What really controls our appetite – hunger, stress or habit? | Health & wellbeing

IImagine you’re in a meeting room when someone brings out the cookies – a packet of Jammie Dodgers, perhaps, or a nice little plate of custards. Maybe you want one or maybe you don’t, but it’s likely that the people around you will all react differently: someone will grab a few right away, someone else will eat one without seeming to notice, another will barely realize the cookies exist, and someone will spend the entire meeting wanting one but won’t take it. Our appetites and reactions to food vary wildly – ​​but what goes on behind the scenes to govern them? And has modern food hijacked the process in some way? Grab a cookie (or not) and settle in.

“First of all, it’s important to distinguish between hunger and appetite,” says Giles Yeo, professor of molecular neuroendocrinology at the University of Cambridge and author of Why Calories Don’t Count. “Hunger is a feeling – it’s what happens before you decide you need to eat something. Appetite is everything surrounding why we eat – including hunger, fullness and reward, or what you actually feel when you eat. These three sensations all use completely different parts of the brain, but they all work together.”

Hunger is regulated by the hypothalamus, located behind the bridge of the nose at the base of the brain, which monitors your body’s blood sugar levels and the hormones leptin and ghrelin to check if you are in an energy deficit. Satiety is regulated by the hindbrain, located roughly where your skull meets your neck: When your stomach stretches, the vagus nerve sends a signal to this area telling you that you are physically full. Reward, for its part, is regulated by a diffuse network of neurons located higher in the brain, driven by dopamine and its search for pleasant activities.

“All these parts of the brain communicate with each other, which is why if you’re really hungry, food that offers very little ‘reward’ – like rice or bread – can be delicious. Or why you can feel full but still feel ready for chocolate cake, because it activates your reward system even though your hindbrain says you’re full,” Yeo explains. “It’s like a triangle that changes shape depending on your situation, with appetite in the middle.”

So what’s going on with the cookies? Well, part of the reason we may react to it differently is how hungry or full we are at the time, but it’s likely that genetics also play a role. “We all know people who love food and people who just view it as fuel,” Yeo continues. “People who consume food will eventually feel hungry, but this happens much closer to when they actually need to eat than for others. It’s also likely to depend on how much – or how little – food is needed to trigger the brain’s reward response. We know there are over a thousand genes that influence our appetite, so it’s a very complex system.”

Another part of all this is that olfactory, visual, and even sound cues activate the brain’s appetite circuits regardless of how much energy we have stored, resulting in what neuroscientists call “hedonic” hunger. “When we observe food, sensory and olfactory inputs interact with regions of the brain that regulate appetite and temporarily increase dopamine signaling,” explains nutritional neuroscientist Timothy Frie. “It increases our motivation to eat, even if our physiological energy needs have already been met. The feeling of hunger comes not from an empty stomach, but from a conditioned and motivated response by which the brain and body prepare for ingestion based on what you see. Sound may also play a role, its influence coming primarily from learned associations, such as the repeated association of a sizzling or crunchy sound with a desirable taste or sensation.”

Another complication is that all of these systems can be disrupted, or at least disrupted, by stress. “When we are stressed or experience some degree of cognitive overload or fatigue, the regulatory capacity of our prefrontal cortex is reduced, while the appetite and reward systems remain active,” explains Frie. “The brain’s demand for a quick, reliable source of fuel also increases in response to stress. This creates a predictable imbalance: a stronger urge to eat with a reduced ability to regulate that urge.” Sweet, salty, fatty, and especially ultra-processed foods quickly increase glucose availability and illuminate motivational pathways in the brain, and when we are stressed, the brain places a higher priority on these foods because they provide quick and efficient energy.

Appetite may also be disrupted over time. When we frequently consume refined carbohydrates, sugars and fats over a long period of time, our insulin and leptin receptors (which regulate energy balance and appetite) can become inhibited, reducing their responsiveness and making it more difficult to determine when we should stop eating.

Food companies, of course, know all this and often respond by subverting the systems that lead us astray: by wafting delicious scents into the air at fast food restaurants, for example, or by designing foods that combine hyperpalatability with sensory cues like a satisfying crunch. To make matters worse, although our built-in satiety systems are pretty good at roughly estimating the energy content of foods that contain mostly fat or protein, they are poor at estimating it in foods that mix refined carbohydrates and fats, making it easier to overeat on things like cookies, pastries, and pizza.

Where does this leave us? Unfortunately, in a situation where our basic drives and biological mechanisms have not changed much from our hunter-gatherer past, but are exploited by the infinite food options available. “Many of us live in a supernormal, overstimulating, artificial eating environment,” says Frie. “Our brains are saturated with cues to eat, but they aren’t necessarily equipped to respond to that many cues for a long period of time. The best thing we can do for ourselves is to develop what I call food-mind mastery: the ability to recognize what is motivating the urge to eat in that moment and respond to it with awareness and conscious intention.”

This allows us to regulate and manage the sequence of events that occur between a food signal and a food response. In practice, Frie explains, “This might mean inserting a brief pause before acting on the impulse to eat and asking a single question: ‘What is generating this signal right now: need for energy, stress, habit, or exposure to a signal?’ This step engages our prefrontal cortex, which allows us to shift our behavior from automatic to intentional.

But while the vast majority of non-infectious diseases we face as a species are diet-related, preaching personal responsibility probably isn’t enough. “Personal responsibility is good and we need to talk about it and give people advice,” Yeo says. “But I also think it frees policymakers and government from the public health decisions they have to make to try to improve our food environment. It has to be a holistic thing.”