What neuroscience reveals about eating behaviour

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Why do we eat when we are not actually hungry? Why can we finish a meal feeling completely satisfied and still somehow find room for something we find irresistible? Why does listening to our body feel easy on some days, while on others it seems as though food is making the decisions for us?

Perhaps because eating has never been just about eating.

Behind something as ordinary as opening the fridge, choosing a food or deciding that we have had enough, there is a constant conversation taking place between the brain, hormones, the digestive system, our energy stores, our environment, our emotions, our habits and our reward circuits.

And understanding that conversation can change something important.

Because the better we understand why we do what we do, the less we need to judge ourselves for doing it.

The neuroscience of eating allows us to look at our behaviour from a different perspective: not to turn every meal into an equation, but to better understand the biological and environmental forces involved in our decisions.

And perhaps, from there, to choose with a little more awareness.

The brain does not simply wait until we are hungry

Our body is designed to survive.

For much of our evolutionary history, finding food was never guaranteed. Being able to store energy when food was available and use it when it became scarce was an extraordinary advantage for survival.

The problem is that our brain still carries many of those mechanisms into a completely different world.

Today, we do not need to chase our food. We find it in supermarkets, restaurants, apps, shop windows and advertisements. We have access to highly energy-dense foods at almost any time of day.

Our brain is ancient. Our environment is not.

And that mismatch helps explain a great deal.

The brain is constantly involved in deciding when to eat, how much to eat and when to stop. To do this, it receives information from many different sources.

On the one hand, there are internal signals: glucose availability, the state of our energy stores and hormones related to hunger and satiety.

On the other, there are external signals: the smell of food, its appearance, the time of day, the social context, our emotions or even an image appearing on a screen.

Much of this information converges in the hypothalamus, a structure that plays a fundamental role in regulating hunger, metabolism and energy homeostasis: the balance between the energy we take in and the energy we use.

When we need energy, signals appear that encourage us to seek food. When we have eaten enough, other signals contribute to the feeling of satiety.

It sounds simple.

But only in theory.

Because our eating behaviour does not depend exclusively on our energy needs. Stress, habits, highly palatable foods, emotions, the constant availability of food and advertising can all influence this system.

To understand why, we first need to understand something more basic:

What does our body do with energy when it does not need it immediately?

The body stores energy: glycogen and triglycerides

We do not need to eat continuously because our body has systems designed to store energy.

In simple terms, we can think of two major reserves: one that is more immediately available and another designed to sustain us over longer periods of time.

Glycogen: short-term available energy

When we eat, we obtain glucose, one of the main fuels used by our cells.

When glucose is available, insulin, released by the pancreas, helps facilitate its use and storage. Some of that glucose can be converted into glycogen, which is stored mainly in the liver and muscles.

The liver can store approximately 100 to 200 grams, while the muscles can hold larger amounts — around 400 to 700 grams, depending on factors such as muscle mass, diet and training.

The process of storing glucose as glycogen is known as glycogenesis.

When we need that energy again, the reverse process takes place: glycogenolysis, through which glycogen is broken down so that the stored energy can be used.

Glucagon, another hormone produced by the pancreas, also plays an important role in regulating blood glucose levels.

Muscle glycogen becomes particularly important during physical activity. When we run, lift weights or perform intense exercise, our muscles can quickly draw on these reserves.

This is why, after significant physical effort, replenishing glycogen stores through food — particularly carbohydrates — can be relevant for recovery and subsequent performance.

But our body has another, much larger energy store.

Triglycerides: our long-term reserve

When we need to draw on larger energy reserves, adipose tissue comes into play.

Triglycerides are made up of one glycerol molecule attached to three fatty acids, which may include fatty acids such as stearic, oleic or palmitic acid.

They are stored mainly inside cells called adipocytes.

And these cells have a fascinating characteristic: they can increase considerably in size as they store triglycerides.

