What randomized controlled trials have tested collagen or gelatin supplements for weight loss and what were their designs and outcomes?
Executive summary
Randomized controlled trials of collagen/gelatin for weight loss are limited but growing: several 12-week RCTs of collagen peptides in older or overweight adults reported modest reductions in body fat, while short-term preload studies with gelatin show increased satiety and lower subsequent calorie intake [1] [2] [3]. Heterogeneity in product type, dose and small sample sizes mean the evidence is suggestive but not definitive [4] [5].
1. Trials reporting reductions in body fat and weight: what was tested and what changed
A 12-week, randomized controlled trial that tested a technologically modified collagen with high swelling capacity enrolled 64 adults with overweight or obesity who consumed two protein bars delivering 20 g of the collagen daily; the collagen group experienced larger decreases in body weight, BMI, waist circumference, fat mass, fatty liver index and systolic blood pressure compared with controls, and no adverse effects were reported in 12 weeks [2]. Independent of that trial, a randomized, double‑blind, placebo‑controlled study of low‑molecular collagen peptides in adults aged 50 and older administered 15 g/day for 12 weeks and reported reductions in total body fat mass versus placebo [1]. Other randomized trials of marine‑ or animal‑derived collagen peptides (for example, a skate-skin peptide study and several peptide + resistance‑training RCTs) have also reported favorable body‑composition changes, but details and effect sizes vary by product and population [6] [1].
2. Short‑term gelatin/preload RCTs: appetite suppression rather than sustained weight loss
Earlier randomized and crossover studies focused on immediate satiety rather than long‑term weight change; a small 2009 trial with 24 volunteers found that a breakfast containing gelatin led to about 20% lower calorie intake at the next meal compared with whey, casein, or soy, and other preload studies reported increased fullness and reduced subsequent intake or a 44% greater hunger suppression for gelatin versus casein in specific protocols [3] [7] [8]. These acute appetite effects explain mechanistic interest but do not by themselves prove durable weight loss, because long‑term maintenance trials have produced mixed results [7] [9].
3. How these RCTs were designed—doses, populations and endpoints
The positive 12‑week trials typically used daily collagen peptide doses in the range of 15–20 g and enrolled older adults or adults with overweight/obesity, with endpoints including body weight, BMI, waist circumference and measured fat mass; many were double‑blind and placebo‑controlled but sample sizes were modest (tens to low hundreds) and interventions ranged from standalone supplementation to supplementation plus resistance training [1] [2] [6]. By contrast, short‑term crossover preload studies used single meals or acute dosing to measure subsequent energy intake and satiety hormones rather than long‑term body‑composition outcomes [3] [10].
4. Limits, heterogeneity and potential funding or publication bias
Interpretation is complicated: supplements differ (native collagen, hydrolyzed collagen peptides, gelatin, gastric‑swelling proprietary complexes), doses vary, trial durations are short for a chronic outcome, and many trials are small—so external validity is limited [11] [2] [1]. Systematic reviewers note that the expanding collagen market has outpaced large RCTs and that study quality and sponsorship can influence outcomes, raising concerns about bias and generalizability [5] [4]. Clinical trial registries list additional trials (e.g., a gelatin/collagen study record on ClinicalTrials.gov), but some records do not report results publicly, underscoring gaps between registered trials and published outcomes [12].
5. Bottom line: modest, context‑dependent signals, not a weight‑loss panacea
Randomized evidence shows consistent short‑term appetite effects for gelatin and several modest body‑fat reductions in 12‑week collagen‑peptide trials—especially in older adults or targeted overweight cohorts using 15–20 g/day—but the literature is heterogeneous, sample sizes are small, and long‑term, large RCTs are lacking, so claims that collagen or gelatin alone produces clinically meaningful sustained weight loss are premature [3] [1] [2] [4]. The most defensible interpretation is that collagen/gelatin can increase fullness acutely and may contribute to small improvements in body composition in some populations when used alongside diet or exercise, but definitive confirmation requires larger, longer, independently funded randomized trials [5] [6].