What randomized trials have tested gelatin or collagen supplements for weight loss over 6+ months?
Executive summary
A focused review of the provided literature finds randomized human trials of collagen or gelatin for body‑weight or fat‑loss almost all short‑term—typically 8–12 weeks—and no randomized, controlled trials lasting six months or longer are reported in these sources; several 12‑week trials reported modest reductions in fat mass or weight but the evidence is inconsistent and often paired with resistance training or specific formulations [1] [2] [3]. Animal studies and mechanistic data suggest anti‑obesity effects in rodents and appetite‑modulating signals in short human feeding trials, but those cannot substitute for long‑term randomized human trials [4] [5] [6].
1. What the randomized‑trial record actually shows: mostly 12‑week studies
Key randomized, double‑blind, placebo‑controlled human trials cited in these sources ran for around 12 weeks: a trial of low‑molecular collagen peptides in adults ≥50 tested 15 g/day for 12 weeks and reported body‑fat outcomes (Park et al.) [1], and a 2024 Nutrients randomized trial tested a technologically modified collagen (20 g/day via collagen‑enriched bars) for 12 weeks in adults with overweight/obesity and reported greater reductions in weight, BMI, waist circumference and fat mass versus control [2]. Systematic reviews and summaries repeatedly characterize the clinical RCT literature as concentrated in the 8–12 week range rather than long‑term studies [7] [8] [3].
2. Gelatin trials are short and focused on physiology, not long‑term weight loss
The randomized gelatin literature in these sources is even shorter: crossover trials testing vitamin C‑enriched gelatin around exercise interventions measured collagen synthesis over days, not months (one randomized crossover with eight men measured outcomes over 72 hours post‑exercise) [6]. Popular “gelatin trick” narratives rely on acute appetite studies and small feeding experiments that found less hunger or reduced subsequent intake after gelatin in the short term, but those were short‑duration metabolic or feeding studies rather than long randomized trials of sustained weight loss [5] [9].
3. Animal and mechanistic evidence implies potential but doesn’t replace long human RCTs
Preclinical meta‑analyses show several‑week collagen peptide supplementation reduced body mass and improved metabolic markers in rodents on high‑calorie diets, suggesting biological plausibility for anti‑obesity effects [4]. Mechanistic hypotheses include increased gastric swelling, altered postprandial ghrelin or satiety signaling, and the amino‑acid profile of collagen influencing body composition, but those mechanisms remain indirect for the question of sustained human weight loss over six months [2] [5].
4. Evidence gaps, industry framing, and where to look next
None of the provided sources report a randomized, controlled human trial of gelatin or collagen supplements with a duration of six months or longer for weight or fat‑loss; clinical trial registries (for example the trial record NCT03357432) exist but the provided entry here does not summarize a long‑term completed RCT in humans [10]. Several reviews and popular articles note modest short‑term effects but flag inconsistency and limited generalizability, and the marketplace interest in collagen creates a commercial incentive to emphasize positive short RCTs while long‑term evidence remains scarce [7] [9].
5. Bottom line for the question asked
Based on the supplied reporting, randomized trials testing collagen or gelatin for weight loss over six months or more are not documented in these sources; available randomized human trials are predominantly 8–12 weeks and show mixed but sometimes modest reductions in fat mass or weight depending on formulation, dose, and co‑interventions like resistance training [1] [2] [3]. For definitive answers about six‑month outcomes, registered long‑term RCTs and future publications would need to be located or awaited—clinicaltrials.gov and upcoming journal reports are the logical next places to monitor [10].