted to be between 0·8–1·6 N. Therefore, glucomannan is classified as a firm gel and its strength could help sustain satiety and regulate weight.

Based on present results, it is not clear whether the low energy intake of glucomannan can be continued beyond the subsequent meal. However, it has been shown that reducing energy intake by consuming low energy density foods can be sustained over several days in healthy individuals. A similar effect may be possible through the repeated consumption of fibre gels, but there is not enough available evidence.

The dietary fibres found in fibre gels may also increase the production of SCFAs, short-chain fatty acids, through fermentation by the gut microbiota. This fermentation can influence satiety hormones such as PYY and GLP-1, which influence appetite.

Through its soluble fibre content and very low energy density, glucomannan has been shown to sustain satiety. It is a promising means of preventing overeating and therefore promoting body weight regulation.

Study: Salas-Salvado S, Farres X, Luque X, et al. “Effect of two doses of a mixture of soluble fibres on body weight and metabolic variables in overweight or obese patients: a randomised trial” [4]

This study investigates how consuming a mixture of fibres can affect weight and satiety. The response of body weight was expected to vary, so the study was performed on 200 people. Therefore, this study is one of the few large-scale studies that has analysed the long-term effects of fibre on body weight and satiety.

For 16 weeks, each individual was randomised to receive:

a mixed fibre dose (3g plantago ovata husk and 1g glucomannan) twice daily (b.i.d. group)
or three times daily (t.i.d. group)
or a placebo

Results

Weight loss tended to be higher after both doses of fibre

(24·52 (SD 0·56) and 24·60 (SD 0·55) kg) more than placebo (20·79 (SD 0·58) kg)

Satiety after the meal

increased in both fibre groups compared to the placebo

No significant differences in satiety were observed between the two fibre-supplemented groups (b.i.d. group and t.i.d group).

The weight loss was continuous and constant in the three groups. No weight was regained at the end of the study.

Conclusions

The results of this study suggests that supplementing a weight loss regime with a fibre such as glucomannan could be beneficial. As mentioned in the previous study, fibre does this by promoting satiety and preventing overeating. This study is an affirmation of how glucomannan can regulate hunger and promote weight loss.

Dietary fibres, gut microbiota, and BMI

The human gastrointestinal tract is a thriving environment filled with microbial life. These environments are unique to every individual. An individual’s microbiota first establishes itself at birth. This microbiota can change significantly over the first two to three years of life, and then mostly remain stable throughout adulthood.

Most healthy adult microbiota are dominated by two bacterial phyla: the gram-positive Firmicutes and the gram-negative Bacteroidetes. Several other phyla, including the Actinobacteria, Fusobacteria, and Verrucomicrobia, are also resent at subdominant levels.

Studies have shown that gut microbiota in obese persons are more efficient at recovering energy from resistant dietary components than in lean individuals. Many studies have consistently shown that the ratio of Firmicutes to Bacteroidetes also has an effect on weight. It seems that composition of gut microbiota in those who are obese could be more capable of extracting energy from food and storing that energy as fat.

A diet high in dietary fibres such as glucomannan encourages the presence of healthy gut microbiota such as Bacteroidetes. Therefore, working to remodel the intestinal microbial composition of an individual by promoting healthy bacteria could be a means to regulate weight.

Study: Koliadam A, Syzenko G, Moseiko V, et al. “Association between body mass index and Firmicutes/Bacteroidetes ratio in an adult Ukrainian population” [2]

This study examined the composition of major phyla of gut microbiota in Ukraine adults. It investigated how these compositions differed according to the body mass index (BMI) of an individual. The fecal concentrations of Bacteroidetes, Firmicutes, Actinobacteria and the Firmicutes to Bacteroidetes ratio in 61 individuals were analysed.

Results

The amount of Actinobacteria

was small (5–7%) and comparable in different BMI categories

The amount of Firmicutes

gradually increased with increasing BMI

The amount of Bacteroidetes

gradually decreased with increasing BMI

The Firmicutes to Bacteroidetes ratio also increased with increasing BMI.

This data indicates that obese persons in the Ukraine adult population have a significantly high level of Firmicutes and a low level of Bacteroidetes.

Conclusions

The correlation between a high level of Firmicutes and an increased BMI may occur because Firmicutes are a more effective energy source than Bacteroidetes. As a result, Firmicutes can more efficiently absorb calories. This can lead to subsequent weight gain.

However, there are limitations to this analysis. Main nutrients are known to be absorbed in the small intestine, and only stool samples were investigated in this study. Analysing gut microbiota nearer to the small intestine may produce more accurate data regarding the effects of gut bacteria on body weight.

The dietary habits of certain populations must also be considered, as this can affect the composition of intestinal microbiota. The Ukranian intestinal microbiota composition can be attributed to the consumption of rye bread as well as pork fat, ‘salo’. These two foods are known to be more commonly eaten in Eastern Europe than in Western Europe. Future studies investigating the effect of dietary choices on the composition of intestinal microbiota within a specific population could help provide more accurate data.

