What peer‑reviewed trials exist comparing gelatin or collagen supplements to placebo for fat mass reduction?

1. The 2023 low‑molecular collagen peptide trial in adults ≥50: fat loss without added exercise

A randomized, double‑blind, placebo‑controlled trial by Park et al. tested 15 g/day of low‑molecular collagen peptides for 12 weeks in adults aged 50 and older and reported a beneficial effect on total and abdominal fat reduction compared with placebo, despite participants not undergoing resistance training and maintaining usual activity and diet ^[1].

2. Marine (skate) collagen peptide trials showing body‑fat benefits

Multiple reports cite a 2019 randomized, double‑blind, placebo‑controlled trial of low‑molecular collagen peptides derived from skate skin that found greater improvements in body fat measures in the collagen group than placebo over 12 weeks; this marine‑collagen study is referenced across consumer and health summaries ^{[4] [5] [6]}, and the original is listed in reviews and meta‑analyses ^[7].

3. Trials coupling collagen with resistance training—big fat‑free mass gains and larger fat losses

Several well‑cited RCTs combined daily collagen peptide supplementation (commonly 15 g/day) with supervised resistance exercise and observed larger increases in fat‑free mass and greater fat mass reductions in the collagen groups versus placebo, notably the Zdzieblik et al. trial in older sarcopenic men which reported significantly greater gains in FFM and losses of FM with collagen plus training than placebo plus training ^{[2] [8] [9]}.

4. Novel engineered collagen/gelatin formulations with satiating, anti‑obesity effects

A 2024 randomized controlled trial tested a bovine collagen modified to swell and retain water in the stomach (20 g/day) in adults with overweight/obesity and reported larger decreases in body weight, BMI, waist circumference, fat mass and related markers versus control over 12 weeks, an effect the authors link to increased satiation and reduced intake ^{[3] [10]}.

5. Systematic reviews and meta‑analyses — trend toward improved body composition but heterogeneity remains

Systematic reviews note elevated collagen synthesis and some increases in fat‑free mass with 15 g/day collagen peptides, and meta‑analytic signals that collagen plus resistance training can enhance muscle and shift body composition, but reviewers emphasize that collagen’s effect on muscle protein synthesis versus other isonitrogenous proteins is unclear and that trials vary in size, participant age, sex, and outcome measurement ^{[11] [7] [8]}.

6. Limitations, hidden agendas and what the literature does not settle

Across trials the sample sizes are modest, collagen products differ (marine vs bovine vs hydrolyzed peptides vs engineered gelatin), some trials include concurrent resistance training while others do not, and outcome measures (DXA, bioimpedance, body weight) are inconsistent; commercial interests and supplement branding also appear repeatedly in secondary sources and popular summaries, which may amplify positive findings without resolving mechanisms or long‑term effects ^{[12] [9] [13]}.

7. Bottom line for evidence on fat‑mass reduction versus placebo

Peer‑reviewed RCTs exist showing that specific collagen peptide preparations—at doses commonly 15–20 g/day and in some cases engineered gelatin—produce greater fat‑mass reductions or improved body composition than placebo over ~12 weeks, with larger and more consistent effects when paired with resistance training; nevertheless, heterogeneity in formulations, populations, and co‑interventions means the evidence supports cautious optimism rather than a settled clinical recommendation ^{[1] [2] [3] [4] [11]}.