Weight & Metabolic
Why Am I Still Hungry on a GLP-1?
The short answer
In controlled feeding trials, semaglutide cut how much food people ate at a free-choice meal by roughly 35-39% compared with placebo, and reduced self-reported hunger significantly. But the effect is not uniform: about 1 in 10 participants in obesity trials lost less than 5% of body weight, and the mechanism most people assume explains appetite loss — a slowed stomach — accounted for only 4-6% of the variation researchers could measure. No trial has identified in advance who will keep feeling hungry.
Quick answers
- What is it?
- This examines why some people on semaglutide or tirzepatide don't experience the strong appetite suppression the drugs are known for, and what actually drives the appetite-reducing effect in those who do.
- Why are people interested in it?
- Roughly 1 in 10 people on these drugs lose less than 5% of body weight, and people want to understand why the appetite effect isn't uniform.
- What has actually been studied?
- Controlled feeding trials measuring food intake at free-choice meals in people on injectable and oral semaglutide, studies directly measuring gastric emptying alongside appetite, and a 2026 narrative review searching for predictors of GLP-1 response.
- How strong is the evidence?
- Solid on the average effect, weak on individual prediction: controlled feeding trials consistently show semaglutide cut food intake by roughly 35-39% on average, but gastric emptying — the mechanism people usually assume — explained only 4-6% of the variation, and no baseline test currently predicts who won't respond.
- What don't we know yet?
- What actually drives the appetite effect if not the stomach, who will be a low- or non-responder before treatment starts, whether appetite suppression fades over time on stable dosing, and whether tirzepatide's appetite mechanism matches semaglutide's.
- Where can I read the original research?
- Sources at the bottom of this page: Friedrichsen M, Breitschaft A, Tadayon S, Wizert A, Skovgaard D, Diabetes, Obesity and Metabolism, 2021; and Gabe MBN, Breitschaft A, Knop FK, et al., Diabetes, Obesity and Metabolism, 2024.
The short answer: Across several controlled feeding studies, semaglutide reduced how much food people ate at a free-choice meal by roughly 35-39% compared with placebo, and it reduced self-reported hunger while increasing fullness and satiety. That is a large average effect. But it is an average — about 1 in 10 people in controlled obesity trials lost less than 5% of their body weight, and researchers have found that the mechanism most people assume is doing the work, a slowed stomach, explains only a small fraction of why appetite drops. Nobody has yet identified who will still feel hungry before they start treatment.
What the research shows
Appetite drops sharply, on average
Several trials measured appetite directly rather than just tracking the scale. In a 20-week trial of once-weekly subcutaneous semaglutide 2.4 mg in 72 adults with obesity, participants ate 35% less at an ad libitum lunch than the placebo group — 1,736 kJ versus 2,676 kJ, a difference of 940 kJ (P<0.0001). They also reported less hunger, more fullness, more satiety, and fewer food cravings on validated questionnaires (P<0.02 for all). Body weight fell 9.9% with semaglutide versus 0.4% with placebo.
A separate 20-week trial of once-daily oral semaglutide 50 mg in 61 adults found a similar pattern: energy intake at an ad libitum lunch fell by 39.2 percentage points relative to placebo (95% CI, -59.0 to -19.4), alongside a 9.8% weight reduction. A third, smaller crossover trial in 15 people with type 2 diabetes found oral semaglutide cut daily energy intake by 38.9% relative to placebo (estimated treatment difference -5,096 kJ; P=0.0001). A narrative review of tirzepatide trials similarly reported reduced food intake and lower overall appetite scores, though it did not report the same kind of controlled meal-test figures.
The stomach isn't doing most of the work
The obvious explanation is that these drugs slow gastric emptying, so food sits in the stomach longer and people feel full sooner. The data don't support that as the main driver. In the 72-person semaglutide trial above, the researchers measured gastric emptying directly (via paracetamol absorption) and found only an 8% change that became statistically non-significant once adjusted for body weight — "no evidence of delayed gastric emptying" by week 20. The oral semaglutide trial found the same thing: no measurable difference in gastric emptying at week 20 despite a 39% drop in energy intake.
A 2026 secondary analysis of a 16-week randomized liraglutide trial (40 participants) went further and tested the relationship directly. Gastric emptying speed accounted for only 4-6% of the variance in appetite measures across the full cohort, and within the liraglutide-treated group alone there was no significant correlation at all. People whose gastric emptying stayed normal reported the same appetite suppression as people whose emptying was persistently or transiently delayed. The authors concluded that delayed gastric emptying "appears to play little direct role in appetite suppression induced by liraglutide." A separate trial comparing short-acting lixisenatide with long-acting liraglutide in 50 people with type 2 diabetes reached the same conclusion: weight loss and appetite reduction were not related to gastric emptying delay or GI side effects (P>0.05 for each).
That leaves the appetite-suppressing effect resting mostly on something else — most likely central signaling in the brain, since these drugs act on GLP-1 receptors in appetite-regulating regions of the hypothalamus and brainstem, not primarily on the gut wall. But none of the trials retrieved here isolated and quantified that central mechanism directly; they mainly ruled out gastric emptying as the main explanation.