When the body needs to mobilise this energy, a process called lipolysis takes place, breaking triglycerides down into glycerol and fatty acids. These components can then enter different metabolic pathways to provide energy for the body.

Triglycerides therefore represent an extraordinarily important energy reserve.

But our modern environment introduces a paradox.

We have a body that is remarkably well designed to store energy in anticipation of future periods of scarcity, while at the same time living surrounded by food.

The body is still prepared for scarcity in a world that offers abundance.

And this brings us to a fundamental distinction.

Not all hunger means the same thing

Broadly speaking, we can distinguish between homeostatic hunger and non-homeostatic hunger.

The first is related to the body's energy requirements.

The second opens up a far more interesting question:

What happens when we want to eat even though, energetically, we do not need to?

Before we get there, we need to understand how the body detects that it needs energy in the first place.

Homeostatic hunger: when the body seeks balance

Energy homeostasis regulates the balance between the energy we consume and the energy we expend.

If we take in more energy than we use, the body can store it. If we expend more than we consume, the body gradually draws on its reserves to maintain its functions.

This is why we have mechanisms that encourage food intake when energy availability decreases and others that help us stop eating once we have consumed enough.

But hunger does not appear because a single switch has been turned on.

It is the result of multiple signals reaching the brain at the same time.

Environmental signals

The smell of food. Its appearance. The size of a portion. Watching someone else eat. The time of day. A family habit.

All of these things can influence our eating behaviour.

We sometimes imagine that hunger comes first and then we look for food.

But it can also happen the other way around: we see food, and then the desire to eat appears.

Gastrointestinal signals and ghrelin

When we have gone for some time without eating, a particularly interesting hormone enters the picture: ghrelin.

Its levels tend to rise during fasting and before meals and decrease after eating. It acts as a signal that promotes hunger and food-seeking behaviour.

And there is something particularly fascinating about it: ghrelin can increase before the times at which we habitually eat.

This helps explain why we may begin to feel hungry at roughly the same time every day.

The body does not simply respond.

It also learns and anticipates.

This signal is so powerful that, in experimental studies, the administration of ghrelin has even been associated with an increase in food-related thoughts and mental imagery.

Metabolic signals

The body also has mechanisms capable of detecting nutrient availability.

Both the liver and the nervous system participate in this metabolic monitoring. Information from different peripheral sensors can be communicated to the brain, among other pathways, through the vagus nerve, while the brain itself also contains mechanisms sensitive to our energy state.

When the system detects that fuel availability is falling, the motivation to seek food increases.

But if there are so many signals designed to make us eat, there must also be something that tells us:

that is enough.

Satiety: how does the brain know when to stop?

Satiety is not simply the feeling of having a full stomach.

It is the result of a complex integration of signals produced by the presence of nutrients, distension of the digestive system, intestinal hormones and information reaching the brain.

Many of these signals travel through vagal afferents to structures such as the nucleus of the solitary tract (NTS), which is involved in integrating visceral and gustatory information and in mechanisms related to satiety.

We can distinguish between signals that act in the short term, helping us finish an individual meal, and mechanisms involved in regulating energy balance over the long term.

Short-term satiety signals

While we eat, the digestive system is far from passive.

There are receptors capable of detecting nutrients in the stomach and intestine and transmitting that information to the brain.

The composition of a meal also influences how satiating it is. Generally speaking, foods high in protein and certain fibre-rich foods tend to produce a strong satiety response.

Different hormones are also involved.

Insulin, in addition to its fundamental role in glucose metabolism, participates in communicating the body's energy state to the brain.

Cholecystokinin (CCK) is released in the small intestine shortly after we begin eating, particularly in response to fats and proteins. Among its other functions, it contributes to slowing gastric emptying and participates in satiety signalling.

Peptide YY (PYY) also increases after meals and contributes to reducing food intake and altering gastrointestinal motility.

In other words, while we are simply thinking I'm eating, an extraordinarily sophisticated conversation is taking place inside the body.