Other studies have also produced conflicting results. In some studies, there was a correlation between a high level of Bacteroidetes and an increased BMI in some individuals. However, it is likely that these differences are due to other external influences such as diet, physical activity, as well as social and economic factors. These influences require further research.

The data obtained in this study indicates that obese persons in the Ukraine adult population have a significantly higher level of Firmicutes and lower level of Bacteroidetes compared to normal-weight and lean adults. This suggests that promoting a high level of Bacteroidetes compared to Firmicutes can aid towards weight regulation.

Study: Trompette A, Gollwitzer E, Yadava K, et al. “Gut microbiota metabolism of dietary fibre influences allergic airway disease and hematopoiesis” [5]

This study investigates how dietary fibre, such as glucomannan, can change the composition of gut microbiota. It focuses on how glucomannan can alter the ratio of Firmicutes to Bacteroidetes.

Results

A high-fibre diet

increased the amount of Bacteroidaceae and Bifidobacteriaceae

A low-fibre diet

increased the amount of Firmicutes
particularly those of the Erysipelotrichaceae family, which have also been noted in mice exposed to western high-fat diets

Conclusions

These results suggest that altering the fibre content of an individual’s diet can also affect the composition of their gut microbiota. High fibre diets were high in Bacteroidetes and low fibre diets were high in Firmicutes. This shows that increasing an intake of fibre, such as by consuming glucomannan, can promote a high proportion of Bacteroidetes compared to Firmicutes. As revealed in the previous study, this is the gut microbiota composition of lean and normal-weight individuals. Therefore, glucomannan could supplement weight loss by altering the composition of intestinal microbiota to match that of leaner adults.

Study: Young W, Roy NC, Lee J, et al. “Bowel Microbiota Moderate Host Physiological Responses to Dietary Konjac in Weanling Rats” [8]

This New Zealand study investigated whether adding glucomannan to the diets of weanling rats would affect the composition of their intestinal microbiota.

Groups of conventional or germfree weanling rats were fed

a control diet
diets containing 1.25% konjac
diets containing 2.5% konjac
diets containing 5% konjac

Conventional rats were randomly placed into one of these four groups.

Germ-free rats were assigned to the control or the 5% konjac diet.

The amount of konjac replaced the corresponding amount of corn starch.

Results

After 28 days of feeding konjac, mean body weight gain in conventional or germ-free rats was not significantly affected. There was also no significant difference in food intake between rats in the control group and rats in the konjac groups.

Feeding konjac altered the composition of intestinal microbiota according to how much konjac each group of rats was given. The microbiota of rats in the 5% konjac group were significantly different from those rats in the control group. Rats in the 1.25% konjac group and 2.5% konjac group had less obvious microbiota profiles.

Compared to the control, rats in the 5% konjac group had an increased abundance of

Actinobacteria (4.7% higher)
and Bacteroidetes (2.9% higher)

Plus decreased level of

Firmicutes

The percentage of total intestinal bacteria for rats in the control group or 5% konjac group for 28 days were:

phylum	control group	5% konjac group

Bacteroidetes	15.6%	18.5%
Firmicutes	72.8%	64.6%

Conclusions

These results show that an increased dose of konjac can alter the composition of intestinal microbiota into one that favours Bacteroidetes.

During this study, konjac-induced responses occurred against a setting of numerous developmental changes for the young rats. This suggests that intervening with the composition of intestinal microbiota at a young age through a high-fibre diet can have a continual impact later in life.

Study: Wang H, Hong T, Li N, et al. “Soluble dietary fiber improves energy homeostasis in obese mice by remodeling the gut microbiota” [6]

This study investigated how soluble dietary fiber promotes energy consumption, and therefore weight loss, by advocating an increase of beneficial bacteria.

Eight-week-old mice that had been fed a high-fat diet were randomly grouped to receive

a regular drink (the control group)
2% of soluble dietary fiber Fibersol®-2 (the fibre group)

Body weight was measured weekly. Food intake was measured by calculating the difference in food weight during 24 hour intervals. Energy consumption was examined by measuring oxygen consumption.

At the end of the study, the weight of white adipose tissue, or white fat, was measured. Fecal samples were collected to determine the gut microbiota.

Results

Compared with the control group, at the end of 10 weeks, mice in the fibre group had

reduced weight of white fat
smaller adipocytes, or fat cells
reduced body weight gain

Compared with the control group, mice in the fibre group also had

increased oxygen consumption
increased energy consumption, but not a change in energy intake
decreased ratio of Firmicutes to Bacteroidetes

Food intake did not differ between the two groups. Energy intake was similar for both groups.

