What the research suggests

Weight loss and appetite: uncertain to small at best

• A well-designed 8-week placebo-controlled trial used 1.33 g before each meal, 3.99 g/day total, with 8 oz (about 240 mL) water. It found no difference from placebo in weight loss, hunger/fullness, body composition, glucose, or lipids. Temporary belching, bloating, and fullness were more common with glucomannan. See Keithley et al. (2013).
• A 2014 meta-analysis of randomized trials similarly found no statistically significant weight-loss benefit: Onakpoya et al..
• A small 2023 randomized trial of 250 mg konjac glucomannan twice daily in gummies reported less hunger and a smaller waist circumference over 14 days. It is interesting for a low-dose approach, but it was short and small, so it cannot establish meaningful or durable weight loss. Fernandes et al. (2023), PMID 36435474.
• A 2024 placebo-controlled trial found substantial weight loss, but the supplement was a combination of glucomannan, inulin, and psyllium, in people with obesity and selected gene variants. It therefore does not show that glucomannan tablets alone caused the result. GI side effects occurred in 74.6% of the combination-fiber group. Pokushalov et al. (2024), PMID 38398881.

Cholesterol: the best-supported potential benefit

• Musazadeh Vali et al. (2024), PMID 39385065 found lower total cholesterol, LDL-C, and apolipoprotein B, but the included studies were highly heterogeneous.
• Zhu et al. (2025), PMID 39528010 also found statistical reductions in total and LDL cholesterol, while concluding that the size of the reduction was not clinically important and that glucomannan should be considered, at most, an adjunct for dyslipidemia.

Blood sugar: possible benefit, mainly if diabetes is present

• A 2022 meta-analysis of six small trials found lower fasting glucose, but not a statistically significant reduction in post-meal glucose. Mirzababaei et al. (2022), PMID 35673426.
• A 2023 meta-analysis in type 2 diabetes found improvements in fasting glucose, 2-hour post-meal glucose, fasting insulin, total cholesterol, and LDL. However, it included only six trials, so the confidence in the exact size of benefit is limited. Zhang et al. (2023), PMID 36771306.

Pros and cons

How I would approach a cautious self-trial

1. Use only a reputable product whose label gives clear water instructions. “One tablet” is not a meaningful universal dose because tablet strengths vary widely.
2. Take it with at least a full glass of water, and do not take it dry, with only a sip, or immediately before lying down.
3. If your goal is meal fullness, take it before the meal only if the product label supports that timing. The negative 2013 trial used it one hour before meals, so pre-meal timing does not guarantee benefit.
4. Keep other oral medicines separated by at least 2 hours as a prudent default. Glucomannan may delay or reduce drug absorption. A gastroenterology reference lists it as a bulk laxative and warns of delayed absorption of other medications and obstruction risk. Sleisenger and Fordtran's Gastrointestinal and Liver Disease, p. 2707.
5. Stop and seek urgent care for trouble swallowing, chest/throat pain after swallowing, persistent vomiting, or severe abdominal pain/distension.

Do not start without clinician or pharmacist input if you have

• Trouble swallowing, prior food impaction, esophageal narrowing, severe reflux with swallowing symptoms, gastroparesis, or a bowel narrowing/obstruction history
• Diabetes treated with medication, especially insulin or sulfonylureas
• A medication where timing and absorption are especially important, such as thyroid replacement, anticoagulants, seizure medicines, or oral contraceptives
• Pregnancy or breastfeeding, because supplement-specific safety evidence is limited