And that conversation continues long after we leave the table.

Leptin: a long-term signal

The signals generated by a single meal are only one part of the system.

The brain also needs information about the body's energy reserves over time.

This is where leptin enters the picture.

Leptin is a hormone produced mainly by adipocytes. Its levels are related to the amount of adipose tissue in the body, and it acts on different regions of the brain, including the hypothalamus.

One particularly important structure is the arcuate nucleus (ARC).

When leptin binds to its receptors, it participates in signalling cascades involved in regulating appetite and energy expenditure.

And here we encounter an apparent contradiction.

People with obesity often have higher concentrations of leptin. Yet high levels of this hormone do not necessarily translate into a proportional reduction in hunger.

One explanation that has been extensively studied is leptin resistance: a reduced response by the body and brain to leptin's signal.

So it is not enough to ask how much of a hormone is present.

What also matters is how well the brain is listening to that signal.

Up to this point, we might think we have the explanation: ghrelin promotes hunger; leptin, insulin, CCK, PYY and other signals contribute to the regulation of satiety; the brain receives the information and we act accordingly.

But then a question appears that disrupts the whole model:

If we have enough energy, why do we still want to eat?

This is where non-homeostatic hunger comes in.

In theory, we could imagine that we eat when our energy stores fall and stop when they have been sufficiently replenished.

But human beings do not work like that.

We eat at certain times because we have learnt to. We eat because we are celebrating. Because we are bored. Because we are nervous. Because something smells incredible. Because somebody has put food in front of us. Because we are used to having something while watching a film.

Even our subjective experience of hunger can vary enormously and does not precisely represent the amount of energy stored in our body.

Because eating behaviour does not depend solely on metabolic biology.

It is also influenced by sensory signals, such as smell, taste and texture; by our emotional state, including stress, anxiety or wellbeing; and by context, routines, social company and the availability of food.

We do not always eat because the body needs energy. Sometimes we eat because the brain has learnt that this moment means food.

And this is where other regions of the brain become involved.

When eating stops being simply a matter of hunger

Several areas of the cerebral cortex are particularly relevant when trying to understand eating behaviour that is not strictly homeostatic.

The prefrontal cortex: the space between impulse and action

The prefrontal cortex (PFC) is involved in executive functions such as planning, decision-making and inhibitory control.

In very simple terms, it is one of the regions that can help us create a pause between I want this and I'm going to do it.

Research into binge-eating disorder has described alterations in circuits associated with inhibitory control and responses to food-related stimuli.

Some studies have also observed that leptin can modify activity in cortical regions involved in regulating eating behaviour.

This is particularly interesting because it reminds us that hormones related to energy do not act exclusively on basic hunger centres.

Biology, reward and decision-making are far more interconnected than they may seem.

The orbitofrontal cortex: how valuable is this food to me?

The orbitofrontal cortex (OFC) is involved in evaluating rewards.

We do not simply perceive food.

Our brain also evaluates how much we want it.

This region participates in representing the rewarding value of food and in phenomena such as sensory-specific satiety.

You have probably experienced this before: after eating a considerable amount of one particular food, it begins to seem less appealing, while a different flavour may still sound tempting.

It is not simply a lack of willpower.

It is the brain processing reward.

The insula: listening to what is happening inside

The insula integrates sensory information with signals coming from inside the body.

It is involved in taste perception, the representation of bodily states and the integration of information related to hunger and satiety.

In a way, it helps the brain respond to a fundamental question:

What is happening inside me while this is happening outside?

And perhaps this is why understanding eating inevitably leads us towards something that goes far beyond calories.

Our experience of the body.

Why can eating make us feel so good?

Because food is not only energy.

It can also be reward.

Highly palatable foods — particularly those designed to combine flavours, textures and high concentrations of fat, sugar or salt — can strongly activate brain systems involved in motivation and reward.

This is where dopamine comes in.

