The Science of Appetite: How Hunger, Stress and Habit Control Our Eating
Imagine you are in a meeting room when someone brings out a plate of biscuits—perhaps Jammie Dodgers or custard creams. You might want one, or you might not, but the people around you will likely respond in diverse ways. One person grabs a couple immediately, another eats one absentmindedly, a third barely notices the biscuits exist, and someone else spends the entire meeting resisting the temptation. Our appetites and reactions to food vary dramatically, but what underlying mechanisms govern these differences? And has contemporary food production hijacked these processes? Settle in with a biscuit (or without) as we explore the science behind our eating behaviours.
Distinguishing Hunger from Appetite
First, it is crucial to differentiate between hunger and appetite, says Giles Yeo, a professor of molecular neuroendocrinology at the University of Cambridge and author of Why Calories Don’t Count. "Hunger is a feeling—it is what occurs before you decide you need to eat something. Appetite encompasses everything surrounding why we eat, including hunger, fullness, and reward, or how you actually feel when you consume food. These three sensations utilise completely different brain regions, yet they all collaborate."
Hunger is regulated by the hypothalamus, located behind the bridge of the nose at the brain's base, which monitors blood sugar levels and hormones like leptin and ghrelin to detect energy deficits. Fullness is controlled by the hindbrain, situated where the skull meets the neck; when the stomach stretches, the vagus nerve signals this area to indicate physical satiety. Reward, meanwhile, is managed by a diffuse network of neurons higher in the brain, driven by dopamine in pursuit of pleasurable activities.
"All these brain parts communicate, which explains why, when you are truly hungry, even low-reward foods such as rice or bread can taste delicious. Or why you might feel full yet still desire chocolate cake, as it activates your reward system despite your hindbrain signalling satiety," Yeo explains. "It resembles a triangle that shifts shape based on circumstances, with appetite at its centre."
Genetic Influences and Hedonic Hunger
So, what accounts for the varied responses to biscuits? Partly, it depends on immediate hunger or fullness, but genetics also play a significant role. "We all know individuals who adore food and others who view it merely as fuel," Yeo continues. "Food-is-fuel people tend to experience hunger much closer to when they actually need to eat. It likely relates to how much or how little food is required to trigger the brain's reward response. Over a thousand genes influence our appetite, making it an exceedingly complex system."
Another factor is hedonic hunger, where scent, sight, and even sound cues activate appetite circuits independently of energy stores. "When we see food, sensory and olfactory inputs interact with brain regions regulating appetite, temporarily boosting dopamine signalling," says Timothy Frie, a nutritional neuroscientist. "This heightens our motivation to eat, even if physiological energy needs are already met. Hunger arises not from an empty stomach but from a conditioned, cue-driven response where the brain and body prepare for intake based on visual stimuli. Sound also contributes through learned associations, like pairing a sizzle or crunch with a desirable taste."
The Impact of Stress and Modern Food Environments
Stress further complicates these systems by disrupting regulation. "When stressed or cognitively overloaded, the prefrontal cortex's regulatory capacity diminishes, while appetite and reward systems stay active," Frie notes. "The brain's demand for rapid fuel also increases under stress, creating an imbalance: a stronger drive to eat with reduced ability to regulate it." Sugary, salty, fatty, and ultra-processed foods quickly elevate glucose and activate motivation pathways, with the brain prioritising these items during stress for their efficient energy provision.
Appetite can also be disrupted over time. Frequent overconsumption of refined carbs, sugars, and fats can mute insulin and leptin receptors, reducing responsiveness and making it harder to recognise when to stop eating. Food companies often exploit these vulnerabilities, for instance, by dispersing enticing scents in fast-food outlets or crafting hyperpalatable foods with satisfying textures like a crunch.
Compounding this, our satiety systems are adept at estimating energy in mostly fat or protein foods but poor at judging mixtures of refined carbs and fat, facilitating overeating of items like biscuits, pastries, and pizza.
Navigating a Supernormal Food Environment
Consequently, we inhabit a scenario where ancient biological drives are exploited by an abundance of food options. "Many of us live in a supernormal, overstimulating, and engineered food environment," Frie asserts. "Our brains are inundated with eating cues but ill-equipped to handle them long-term. The best approach is developing food-mind fluency: the ability to identify what drives the urge to eat in any moment and respond with awareness and conscious intention."
This involves regulating the sequence between a food cue and response. "In practice, that might mean pausing briefly before acting on an impulse and asking: 'What generates this signal now: energy need, stress, habit, or exposure to a cue?'" Frie suggests. "This step engages the prefrontal cortex, shifting behaviour from automatic to intentional."
However, with most non-infectious diseases being diet-related, personal responsibility alone may be insufficient. "Personal responsibility is important, and we must discuss it and offer advice," Yeo states. "But it also absolves policymakers and governments from necessary public health decisions to improve our food environment. It has to be a holistic endeavour."
