Effects of konjaku products on weight loss and gut microbiota in people with obesity Original paper

Konjaku (also known as konjac or konnyaku) is made from the edible root corm of a subtropical Asian plant. The corm, which has been used as food in Asia for centuries, has a very high proportion of glucomannan, a non-human-digestible soluble fiber that swells in water, and in the presence of alkali, it forms a strong, thermostable gel.^[1] This konjac gel can be shaped into noodles ("shirataki"), rice, slabs, and other forms, which are composed mostly of water and thus are suitable for people following ketogenic, low-carb, gluten-free, vegan, and calorie-restricted diets.

Konjac is also taken as a dietary supplement for weight loss,^[2][3] to lower cholesterol levels,^[4] and to help with constipation.^[5] This study examined konjac not only as a weight loss supplement, but also as a potential cause of changes to the intestinal microbiome.

This randomized controlled trial recruited 78 men and women (ages 25–35) with BMI ≥ 28 (the WHO criteria for obesity is BMI ≥ 30) who were dieting on their own initiative by controlling their food intake. The participants were randomized to take either 5 grams of konjac flour or 5 grams of a lotus root starch placebo plus 150 mL of water twice daily in a divided dose (before breakfast and dinner) for 5 weeks.

The researchers collected anthropometric (body) measurements (weight, BMI, fat mass, body fat percentage [BF%], waist-to-hip ratio) and blood and stool samples at weeks 0 and 5.

The blood samples were analyzed for fasting blood glucose, cholesterols (total cholesterols, HDL-C, HDL-C), glycated hemoglobin (HbA1c), triglycerides, aspartate aminotransferase (AST; a marker of liver function), and alanine aminotransferase (ALT; a marker of liver function). The stool samples were analyzed for bacterial diversity and microbial composition.

Overall, 12% of the participants dropped out, mostly due to antibiotic use. Among the remaining 69 participants, there were no significant changes in the placebo group for weight or fat mass, but BMI and fat mass both decreased significantly in the konjac group (BMI by an average of 1.4 and fat mass by an average of 2.8 lbs). In the konjac group, the average %BF decreased by 1.9%, HbA1c decreased by 0.17%, triglycerides by 0.39 mmol/L, AST by 3.2 U/L, and ALT by 5.8 U/L.

The stool samples from the konjac group had greater bacterial alpha diversity (i.e., more different species) after 5 weeks compared to baseline, whereas the placebo group's stool samples had lower bacterial diversity at the end of the study compared to baseline. The konjac group's stool samples had significantly higher proportions of bacteria in the phyla Actinobacteria and Acidobacteria after 5 weeks. Significant changes were also noted in specific families and genera of bacteria, some of which have been positively or negatively associated with obesity in other studies.