Konjac (Amorphophallus konjac), primarily in the form of glucomannan, is supported by scientific evidence for its use in managing components of metabolic syndrome. Glucomannan is a water-soluble dietary fiber derived from the konjac plant, and its primary mechanism involves increasing satiety, delaying gastric emptying, and reducing the absorption of cholesterol and glucose.

Several randomized controlled trials and meta-analyses have demonstrated that konjac glucomannan supplementation can modestly reduce body weight, fasting blood glucose, LDL cholesterol, and total cholesterol, as well as improve other metabolic parameters related to metabolic syndrome. For example, a 2008 meta-analysis published in the American Journal of Clinical Nutrition reported significant reductions in total cholesterol, LDL cholesterol, triglycerides, and body weight with glucomannan supplementation in both healthy and hyperlipidemic subjects. Another systematic review (2017, Obesity Medicine) found beneficial effects on fasting blood glucose and body weight, though the magnitude of the effects was generally modest.

While the evidence is not overwhelmingly strong (hence a rating of 3), it is consistent enough to suggest that konjac serves as a useful adjunct for improving metabolic parameters. The European Food Safety Authority (EFSA) has also approved health claims for glucomannan's role in the reduction of blood cholesterol and maintenance of normal blood cholesterol levels.