Semaglutide (Ozempic, Wegovy) vs Glucomannan (Konjac): A Scientific Comparison
By Brian Gaillard
Scientific Summary · Compiled by Brian Gaillard
Brian Gaillard
Hybrid athlete and applied nutrition enthusiast at Nutrition•pro
Ozempic (semaglutide) has become in three years the symbol of a breakthrough in obesity management. Glucomannan, meanwhile, has remained since 2010 the only dietary supplement to have received a European health claim for weight loss. This synthesis brings together 8 pivotal clinical trials and major meta-analyses (NEJM, JAMA, The Lancet, Br J Nutr, Cochrane) covering approximately 25,000 participants, to properly compare two tools that don't aim at the same thing.
Our Approach
This study is neither medical advice nor a recommendation for self-medication. Semaglutide (Ozempic, Wegovy) is a medication subject to strict prescription, indicated for type 2 diabetes and obesity (BMI ≥ 30, or ≥ 27 with comorbidities). Glucomannan is a dietary supplement with modest effects, indicated as an accompaniment to a calorie-restricted diet. No supplement can replace prescribed medical treatment. Nutrition•pro sells glucomannan, not medications: we publish this comparison to clarify the real orders of magnitude, not to designate a winner.
Executive Summary
Raw figures extracted from pivotal trials.
−14.9 %
Weight loss with semaglutide 2.4 mg (68 weeks)
−2.0 %
Weight loss with glucomannan (12 weeks)
~7×
Raw efficacy ratio
~23×
Monthly cost difference
Semaglutide is several times more effective than glucomannan for weight loss: it is a potent medication acting on central GLP-1 receptors. Glucomannan remains well below in raw efficacy, but is used without prescription, without significant adverse effects and at marginal cost. The real question is not "which is most effective?", it is "which is relevant in which clinical context?".
1. Raw Efficacy: GLP-1s Change the Order of Magnitude
Note the durations: 68 to 72 weeks for GLP-1s vs 12 weeks for glucomannan (standard for dietary supplement trials).
Treatment group vs placebo in each pivotal trial. Tirzepatide 15 mg (SURMOUNT-1): −22.5%. Semaglutide 2.4 mg (STEP 1): −14.9%. Liraglutide 3 mg (SCALE): −8.0%. Glucomannan (Onakpoya 2014): −2.0% over 12 weeks. The effect does not amplify significantly beyond this for glucomannan.Semaglutide 2.4 mg produces on average 12.4 kg lost in addition to placebo over 68 weeks (STEP 1). Tirzepatide reaches 17.8 kg. Glucomannan produces 2.1 kg more than placebo over 12 weeks (Onakpoya 2014).
2. Safety: where glucomannan catches up
While semaglutide wins decisively on efficacy, glucomannan wins by a wide margin on tolerability.
GLP-1 analogues cause nausea in 40 to 60% of participants at the beginning of treatment (dose-dependent), and diarrhea in 20 to 30%. Glucomannan can cause bloating and flatulence (5 to 12%) but rarely more. Serious effects (pancreatitis, bowel obstruction, gastroparesis) remain rare but documented for GLP-1s.Percentage of participants who stopped treatment due to adverse effects. Semaglutide 2.4 mg reaches 7% in STEP 1, liraglutide 9.8% in SCALE, compared to less than 1% for glucomannan.
Contraindications to know. GLP-1 analogs are contraindicated in case of personal or family history of medullary thyroid cancer, MEN-2 syndrome, or acute pancreatitis. They require close medical monitoring. Glucomannan has no major contraindications apart from swallowing disorders (risk of esophageal obstruction if taken without water).
3. The cost factor: two different worlds
Semaglutide remains a specialty medication, not reimbursed in France outside official indication (T2 diabetes). Glucomannan costs less than €15 per month.
Wegovy (semaglutide for obesity) costs approximately €280 per month at the pharmacy without reimbursement. Tirzepatide (Zepbound) runs around €320/month. Ozempic (semaglutide for diabetes) is reimbursed for diabetics. Glucomannan sold in pharmacies or drugstores costs €10 to €15 per month.Relative to actual weight loss, semaglutide costs approximately €270 per kilogram of net loss over one year, compared to approximately €60 per kilogram for glucomannan. This measure does not account for sustainability (see following section).
4. Sustainability: the GLP-1 paradox
This is probably the most important nuance in this comparison, and one that is rarely discussed in mainstream media.
