Which randomized controlled trials have tested collagen or gelatin supplements for weight loss or body‑composition changes in adults?
Executive summary
Randomized controlled trials (RCTs) testing collagen or gelatin supplements for body‑composition or weight outcomes in adults exist but are relatively few, heterogeneous in population and protocol, and often pair supplementation with resistance training or other interventions (e.g., vitamin C, exercise) rather than testing collagen as a standalone, universal weight‑loss pill [1] [2] [3]. Systematic reviews and individual RCTs report modest reductions in fat mass or preservation/increase in fat‑free mass in some groups — especially older or exercise‑trained adults — but findings are inconsistent and limited by small samples, short durations, and mixed comparators [2] [3].
1. The RCTs that most clearly tested collagen peptides for body‑composition in adults
Key published randomized, double‑blind, placebo‑controlled trials include a 12‑week trial of low‑molecular collagen peptides in overweight/over‑50 adults that reported reductions in body fat after 15 g/day supplementation (designed for adults ≥50 years) [4], and a randomized trial of fish‑skin collagen peptides in overweight adults that followed a 12‑week protocol and measured body composition outcomes [1]. These trials directly measured body fat or body‑composition changes and used placebo controls and randomized allocation [4] [1].
2. Trials pairing collagen with resistance training that changed lean mass or fat mass
Several RCTs combined collagen peptide supplementation with resistance training and reported improvements in body composition and muscle strength, notably the Zdzieblik et al. trial in elderly sarcopenic men and at least one randomized trial in premenopausal women showing improved regional muscle strength and body composition when specific collagen peptides were paired with exercise [1] [2]. Systematic reviews and meta‑analyses focusing on collagen plus exercise conclude that collagen can modestly affect strength and body composition in trained or exercising adults, though effects vary by study design [3] [5].
3. Short‑term gelatin studies that probe collagen synthesis and appetite effects, not long‑term weight loss
Smaller crossover RCTs tested gelatin (often vitamin C–enriched) given before intermittent activity to augment collagen synthesis in tendon/ligament models and monitored biochemical markers rather than sustained weight loss; these trials (e.g., Shaw et al.) document increased markers of collagen synthesis after gelatin but were not designed or powered to detect clinically meaningful changes in body weight [6] [7]. Other short studies examined gelatin’s acute effects on satiety or subsequent energy intake, with mixed results reported in secondary sources [8].
4. What systematic reviews and trial registries reveal about the evidence base
Systematic reviews identify a cluster of RCTs that examine collagen peptides for body composition, often with exercise co‑interventions, and note heterogeneity in peptide source, dose (commonly ~15 g/day), duration (weeks to months), and outcomes (fat mass, fat‑free mass, strength) [2] [3]. Clinical trial registries list additional studies (e.g., NCT03357432) but registry records may lack published results or full methodological detail in public excerpts [9].
5. Limitations, alternative interpretations, and hidden agendas in available reporting
The published trials are limited by small sample sizes, specific populations (older adults, sarcopenic men, exercise programs), varied collagen types and doses, and short follow‑up, which constrain generalizability to broad adult weight‑loss claims [4] [1] [2]. Commercial interest in collagen products creates an implicit agenda to highlight positive outcomes; systematic reviews caution that benefits often appear when collagen is combined with resistance training rather than used alone [2] [3]. Some popular summaries conflate modest fat‑mass changes and improvements in satiety or tissue repair with weight‑loss efficacy for the general population, a leap not fully supported by the RCTs cited [8] [10].
6. Practical synthesis for interpreting the RCT record
The randomized controlled trials that directly tested collagen or gelatin for body composition show some promise — particularly 12‑week collagen‑peptide trials in older or overweight adults and trials combining collagen with resistance training that preserved or increased lean mass and reduced fat mass modestly — but they do not establish collagen as a universal weight‑loss therapy and cannot substitute for larger, longer, independently funded RCTs in diverse adult populations [4] [1] [2] [3]. Where trials exist, the recurring features are 8–12+ week durations, doses around 15 g/day, and better outcomes when collagen accompanies exercise; absence of consistent standalone weight‑loss evidence is the dominant limitation in the literature [3] [2].