A single low dose of cod protein hydrolysate before breakfast had no effect on the appetite hormone acylated ghrelin or subjective hunger feelings compared to casein control in 41 healthy adults.
P = 0.991 (no difference)Total ghrelin exposure was virtually identical between cod protein hydrolysate and casein control, showing no acute appetite-modulating effect
What the researchers found
No statistically significant difference was found between cod protein hydrolysate (CPH) and casein control for postprandial acylated ghrelin concentrations (mean difference: 1.05 pg/mL, 95% CI 0.97–1.13, P = 0.266). The total area under the curve for ghrelin was virtually identical: CPH 17,518 pg/mL × min versus control 17,272 pg/mL × min (P = 0.991).
Subjective appetite measures were also unchanged: no differences between CPH and control for satiety (P = 0.794) or fullness (P = 0.996). The results were consistently null across all time points (0, 20, 40, 80, and 180 minutes postprandially).
Why it matters
Bioactive peptides from food protein hydrolysates are widely marketed for metabolic health benefits, but rigorous clinical testing often doesn't support the claims. This well-designed crossover trial shows that at least at a single low dose, cod protein peptides don't affect the hunger hormone ghrelin. This is important for consumers and clinicians evaluating the evidence behind peptide-based nutraceuticals, and it highlights the need for longer-term dosing studies before making health claims.
How the study worked
This was a double-blind, crossover exploratory trial with 41 healthy participants (15 males, 26 females, mean age 51 ± 6 years). Each participant completed two study days separated by 4–7 days washout. On each day, they consumed a test drink containing either 20 mg/kg body weight of cod protein hydrolysate or casein (control) immediately before a standardized breakfast. Acylated ghrelin was measured at baseline and five postprandial time points. Appetite sensations were rated on 100 mm Visual Analog Scales.
What this study cannot tell us
The study tested only a single acute dose, which may be insufficient to affect ghrelin regulation — chronic daily supplementation could produce different results. The dose of 20 mg/kg is relatively low. The casein control is itself a bioactive protein that could mask relative differences. The healthy volunteer population may respond differently than obese or metabolically impaired individuals. The study was self-described as 'explorative,' suggesting it may not have been powered for definitive conclusions.
How to read the evidence
This is a well-designed double-blind, placebo-controlled crossover trial — a strong study design for detecting acute effects. The consistent null results across multiple endpoints and time points suggest a true lack of acute effect rather than a false negative. However, this only addresses single-dose effects and cannot rule out benefits from chronic supplementation.
When this study was published
Published in 2019, this study remains relevant as the bioactive peptide supplement market continues to grow, and well-designed negative trials are essential for evidence-based evaluation of health claims.
The bigger picture
The bioactive peptide supplement market is growing rapidly, with fish protein hydrolysates marketed for weight management, blood pressure reduction, and metabolic health. While some animal studies and in vitro research support these effects, clinical evidence is often weak or negative — as in this trial. Negative results like these are essential for the field's credibility and help refine which doses, durations, and peptide preparations might actually work in humans, guiding future research toward more productive directions.
Questions still open
- Would daily cod protein hydrolysate supplementation over weeks or months produce cumulative effects on ghrelin and appetite regulation?
- Are higher doses of fish protein peptides needed to achieve the metabolic effects seen in some animal studies?
- Would obese or diabetic individuals show different ghrelin responses to bioactive food peptides compared to healthy volunteers?
Common questions
What are bioactive peptides from food and do they really affect appetite?
Why was this a negative result when animal studies showed effects?
Read the original research
Acute effect of a cod protein hydrolysate on postprandial acylated ghrelin concentration and sensations associated with appetite in healthy subjects: a double-blind crossover trial.
Food & nutrition research, 63
Citation
Dale, Hanna Fjeldheim; Jensen, Caroline; Hausken, Trygve; Lied, Einar; Hatlebakk, Jan Gunnar; Brønstad, Ingeborg; Hoff, Dag Arne Lihaug; Lied, Gülen Arslan. (2019). Acute effect of a cod protein hydrolysate on postprandial acylated ghrelin concentration and sensations associated with appetite in healthy subjects: a double-blind crossover trial.. Food & nutrition research, 63. https://doi.org/10.29219/fnr.v63.3507