The STEP 1 extension study (Rubino et al., JAMA 2022) followed participants 12 months after stopping semaglutide: on average, 2/3 of the weight lost was regained. For tirzepatide, preliminary data suggest a similar pattern. For glucomannan, the question does not arise in the same way: the effect is modest and intake can be prolonged without known risk.
The pharmacological paradox. Semaglutide is extremely effective during treatment, but acts as permanent support: as long as you take it, weight stays low; as soon as you stop, it goes back up. In practice, this means lifelong treatment to maintain weight loss, with a significant cumulative cost (€14,000 over 5 years at current Wegovy pricing). Glucomannan does not cause much weight loss, but integrates into a sustainable eating framework without pharmacological dependence.
5. For whom, in what context
For whom semaglutide is relevant. People suffering from obesity (BMI ≥ 30) or overweight with comorbidities (type 2 diabetes, hypertension, sleep apnea). For these patients, the medical benefit is significant and outweighs the risks. The decision is made with a physician, after evaluating contraindications and with close monitoring.
For whom glucomannan is relevant. People with mild overweight or in ordinary caloric deficit (sports cutting, post-holiday recovery, weight maintenance), who seek to increase satiety to maintain a hypocaloric diet. It is not a solution for severe obesity and cannot substitute for medical treatment when indicated.
What this study does not say. Quality of life, subjective satisfaction, indirect benefits (sleep, energy, inflammatory markers) may differ significantly between the two approaches. And a combination of nutrition + physical activity + psychological support remains the foundation of any sustainable intervention, regardless of the molecule.
Semaglutide is designed for established obesity, not for sports cutting or 4 extra kilos. When the need comes down to increasing satiety during ordinary deficit, glucomannan covers the useful effect for 20 times less cost and without serious side effects.
Brian GaillardHybrid athlete · Author Nutrition•pro
Methodology
This study is a descriptive comparison of pivotal clinical trials and meta-analyses published in peer-reviewed medical journals (NEJM, JAMA, The Lancet, Br J Nutr, Cochrane). The figures presented are extracted directly from the original publications (treatment vs. placebo groups on an intention-to-treat basis).
Important limitations: trial durations differ (56 to 72 weeks for GLP-1s, 4 to 12 weeks for glucomannan). This difference reflects a regulatory and industrial reality: drug trials are designed to demonstrate long-term benefit, those on supplements are rarely funded beyond 12 weeks. The costs mentioned (€280/month for Wegovy) are indicative and vary depending on suppliers and reimbursement status. Indirect comparisons (cross-trial) should be interpreted with caution: the studied populations differ (higher average BMI in GLP-1 trials).
Scientific sources
Wilding JPH et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine, 384:989-1002.
Davies M et al. (2021). Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2). The Lancet, 397:971-984.
Wadden TA et al. (2021). Effect of Subcutaneous Semaglutide vs Placebo as an Adjunct to Intensive Behavioral Therapy (STEP 3). JAMA, 325(14):1403-1413.
Jastreboff AM et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 387:205-216.
Pi-Sunyer X et al. (2015). A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management (SCALE). New England Journal of Medicine, 373:11-22.
Rubino D et al. (2021). Effect of Continued Weekly Subcutaneous Semaglutide on Weight Loss Maintenance (STEP 4). JAMA, 325(14):1414-1425.
Singh G et al. (2022). Efficacy and safety of semaglutide for obesity: systematic review and meta-analysis. Cochrane Database Syst Rev.
Onakpoya I et al. (2014). The use of glucomannan as a weight loss supplement: systematic review and meta-analysis. British Journal of Nutrition, 111(7):1175-1182.
Rondanelli M et al. (2020). The biological effects of glucomannan in patients with overweight or obesity. Nutrients, 12(3):845.
EFSA Panel on Dietetic Products (2010). Scientific Opinion on the substantiation of health claims related to konjac mannan (glucomannan). EFSA Journal, 8(10):1798.
Brian Gaillard
Nutrition and Performance Author
Hybrid athlete for over 10 years: strength training, running, swimming, HIIT, and muay thai. Brian selects, compiles, and contextualizes recent scientific literature on sports nutrition and weight loss for Nutrition•pro editorial content. Each synthesis is based on meta-analyses and clinical trials filtered according to their level of evidence, combined with experience accumulated through his training and exchanges with coaches and nutritionists.
Summary compiled and commented by Brian Gaillard for Nutrition•pro. Reproduction and citation authorized with source attribution.
