🟠 Moderate Evidence
Hunger is far more complex than an empty stomach—your brain, hormones, and gut bacteria all send overlapping signals that regulate appetite and food intake. Research published in The New England Journal of Medicine (2025) distinguishes three distinct systems: homeostatic hunger (driven by energy balance), hedonic hunger (driven by reward and pleasure), and microbiota-driven hunger (shaped by gut bacteria). Understanding these mechanisms offers new insights into why people eat, when they feel full, and how metabolic dysfunction can lead to overeating and weight gain.
Key takeaways
- Homeostatic hunger is regulated by hormones—ghrelin stimulates appetite while leptin, GLP-1, PYY, and CCK promote satiety—to match energy intake with metabolic demands
- Hedonic hunger is triggered by food reward signals, emotions, and habits, independent of actual energy needs, and can override natural fullness cues
- Gut microbes produce metabolites that influence hunger and satiety hormones, linking microbiota composition to appetite regulation and metabolic control
Study at a Glance
| Source | The New England Journal of Medicine |
| Study type | Narrative review / Physiological framework |
| Focus | Three distinct hunger systems and their neuroendocrine mechanisms |
| Author | Prof. Alessio Fasano, Harvard Medical School |
| Year | 2025 |
The Three Hunger Systems and Their Primary Drivers
Hormonal regulators and signals in each appetite system
Source: Fasano, A., The New England Journal of Medicine (2025) | Georgian Medical Journal News
Homeostatic Hunger: Your Body’s Energy Gauge
Homeostatic hunger is the system your body uses to match food intake with energy expenditure and physiological demands. According to Prof. Alessio Fasano, Harvard Medical School, writing in The New England Journal of Medicine (2025), this system operates through coordinated hormonal signals that increase or decrease appetite based on metabolic state.
When your stomach is empty or energy reserves are depleted, cells in the gastric mucosa release ghrelin, which travels to the hypothalamus and triggers hunger sensations. Conversely, when energy stores are replenished, leptin released from adipose tissue signals satiety. Additional hormones amplify this signal: peptide YY (PYY) and glucagon-like peptide-1 (GLP-1), released from intestinal cells, further suppress appetite, while cholecystokinin (CCK) from the small intestine contributes to early satiety. Together, these hormones create a homeostatic feedback loop that aligns food intake with energy needs.
This system evolved to prevent both starvation and energy surplus. After prolonged exercise, homeostatic hunger escalates to restore glycogen and repair muscle tissue. During periods of caloric restriction, ghrelin levels rise sharply while leptin declines, driving compensatory hunger until energy balance is restored. Clinical research on appetite regulation shows this system is highly sensitive to metabolic state, making it reliable for normal-weight individuals with intact hormonal signalling.
Hedonic Hunger: The Reward-Driven Override
Hedonic hunger operates independently of energy needs and is driven by the brain’s reward systems. Unlike homeostatic hunger, which responds to metabolic signals, hedonic hunger is triggered by external cues—the sight of dessert, the aroma of baked goods, emotional stress, or ingrained eating habits. Fasano notes that this system engages dopamine and opioid pathways in the nucleus accumbens and orbitofrontal cortex, regions associated with pleasure and reinforcement.
Foods high in sugar, fat, and salt are potent activators of hedonic hunger because they trigger robust dopamine release—a response evolutionarily advantageous in environments of food scarcity but harmful in modern food-abundant settings. Critically, hedonic hunger can override satiety signals. A person who has just finished dinner may experience no metabolic hunger (homeostatic hunger is satisfied), yet hedonic hunger pushes them to eat dessert anyway. This dissociation is especially pronounced in individuals with obesity or eating disorders, where reward sensitivity to palatable foods is heightened.
Emotional states powerfully modulate hedonic hunger. Stress, anxiety, boredom, and sadness can activate reward-seeking eating behaviour independent of ghrelin or leptin levels. This explains why people often reach for comfort food during emotional distress, a phenomenon well-documented in psychological and metabolic research. The challenge is that hedonic hunger generates weak satiety signals—eating highly palatable food rarely feels “complete,” encouraging overconsumption.
