What randomized controlled trials compare gelatin or collagen supplements directly with whey or casein for short‑term appetite and energy intake?
Executive summary
Randomized controlled trials directly comparing gelatin or collagen with whey or casein for short‑term appetite and energy intake are limited but informative: a 2009 randomized breakfast study found gelatin (and α‑lactalbumin) lowered subsequent lunch energy intake relative to whey and casein (about a 20% reduction) [1] [2], a 36‑hour single‑protein diet trial reported greater appetite suppression on gelatin versus casein [3], while small acute crossover trials—most notably a 2022 pilot—found no change in subjective appetite or ad libitum intake after a single 40 g dose of hydrolysed collagen versus whey despite hormonal differences [4] [5].
1. Acute breakfast comparison: gelatin lowered lunch intake versus whey and casein in a randomized crossover
A randomized, single‑blind crossover study that served custard breakfasts spiked with different proteins (casein, soy, whey, whey‑GMP, α‑lactalbumin, gelatin, gelatin+tryptophan) to 24 healthy adults reported that breakfasts containing α‑lactalbumin or gelatin reduced appetite ratings by ~40% and produced an approximately 20% lower energy intake at an ad libitum lunch three hours later compared with breakfasts containing casein or whey [1] [2], an outcome the authors tied statistically to appetite ratings (R2 = 0.4, p < 0.001) [1].
2. Short‑term (36 h) controlled diets: gelatin suppresses appetite compared with casein
In a tightly controlled randomized comparison of single‑protein diets over 36 hours, researchers found that gelatin—an incomplete protein—produced greater appetite suppression than the complete protein casein, while energy expenditure was similar between diets; the authors suggested this could translate to reduced energy intake if sustained, but emphasized the short duration and metabolic tradeoffs of an incomplete amino‑acid profile [3].
3. Single‑dose hydrolysed collagen vs whey: small crossover pilots show hormonal signals without intake changes
A double‑blind, randomized crossover pilot with 10 healthy women that administered a single 40 g dose of hydrolysed collagen or whey found higher leptin at 60 minutes after collagen but no differences in subjective hunger, desire to eat, fullness (VAS) or subsequent energy consumption—demonstrating that acute hormonal changes do not always translate to short‑term intake differences in small samples [4] [5].
4. Longer and larger randomized trials give mixed context but not clear short‑term consensus
Larger or longer randomized studies help contextualize but do not resolve short‑term appetite questions: trials comparing whey and casein show dose‑ and timing‑dependent effects (e.g., whey reduced hunger at lower protein energy percent but not at higher doses) [6], and a randomized 8‑week double‑blind trial in overweight women compared daily whey versus hydrolysed collagen supplementation and examined intake, adiposity and biomarkers—useful for chronic effects but not strictly short‑term postprandial appetite responses [7]. Systematic and single‑protein trials also report heterogeneity by dose, amino‑acid composition and study design [8] [9].
5. Reading the evidence: converging signals, important gaps and practical limits
Collectively these randomized trials suggest a credible signal that gelatin (or gelatin‑like hydrolysed collagen) can be as or more satiating than some complete milk proteins in certain short‑term experimental setups—especially in controlled meals where gelatin reduced subsequent intake [1] [3]—but the evidence is heterogeneous: small sample sizes, single doses, differing protein doses and forms (gelatin vs hydrolysed collagen vs intact whey/casein), short windows (single meal or 36 h) and inconsistent translation from hormonal changes to actual intake [4] [6] [7]. Important unanswered questions remain about dose‑response, real‑world meal contexts, sex, age, body‑composition effects and whether observed short‑term appetite suppression with gelatin persists or translates to meaningful long‑term energy intake and body‑weight changes; existing RCTs cited here provide partial but not definitive answers [1] [4] [3] [7].