A 12-week trial in 73 obese adults found whey protein reduced subjective hunger and increased peptide YY response, but did not improve GLP-1, insulin sensitivity, body composition, or blood pressure.
Hunger reduced, metabolism unchangedWhey protein lowered subjective hunger (p=0.02) and boosted PYY, but produced no measurable changes in insulin sensitivity, body composition, or metabolic rate over 12 weeks
What the researchers found
Whey protein for 12 weeks reduced subjective hunger (p=0.02) and increased postprandial peptide YY response (with low fiber), but had no effect on insulin sensitivity, GLP-1, body composition, 24-hour blood pressure, or energy expenditure versus maltodextrin control.
Why it matters
Whey protein is widely promoted for weight management, but this rigorous trial shows its benefits may be limited to appetite reduction without meaningful metabolic improvements — important context for consumers spending money on protein supplements.
The numbers in context
73 randomized; 60 g/day WP; 12 weeks; hunger p=0.02; PYY increased with WP+LoFi; no effects on GLP-1, GLP-2, GIP, insulin sensitivity, body composition, BP, or energy expenditure
How the study worked
12-week, double-blind, randomized, controlled, parallel study. 73 subjects with abdominal obesity. 4 groups: whey protein hydrolysate (60g/day) or maltodextrin + high-fiber (30g/day) or low-fiber (10g/day). Assessed: insulin sensitivity, gut hormones (GLP-1, GLP-2, GIP, PYY), body composition, blood pressure, energy expenditure.
Who was studied
Adults with abdominal obesity
What this study cannot tell us
Relatively small study (73 subjects, 65 completed). 12-week duration may be insufficient for body composition changes. 60g/day whey protein is a high dose. Maltodextrin control may have metabolic effects of its own. Population-specific (abdominal obesity).
How to read the evidence
Moderate evidence: double-blind RCT design, but relatively small sample (73) and short duration (12 weeks) limit power to detect modest metabolic changes.
When this study was published
Published 2021. The appetite-hormone effects of dietary protein continue to be studied, with growing interest in how protein quality affects GLP-1 and PYY responses.
The bigger picture
This study tempers expectations about whey protein as a metabolic fix. While appetite-suppressing effects (via peptide YY) are real, they don't automatically translate to weight loss or metabolic improvement — highlighting the complexity of obesity treatment beyond simple hunger control.
Questions still open
- Would longer whey protein supplementation eventually produce body composition changes?
- Does the hunger reduction from whey protein lead to reduced calorie intake and weight loss over time?
- Would whey protein combined with exercise produce different metabolic results?
Common questions
Does whey protein help with weight loss?
Does whey protein affect GLP-1 levels?
Read the original research
Effects of whey protein and dietary fiber intake on insulin sensitivity, body composition, energy expenditure, blood pressure, and appetite in subjects with abdominal obesity.
European journal of clinical nutrition, 75(4), 611-619
Citation
Fuglsang-Nielsen, Rasmus; Rakvaag, Elin; Langdahl, Bente; Knudsen, Knud Erik Bach; Hartmann, Bolette; Holst, Jens Juul; Hermansen, Kjeld; Gregersen, Søren. (2021). Effects of whey protein and dietary fiber intake on insulin sensitivity, body composition, energy expenditure, blood pressure, and appetite in subjects with abdominal obesity.. European journal of clinical nutrition, 75(4), 611-619. https://doi.org/10.1038/s41430-020-00759-4