Microbiota-Driven Hunger: The Bacterial Influence
Recent evidence reveals that your gut microbiota plays an active role in appetite regulation. According to Fasano’s 2025 framework, gut bacteria produce metabolites—particularly short-chain fatty acids (SCFA), secondary bile acids, and lipopolysaccharides (LPS)—that influence hunger hormones and brain signalling. These bacterial products modulate ghrelin secretion, enhance GLP-1 and PYY release, and even cross the blood-brain barrier to affect hypothalamic appetite centres directly.
Dysbiosis (imbalanced microbiota composition) can disrupt these signals, tipping the balance toward increased appetite or weakened satiety. Certain bacterial taxa favour energy conservation and hunger promotion, while others enhance satiety signalling. For example, bacteria that produce butyrate (a key SCFA) enhance GLP-1 secretion and improve glucose control, thereby reducing hedonic food-seeking. Conversely, dysbiotic states enriched in lipopolysaccharide-producing bacteria may promote systemic inflammation and blunt satiety signalling. This mechanism links gut microbiota composition to metabolic health and appetite control, opening new avenues for dietary and probiotic interventions.
The microbiota-driven system is particularly relevant to understanding obesity and metabolic syndrome, where dysbiosis often co-occurs with impaired satiety and increased hedonic food preferences. Fasano emphasizes that all three hunger systems interact—dysbiosis may amplify hedonic hunger while suppressing homeostatic satiety, creating a “perfect storm” for weight gain and overeating.
Hunger is not a single signal but three distinct, sometimes competing systems—homeostatic energy balance, hedonic reward-seeking, and microbiota-derived metabolic signalling—that together determine when and how much we eat.
— Prof. Alessio Fasano, Harvard Medical School (The New England Journal of Medicine, 2025)
What this means
Frequently asked questions
Is hunger always a sign that I need to eat?
No. Homeostatic hunger (true metabolic need) can be distinguished from hedonic hunger (reward-seeking) by context. If you’ve eaten recently and feel full but see cake and want it, that’s hedonic hunger. Homeostatic hunger typically increases gradually over hours and disappears quickly after eating balanced food. Mindful eating practices—pausing to assess whether you’re physically or emotionally hungry—help clarify which system is active.
Can I change my gut microbiota to reduce appetite?
Yes, evidence increasingly supports this. High-fibre diets, fermented foods (yoghurt, sauerkraut, kimchi), and prebiotic supplements (inulin, FOS) promote bacteria that enhance satiety hormone production. Regular sleep, stress reduction, and avoiding unnecessary antibiotics also preserve beneficial microbiota. However, changes take weeks to months, and individual responses vary based on baseline dysbiosis and diet adherence.
Why is emotional eating so hard to control?
Hedonic hunger engages the same brain reward pathways as addiction—dopamine release during stress-eating creates a learned association between negative emotion and food pleasure. Willpower alone is insufficient because this system evolved to prioritise survival reward-seeking over rational decision-making. Effective strategies combine cognitive-behavioural therapy, stress management (exercise, meditation), and environmental design (removing trigger foods), rather than relying on self-control.
The integration of homeostatic, hedonic, and microbiota-driven hunger into a single framework reshapes our understanding of appetite and obesity. Rather than attributing overeating solely to lack of discipline, clinicians and policymakers can now target specific dysfunctional pathways—whether metabolic, psychological, or microbial—with tailored interventions. Future research should focus on how these three systems interact in individuals with different metabolic phenotypes and how precision dietary and microbial therapies can restore balanced appetite control.
Source: Three types of hunger explained simply (Fasano, A., The New England Journal of Medicine, 2025)
Was this article helpful?
Disclaimer. This article is health journalism intended for general information and education. It is not medical advice and is not a substitute for professional diagnosis or treatment. Always consult a qualified healthcare provider about your individual circumstances. Full disclaimer →
Related Coverage
Editorial standards. This article was produced under the GMJ News editorial process, with oversight by the GMJ Editorial Board. Our editorial process. Spotted an error? Contact the editorial team.
