Across 68 RCTs, protein reduced hunger and increased fullness, with 35 grams as the threshold for triggering significant gut hormone changes (ghrelin ↓, CCK ↑, GLP-1 ↑).
35 gramsminimum protein per meal to trigger significant gut satiety hormone changes including decreased ghrelin and increased GLP-1
What the researchers found
Across 49 acute studies, protein significantly reduced hunger (-7 mm on visual scale, P<0.001), desire to eat (-5 mm, P=0.045), and prospective food consumption (-5 mm, P=0.001). It increased fullness (+10 mm, P<0.001) and satiety (+4 mm, P<0.001).
For gut hormones, protein decreased ghrelin (-20 pg/mL, P<0.001) and increased both cholecystokinin (+30 pg/mL, P<0.001) and GLP-1 (+21 ng/mL, P<0.001). Peptide YY and GIP were not significantly affected.
There was a dose threshold: appetite feelings changed at doses under 35 grams, but the hormonal changes (ghrelin, CCK, GLP-1) only became significant at 35 grams or more. Long-term protein intake showed no consistent effects except a decrease in GLP-1.
Why it matters
Understanding the minimum protein dose needed to trigger hormonal satiety signals is directly useful for designing weight loss diets. The 35-gram threshold for hormone changes gives a practical target for meal planning.
The finding that long-term protein intake does not sustain the same hormonal benefits seen acutely raises important questions about whether the body adapts to high-protein diets over time.
The numbers in context
49 acute + 19 long-term studies; hunger -7mm (P<0.001); fullness +10mm (P<0.001); ghrelin -20 pg/mL; CCK +30 pg/mL; GLP-1 +21 ng/mL; 35g hormone threshold
How the study worked
This was a systematic review and meta-analysis of randomized controlled trials. Researchers included 49 acute and 19 long-term studies involving healthy adults receiving isocaloric meals. They used random-effects models to calculate mean differences and 95% confidence intervals.
Who was studied
Healthy adults (meta-analysis of randomized controlled trials)
What this study cannot tell us
The included studies varied in protein sources, timing, and participant characteristics, which introduces heterogeneity. The distinction between 'acute' and 'long-term' effects depends on study duration, which varied.
The meta-analysis could not determine whether specific protein sources (whey, casein, plant-based) differ in their hormonal effects.
How to read the evidence
Strong evidence from a systematic review and meta-analysis of 68 randomized controlled trials — the highest level of nutritional evidence.
When this study was published
Published in 2020. Protein recommendations continue to be refined by ongoing research.
The bigger picture
The 35-gram protein threshold gives clinicians and dietitians a specific, evidence-based target for meal planning. Understanding that protein triggers satiety hormones (GLP-1, CCK, PYY) at specific doses transforms dietary advice from vague ('eat more protein') to precise.
Questions still open
- Does the protein source (animal vs plant) affect the 35-gram threshold?
- Would combining protein with fiber produce additive hormonal effects?
- Does the 35-gram threshold differ for obese vs lean individuals?
Common questions
How much protein do I need to feel full?
Why does protein reduce hunger more than carbs or fat?
Read the original research
Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials.
Physiology & behavior, 226, 113123
Citation
Kohanmoo, Ali; Faghih, Shiva; Akhlaghi, Masoumeh. (2020). Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials.. Physiology & behavior, 226, 113123. https://doi.org/10.1016/j.physbeh.2020.113123