Dopaminergic activity in circuits such as the mesolimbic pathway and regions including the nucleus accumbens is involved in motivation, reward learning and the desire to repeat certain behaviours.

Endogenous opioids and endocannabinoids are also involved in the hedonic and motivational aspects of eating.

And this brings us to an important distinction when trying to understand our behaviour:

Needing something and wanting something are not exactly the same thing.

We may not energetically need a particular food and still desire it intensely.

Reward circuits also maintain connections with hypothalamic regions involved in food intake, including the lateral hypothalamus.

This means that the systems regulating energy and those regulating reward do not exist separately.

They communicate.

Leptin and insulin can modulate the sensitivity of reward circuits. When energy is restricted and certain signals associated with energy availability decrease, food-related stimuli can become even more relevant.

From an evolutionary perspective, this makes perfect sense.

If you have not eaten for some time, finding food should become a priority.

The problem arises when a system designed to drive us towards food during periods of need operates within an obesogenic environment, where highly energy-dense, appealing foods are constantly available.

Never before have we had so much food around us while simultaneously being exposed to so many signals telling us to eat.

In this environment, reward circuits can encourage food intake even when there is no immediate energetic need.

The hypothalamus: where many of these signals meet

To understand this system even better, we need to return to the hypothalamus and, more specifically, the arcuate nucleus (ARC).

Here we find neuronal populations with opposing but complementary functions.

On the one hand, there are orexigenic neurons, which promote food intake and produce molecules such as neuropeptide Y (NPY) and agouti-related peptide (AgRP).

On the other, we find POMC neurons, associated with anorexigenic signals, or signals that reduce food intake. Proopiomelanocortin can give rise, among other peptides, to α-MSH, which participates in pathways associated with satiety.

Both systems receive information about the body's energy state and help adjust our behaviour accordingly.

There is no single hunger centre.

There is a network.

Hormones. The gut. Adipose tissue. The vagus nerve. The hypothalamus. The cortex. Memory. Reward. Emotion. Learning. Context.

All happening at once.

So, can we control hunger?

Perhaps that is not quite the right question.

Because speaking about control can make us imagine a battle between ourselves and our body.

And our body is not the enemy.

Our brain is prepared to seek food not only because we need energy, but also because eating can provide pleasure and because we learn to associate certain stimuli, moments and emotions with food.

Understanding this does not mean that our decisions are predetermined.

It means we can begin to observe them from a different place.

We can ask ourselves:

Am I physically hungry?

Am I responding to a habit?

Did the desire appear because I saw the food?

Am I looking for energy, pleasure, calm, distraction, company?

Not to monitor every bite.

Not to turn eating into another form of self-demand.

But to understand ourselves.

Because perhaps one of the most interesting things neuroscience teaches us is that behind many of the behaviours we judge, there is a mechanism that deserves to be understood first.

Understanding before judging

Understanding the brain mechanisms that regulate our eating behaviour can help us make more conscious decisions, but it can also do something perhaps even more important:

change the way we look at ourselves.

It is not only about what we eat.

It is also about why we eat.

The more we understand our brain, our body, our habits and our responses, the more space can appear between impulse and decision.

And perhaps a different way of seeing ourselves can emerge too.

A gaze with less judgement.

More curiosity.

More understanding.

And perhaps a little more love.

Because eating is not simply about meeting a biological need.

It is something we do every day. Several times a day. Throughout our entire lives.

And each time, there is a quiet conversation taking place between our brain, our body, our history and the world around us.

Perhaps conscious eating does not begin with learning how to control the body, but with learning how to listen to it.

Understanding does not mean controlling every signal.

It means being able to choose with greater knowledge.

And sometimes, simply understanding why we feel what we feel can already change the way we experience it.

Eating can be a daily opportunity to nourish the body.

But also to know it.

To listen to it.

And to remember that caring for our relationship with food is, in some ways, another way of caring for our relationship with ourselves.