Some people are simply hungrier than the average suggests
A 2026 narrative review searching for predictors of GLP-1 response found that non-response — commonly defined as losing less than 5% of total body weight — affects roughly 10% of participants in controlled obesity trials, with real-world cohorts suggesting an even higher rate outside trial conditions. The review also flagged early findings from a genome-wide association study linking variation in the GLP1R gene (the drug's own target) to both weight-loss efficacy and GI tolerability, and GIPR gene variants to nausea and vomiting specifically with tirzepatide. The authors were explicit that these findings are self-reported, from a single cohort, and unreplicated — "hypothesis-generating rather than a basis for individual-level genotyping." Their conclusion: no single baseline characteristic currently predicts who will respond well and who won't. The best available signal is how someone responds in the first weeks of treatment, not anything that can be measured beforehand.
What we don't know yet
What actually drives the appetite effect, if not the stomach. Trials have repeatedly ruled out gastric emptying as the primary mechanism but have not directly quantified the central nervous system pathways in humans at the resolution needed to explain the remaining 94-96% of the effect.
Who will be a low- or non-responder, before treatment starts. No baseline test — genetic, hormonal, or behavioral — has been validated to predict which roughly 1 in 10 people will lose less than 5% of body weight.
Whether appetite suppression fades over time on treatment. The feeding studies referenced here mostly ran 16-20 weeks. Whether the same magnitude of hunger reduction persists at 1, 2, or 3 years on stable dosing was not tested by these trials.
What happens to appetite after stopping. None of the appetite-specific feeding trials followed participants after treatment discontinuation to see whether hunger signaling returns to baseline, overshoots it, or settles somewhere in between.
Whether tirzepatide's appetite mechanism matches semaglutide's. The controlled ad libitum meal-test data retrieved here come from semaglutide and liraglutide trials. Tirzepatide's dual GLP-1/GIP mechanism has been linked to appetite reduction in review literature, but comparable meal-test quantification for tirzepatide was not identified in this search.
Sources
- Friedrichsen M, Breitschaft A, Tadayon S, Wizert A, Skovgaard D. The effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying in adults with obesity. Diabetes, Obesity and Metabolism, 2021;23(3):754-762. DOI
- Gabe MBN, Breitschaft A, Knop FK, et al. Effect of oral semaglutide on energy intake, appetite, control of eating and gastric emptying in adults living with obesity: A randomized controlled trial. Diabetes, Obesity and Metabolism, 2024;26(10):4480-4489. DOI
- Gibbons C, Blundell J, Tetens Hoff S, Dahl K, Bauer R, Baekdal T. Effects of oral semaglutide on energy intake, food preference, appetite, control of eating and body weight in subjects with type 2 diabetes. Diabetes, Obesity and Metabolism, 2020;23(2):581-588. DOI
- Friedman MI, Harmsen WS, Camilleri M. Appetite Suppression by GLP-1 Receptor Agonists: Role of Delayed Gastric Emptying. Obesity (Silver Spring), 2026;34(8):1535-1540. DOI
- Quast DR, Nauck MA, Schenker N, Menge BA, Kapitza C, Meier JJ. Macronutrient intake, appetite, food preferences and exocrine pancreas function after treatment with short- and long-acting glucagon-like peptide-1 receptor agonists in type 2 diabetes. Diabetes, Obesity and Metabolism, 2021;23(10):2344-2353. DOI
- Kuryłowicz A, Czupryniak L. Responders Vs. Non-Responders or How to Predict the Response to GLP-1 or GLP-1/GIP Receptor Agonist Therapy. Diabetes, Obesity and Metabolism, 2026. DOI
Article records maintained via PubMed. Peptide Proof reports what studies found. It does not provide medical advice, dosing guidance, or treatment recommendations.
Topic: Weight & Metabolism | Evidence Index: semaglutide · tirzepatide · liraglutide
Sources
- Effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying
- Diabetes, Obesity and Metabolism, 2021 · n=72 · DOI
- Effect of oral semaglutide on energy intake, appetite, control of eating and gastric emptying in adults living with obesity
- Diabetes, Obesity and Metabolism, 2024 · n=61 · DOI
- Effects of oral semaglutide on energy intake, food preference, appetite, control of eating and body weight in subjects with type 2 diabetes
- Diabetes, Obesity and Metabolism, 2020 · n=15 · DOI
- Appetite Suppression by GLP-1 Receptor Agonists: Role of Delayed Gastric Emptying
- Obesity (Silver Spring), 2026 · n=40 · DOI
- Macronutrient intake, appetite, food preferences and exocrine pancreas function after treatment with short- and long-acting GLP-1 receptor agonists
- Diabetes, Obesity and Metabolism, 2021 · n=50 · DOI
- Responders Vs. Non-Responders or How to Predict the Response to GLP-1 or GLP-1/GIP Receptor Agonist Therapy
- Diabetes, Obesity and Metabolism, 2026 · DOI
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