Exenatide powerfully suppressed food intake in rhesus macaques while initially preserving their hedonic experience and food anticipation — suggesting GLP-1 drugs separate the act of eating from the pleasure of food.
Anticipatory effect completely erasedExenatide eliminated monkeys' normal tendency to adjust eating based on expected future food quality, while preserving taste preferences
What the researchers found
Acute exenatide (1 μg/kg subcutaneous) administered 1 hour before the first feeding session reduced food intake to uniformly very low levels across all meal schedule conditions, completely eliminating the anticipatory effect — where monkeys normally eat less in session 1 when expecting preferred food in session 2.
Exenatide induced hypoglycemia in a meal-schedule-dependent anticipatory pattern, suggesting metabolic anticipation was preserved even as eating behavior was suppressed. In the second feeding session, the positive contrast effect (preference for tastier food) was preserved but with a weaker residual effect specifically on consumption of the more palatable pellet. The authors conclude exenatide's effects evolve temporally from strong anorectic (appetite-suppressing) to weak anhedonic (pleasure-dampening) modulation.
Why it matters
One of the biggest concerns about GLP-1 weight loss drugs is whether they work by making food less pleasurable — which could contribute to depression or anhedonia in some patients. This study provides nuanced evidence that GLP-1 agonists primarily suppress the drive to eat while initially preserving hedonic experience, with pleasure-dampening effects appearing later and more weakly. Understanding this distinction is crucial for predicting psychological side effects.
How the study worked
Five adult male rhesus macaques were tested using a novel operant food intake paradigm with four meal schedule conditions. Two pellet types with different palatability values were offered in all combinations across two consecutive daily feeding sessions. Exenatide (1 μg/kg) was administered subcutaneously 1 hour before the first session. Food intake, pellet preferences, and blood glucose were measured across conditions.
What this study cannot tell us
The study used only 5 male rhesus macaques, which is a very small sample size even for primate research. Only a single acute dose was tested — chronic dosing may produce different effects on hedonic regulation. The translation from macaque food preference behavior to human subjective experience of food pleasure is uncertain. Blood glucose changes (hypoglycemia) may have independently influenced feeding behavior.
How to read the evidence
This is a preclinical study in 5 non-human primates with a well-designed behavioral paradigm. While primate studies are more translatable than rodent work, the very small sample size and single-dose design limit the strength of conclusions.
When this study was published
Published in 2024, this is a very recent study addressing timely questions about the psychological mechanisms of GLP-1 drugs as their use for weight management explodes globally.
The bigger picture
As millions of people take GLP-1 agonists for weight loss, understanding exactly how these drugs change the brain's relationship with food is increasingly important. Reports of reduced interest in food, alcohol, and other pleasures have raised questions about whether GLP-1 drugs affect the reward system broadly. This primate study provides some of the most detailed behavioral evidence to date, showing the effects are more nuanced than simple appetite suppression.
Questions still open
- Does chronic GLP-1 agonist treatment shift the balance further toward anhedonic effects, potentially explaining reports of reduced food enjoyment in long-term users?
- Could the uncoupling of hedonic experience from eating behavior explain why some patients on GLP-1 drugs report feeling emotionally detached from food?
- Does the exenatide-induced hypoglycemia observed in this paradigm contribute to the appetite suppression or represent a separate metabolic effect?
Common questions
Does exenatide make food less enjoyable or just reduce appetite?
Why does this matter for people taking GLP-1 drugs for weight loss?
Read the original research
GLP-1 receptor agonist exenatide uncouples food intake from hedonic and anticipatory regulation in non-human primates: insights from an operant meal schedule paradigm.
Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 50(2), 410-418
Citation
Knakker, Balázs; Inkeller, Judit; Kovács, Péter; Lendvai, Balázs; Hernádi, István. (2024). GLP-1 receptor agonist exenatide uncouples food intake from hedonic and anticipatory regulation in non-human primates: insights from an operant meal schedule paradigm.. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 50(2), 410-418. https://doi.org/10.1038/s41386-024-01981-5