Dietary Protein Level Alters Appetite Hormones and Digestive Enzymes in Tilapia | Research

The takeaway

Increasing dietary protein from 30% to 42% in red tilapia reduced growth performance, decreased ghrelin and insulin expression, and increased satiety hormones CCK and peptide YY.

30% protein optimal
Moderate protein diet (30%) produced the best growth while very high protein (42%) reduced growth and altered appetite hormones

What the researchers found

The 30% CP diet optimized growth, while 42% CP decreased ghrelin and insulin expression, increased CCK and peptide YY expression, and reduced growth performance compared to moderate protein levels.

Why it matters

Understanding how dietary protein affects appetite hormones in fish has dual value: optimizing aquaculture feeding and demonstrating conserved peptide hormone mechanisms across vertebrates.

The numbers in context

240 fish; 4 diets (24-42% CP); 42 days; 30% optimal; 42% decreased ghrelin/insulin, increased CCK/PYY

How the study worked

240 red tilapia juveniles across 20 tanks fed four isoenergetic diets (24%, 30%, 36%, 42% crude protein) for 42 days. Measured growth performance, protein retention, body composition, protease activity, and gene expression for digestive enzymes and appetite-regulating hormones.

Who was studied

Juvenile red tilapia (Oreochromis sp.)

What this study cannot tell us

Fish study — appetite regulation mechanisms may not directly apply to human protein intake recommendations. Only one fish species tested. Gene expression measured but not circulating hormone levels.

How to read the evidence

Moderate — well-designed aquaculture experiment with adequate sample size (240 fish) and multiple endpoints, though limited to one species.

When this study was published

Published in 2020; aquaculture nutrition optimization continues to incorporate molecular-level appetite regulation studies.

The bigger picture

The appetite-regulating peptides (ghrelin, CCK, PYY) respond to dietary protein in fish just as they do in mammals, highlighting the ancient evolutionary conservation of these satiety systems.

Questions still open

Is there a similar U-shaped protein response curve for growth in other aquaculture species?
Do these appetite peptide changes in fish inform our understanding of protein-satiety interactions in humans?
What protein digestion products specifically trigger CCK and PYY in the fish gut?

Common questions

Why would too much protein reduce growth in fish?

Excess protein must be metabolized and excreted, which costs energy. The fish also produced more satiety hormones (CCK, PYY) and less appetite-stimulating ghrelin, likely eating less and diverting energy from growth to protein metabolism.

Are fish appetite hormones the same as human ones?

Very similar. Ghrelin stimulates appetite in both fish and humans, while CCK and peptide YY promote satiety. This evolutionary conservation means fish studies can inform our understanding of appetite regulation across species.

Read the original research

Dietary protein modulates digestive enzyme activities and gene expression in red tilapia juveniles.

Animal : an international journal of animal bioscience, 14(9), 1802-1810

View on PubMed ↗Publisher’s paper ↗

Citation

Santos, W M; Costa, L S; López-Olmeda, J F; Costa, N C S; Santos, F A C; Oliveira, C G; Guilherme, H O; Bahiense, R N; Luz, R K; Ribeiro, P A P. (2020). Dietary protein modulates digestive enzyme activities and gene expression in red tilapia juveniles.. Animal : an international journal of animal bioscience, 14(9), 1802-1810. https://doi.org/10.1017/S1751731120000543