Conclusions

Mice in the fibre group had an increased energy consumption, but not a change in energy intake. It seems that soluble dietary fibre can improve energy homeostasis, the control of energy balance. Since increased body weight results from a prolonged energy imbalance, this correction in energy balance can aid in weight regulation.

Obesity also involves the increased expression of lipid metabolism-associated genes. In recognition of this correlation, this study examined the expression of metabolic genes in white fat in diet-induced obese mice. It noted that the expression of key genes involved in lipid storage were suppressed for mice in the fibre group compared to the control. It seems that soluble dietary fibre improves energy homeostasis by regulating these lipid metabolism-associated genes.

The study also found that soluble dietary fibre can restore an intestinal microbiota that has been disrupted by a high-fat diet. A change in diet that promotes growth of Bacteroidetes compared to Firmicutes can cause a shift in microbial composition and promote microbial diversity. This can result in a microbiota which favours more energy consumption and therefore improves energy homeostasis.

This study shows that soluble dietary fiber can promote weight regulation by promoting energy balance.

Article: Wexler AG, Goodman AL. “An insider’s perspective: Bacteroides as a window into the microbiome” [7]

Bacteroides are a genus, or category, within the Bacteroidetes phylum. This article explores how Bacteroides can influence the intestinal microbiota to promote weight regulation and good health.

Bacteroides live and grow exclusively in the gastrointestinal tracts of mammals. This suggests that they are hardy bacteria since they can adapt to the grim environment of the gut. This is because the intestinal tract has many environmental challenges that make sustained colonisation very difficult. One of these challenges is a strong pH gradient from the small intestine to the colon.

Bacteria are most dense in the colon. Here, most of the simple, readily accessible sugars that come from food have already been consumed or absorbed by other microorganisms. Instead, what’s left over are complex long-chain polysaccharides. These polysaccharides are carbohydrate molecules that are derived mainly from plants, such as glucomannan. They are not freely absorbed and cannot be digested by human enzymes.

However, studies have shown that Bacteroides have an unusual ability that allows them to recognise and metabolise certain plant-derived and host-derived polysaccharides. Bacteroides accomplish this through the use of gene clusters. These clusters are called polysaccharide utilisation loci, or PULs for short. A diet rich in plant-derived polysaccharides, such as glucomannan, will lead to an increase of dietary nutrients. In order to use up these increased nutrients, PULs are activated in the gut. Therefore, with increased nutrients, PULs temporarily increase as well.

These polysaccharides can become rare with diets that are low in fibre. When this happens, Bacteroides switch and consume host-derived glycans instead of polysaccharides. Bacteroides can live primarily on host glycans. However, they can also go extinct when they live in the environment of a low-fibre diet over multiple generations.

Therefore, the composition of microbes in the gut are largely dependent on what food and nutrients are consumed. Since bacteria have to compete for shared resources in the gut, it is important to promote the growth of beneficial bacteria such as Bacteroides. This can be done by uptaking plant-derived polysaccharides such as glucomannan.

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References

1. Au-Yeung F, Jovanovski E, Jenkins AL, et al. “The effects of gelled konjac glucomannan fibre on appetite and energy intake in healthy individuals: a randomised cross-over trial”. British Journal of Nutrition Vol. 119 No. 1 (2018): 109-116.

2. Koliadam A, Syzenko G, Moseiko V, et al. “Association between body mass index and Firmicutes/Bacteroidetes ratio in an adult Ukrainian population”. BMC Microbiology Vol. 17 No. 1 (2017): 1-6.

3. Marciani L, Gowland P, Fillery-Travis A, et al. “Assessment of antral grinding of a model solid meal with echo-planar imaging”. The American Journal of Physiology, Vol. 280 No. 5 (2001): G844–G849.

4. Salas-Salvado S, Farres X, Luque X, et al. “Effect of two doses of a mixture of soluble fibres on body weight and metabolic variables in overweight or obese patients: a randomised trial”. British Journal of Nutrition Vol. 99 No. 6 (2008): 1380-1387.

5. Trompette A, Gollwitzer, E., Yadava K., et al. “Gut microbiota metabolism of dietary fibre influences allergic airway disease and hematopoiesis”. Nature Medicine Vol. 20 No. 2 (2014): 159-167.

6. Wang H, Hong T, Li N, et al. “Soluble dietary fiber improves energy homeostasis in obese mice by remodeling the gut microbiota”. Biochemical and Biophysical Research Communications Vol. 498 No. 1 (2018): 146-151.

7. Wexler AG, Goodman AL. “An insider’s perspective: Bacteroides as a window into the microbiome”. Nature Microbiology Vol. 2. No. 5 (2017): 17026.

8. Young W, Roy NC, Lee J, et al. “Bowel Microbiota Moderate Host Physiological Responses to Dietary Konjac in Weanling Rats” in The Journal of Nutrition Vol. 143 No. 7 (2013): 1052-1060.