Eating is shaped by internal biological signals and external context. AP Psychology emphasizes how ghrelin and leptin help regulate appetite, while environmental cues and social settings can override or amplify those signals.

Hormones that regulate hunger and satiety

Ghrelin: initiating hunger

Ghrelin is released primarily by the stomach and tends to rise before meals and fall after eating.

Diagram contrasting ghrelin and leptin as complementary appetite regulators. It highlights ghrelin’s pre-meal rise that promotes hunger and leptin’s adipose-derived signaling that tends to suppress appetite by acting on the hypothalamus. Source

It acts as a “go” signal that increases the motivation to eat, partly by influencing brain regions involved in appetite regulation (including areas of the hypothalamus) and reward.

Ghrelin helps explain why hunger can feel urgent even when the body has adequate energy stores—its levels reflect short-term meal timing as well as physiological state.

Two time-course plots showing how appetite-related hormones change around meals. The ghrelin curve peaks pre-meal and drops quickly after eating, while leptin shifts more slowly, aligning with its role in longer-term energy-store signaling. Source

Leptin: signalling energy stores and satiety

Leptin is produced by fat (adipose) tissue and generally reflects longer-term energy reserves. When leptin is relatively higher, the brain receives a “sufficient fuel” message that tends to reduce appetite and support satiety (the feeling of fullness that contributes to stopping eating).

Leptin is especially important for understanding why eating regulation is not only about willpower: the body defends energy balance through signalling systems that can push intake up or down.

How hormonal signals guide behaviour (high-utility overview)

Hormones do not “force” eating; they bias attention, motivation, and perceived reward value of food.

• Rising ghrelin can increase:

  • subjective hunger

  • attention to food-related stimuli

  • willingness to start eating

• Higher leptin signalling tends to support:

  • reduced drive to initiate eating

  • greater sensitivity to fullness signals during a meal

• These signals interact with learning and reward, so the same hormonal state can produce different eating behaviour depending on context.

External cues that influence eating

Homeostatic regulation (internal balance) is often challenged by external cues—features of the environment that prompt eating even when energy needs are met.

Food cues: sight, smell, availability, and portioning

Food-related stimuli can trigger cravings and eating through conditioned associations and attentional capture.

• Salient cues that increase eating likelihood include:

  • appealing sights and smells

  • easy availability (food within reach)

  • highly palatable foods (often high in sugar, fat, and salt)

• Portion size and packaging can shift intake because people commonly use “the portion” as a stopping rule rather than internal fullness alone.

• Learned cues (for example, always snacking during a particular activity) can become powerful prompts that compete with leptin-related satiety signals.

Time of day: routines and biological timing

Eating patterns are strongly influenced by time of day, even when physiological need is similar.

• People often eat because it is a “normal” mealtime, reflecting:

  • habitual routines (breakfast/lunch/dinner schedules)

  • environmental time cues (school/work breaks)

• Biological timing processes can make appetite vary across the day, which can shape:

  • when hunger is noticed

  • how strongly food cues are experienced

• Time-based cues can therefore create eating that feels automatic: the clock becomes a trigger for meal initiation.

Social meals: modelling, norms, and shared context

Social settings can increase or decrease eating depending on group norms and the immediate context.

• Social meals influence intake through:

  • modelling (matching others’ pace or amount)

  • implicit norms about what counts as an appropriate portion

  • extended meal duration (more opportunity to continue eating)

• Social context can also alter food choices (not just quantity), as people may select foods that fit the setting (e.g., celebratory foods) regardless of internal hunger.

• Importantly, social eating effects can occur even when leptin-related satiety would otherwise support stopping, showing how external cues can override internal signals.

Putting hormones and cues together (what AP expects you to do)

For AP Psychology, be ready to connect internal and external influences:

• Ghrelin and leptin help explain baseline shifts in hunger and fullness.

• Food cues, time of day, and social meals help explain why people eat beyond (or sometimes below) physiological needs.

• Eating behaviour is best understood as an interaction: internal signals set the sensitivity to food, while the environment shapes when and how that sensitivity turns into actual eating.