Eating behavior is partly controlled by chemical signals that communicate the body’s energy needs to the brain. Two key hormones, ghrelin and leptin, help regulate hunger, food intake, and fullness.

Ghrelin and hunger

Ghrelin is a hormone strongly linked to the start of eating.

When the stomach is relatively empty, ghrelin secretion rises. The hormone travels in the bloodstream to brain areas involved in appetite regulation, signaling that the body needs energy. This makes a person feel hungrier and increases the motivation to seek food.

Ghrelin is usually described as a short-term hunger signal because its levels change across the day in relation to meals.

This graph shows how circulating ghrelin changes across a typical day: levels rise before meals (preprandial peaks) and fall after eating (postprandial suppression). It visually supports the idea that ghrelin functions as a short-term signal that helps initiate meals. Source

• Before a meal, ghrelin levels tend to rise.

• After eating, ghrelin levels usually fall.

• This pattern helps explain why hunger often builds up before regular mealtimes.

Ghrelin does not simply create a vague feeling of hunger. It can also increase the rewarding value of food, making eating more likely when food is available. This means ghrelin is especially important in meal initiation.

Leptin and satiety

Leptin works in the opposite direction to ghrelin and helps reduce food intake.

Unlike ghrelin, leptin is not mainly a meal-to-meal hunger signal. Instead, it provides the brain with information about how much stored energy the body has available. When fat stores are larger, more leptin is usually released. Higher leptin levels reduce hunger and make continued eating less likely. When fat stores fall, leptin levels drop, and appetite tends to increase.

Leptin is therefore often described as a long-term satiety signal.

This diagram summarizes leptin’s role as a long-term signal from adipose (fat) tissue to the brain. It highlights that higher fat stores increase leptin release, which acts centrally to reduce appetite and support energy balance over time. Source

It supports the maintenance of a relatively stable body weight by reducing food intake when energy reserves are sufficient. In everyday terms, leptin helps the body avoid unnecessary eating over time, rather than just ending one specific meal.

How ghrelin and leptin work together

Eating behavior is influenced by both hormones acting as part of a feedback system that helps maintain energy balance.

This schematic maps ghrelin and leptin onto key hypothalamic pathways that regulate eating. Ghrelin promotes appetite largely by activating orexigenic NPY/AgRP neurons, while leptin reduces appetite by shifting signaling toward anorexigenic (melanocortin/POMC-related) output. Source

Ghrelin pushes eating upward when energy is needed, while leptin pushes eating downward when energy stores are adequate.

Their combined action can be understood as follows:

• Low immediate energy availability: an empty stomach raises ghrelin, increasing hunger.

• Food is eaten: ghrelin falls, so the drive to continue eating is reduced.

• Body fat levels over time: adipose tissue releases leptin in proportion to stored energy.

• Sufficient energy stores: higher leptin reduces appetite and supports lower intake.

• Reduced energy stores: lower leptin removes some of this inhibition, making eating more likely.

This means hormonal control of eating behavior includes both short-term regulation of when a meal starts and longer-term regulation of how much energy the body wants to store. The system is not perfect, but it helps explain why hunger changes across the day and why appetite can also alter after weight loss or weight gain.

Research evidence

Support for ghrelin

Research has shown that ghrelin levels typically rise before meals and drop afterward. This pattern supports the claim that ghrelin helps trigger eating rather than simply appearing after food has already been consumed. Studies using ghrelin administration have also found increased food intake, suggesting the hormone has a causal role in promoting hunger.

Support for leptin

Leptin research also supports a hormonal explanation of eating behavior. Individuals with very rare leptin deficiency show extreme hunger and excessive eating, and leptin treatment can reduce this. Animal studies have found similar effects, with low leptin linked to overeating. These findings suggest leptin normally acts as a brake on food intake.

Limits of the explanation

However, ghrelin and leptin do not control eating behavior on their own. People may eat because of habit, social situations, food cues, or emotional state even when hormonal signals would not predict eating. In addition, some individuals have high leptin levels but do not show a strong reduction in appetite. This is often described as leptin resistance, where the brain becomes less responsive to leptin’s signal. As a result, the hormonal explanation is important, but it is not a complete account of why people eat.

Why these hormones matter

Changes in ghrelin and leptin can alter eating behavior in predictable ways. After a period of fasting or dieting, ghrelin may rise and leptin may fall. This combination makes food more appealing and can increase the likelihood of overeating once food becomes available. After a period of sustained positive energy balance, leptin should rise and help reduce intake, although this signal may not always be effective.

The key distinction is:

• Ghrelin mainly increases hunger and encourages eating.

• Leptin mainly decreases hunger and limits eating.

• Ghrelin is closely linked to the stomach and current meal patterns.

• Leptin is closely linked to adipose tissue and longer-term energy stores.

Understanding this contrast helps explain how biological processes contribute to the control of eating behavior.