Always hungry? Never hungry? Here’s how the body regulates hunger, and what can change your appetite

Are you hungry all the time even after you’ve just eaten? Appetite is a piece of a complex process in the body that regulates what food you eat and how much of it you eat, as well as how your body uses the nutrients.

Let’s explore body chemicals and other factors that control hunger and metabolism, what can disrupt the process, and when to get medical care.

What is appetite?

Appetite is the subjective desire to eat. It drives what and how much you eat, which is necessary for survival. Your appetite is influenced by your environment, brain processes and dietary factors.

Hunger, satiation (how full you feel after eating) and satiety (how full you feel between meals) make up the phases of the food intake cycle.

Hunger: the body’s signal that you need food. The response can be psychological, associated with the subjective motivation to eat.

Satiation: the sensation of fullness after eating.

Satiety: the degree of satisfaction and/or fullness after eating, preventing further motivation to eat before you’re hungry again.

Hyperphagia: the feeling of extreme, insatiable hunger; a symptom of certain health conditions that need medical treatment.

What environmental factors affect hunger?

Things in your environmental that affect your level of hunger include your individual factors, your social environment, your physical environment and what we call “macro-level” environments. These can all affect what, when and how much we eat.

Individual factors: attitudes, preferences, knowledge, values, behaviors, lifestyle and factors that are biological or demographic (e.g., income, race/ ethnicity).

Social environment: interactions with family, friends, peers and others in your community, impacting food intake through role modeling, social norms and social support.

Physical environment: settings where people eat (e.g., home, school, work, restaurants) or get food (e.g., grocery stores), impacting food intake through access and availability.

Macro-level environment: socioeconomic status, societal and cultural norms; food marketing; food assistance programs; and food and agriculture policy, impacting food intake and choices through legislation, regulation or policies.

The processes that control appetite in the body

Every person has different biological drives for day-to-day food intake, controlled by different organs and tissues that communicate information about your current energy balance to the central nervous system, which ultimately controls this process.

The drive for eating depends on conscious and unconscious processes. Some of these come from your body looking for certain nutrients, and others come from the surrounding environment and your senses.

What we call “homeostatic” and “hedonic” pathways are closely linked with these processes in the body.

Homeostatic appetite control

Homeostatic appetite control involves communication between the brain and other parts of the body. The brain, gut, pancreas, liver and adipose (fat) tissue produce hormones, peptides and neurotransmitters (chemical messengers) that all affect how much of an appetite you have.

For instance, when the gut has no food, it stimulates hunger signals and increases food intake. When there is food in the gut, it signals satiety to stop eating.

Together, those signals and the actions you take can regulate your energy and metabolism in the body. If these signals are dysregulated, though, it can lead to extreme weight changes along with metabolic disorders.

Other things that can influence weight changes and metabolism include activity levels, stress levels, sleep quality, thyroid function and genetic conditions. Hormonal changes (e.g., premenstrual syndrome), emotional state and brain injury can also affect appetite and food cravings, which can lead to weight changes.

Hedonic appetite control

Hedonic aspects of foods are often learned and specific to the senses — sight, smell, taste. They give people their individual preferences, which are more conscious choices. This response ignores the body’s energy status and the nutritional value of the food. The hedonic aspect of food intake can also be affected by appetite hormones in the gut such as ghrelin, which are released unconsciously. Ultimately, though, these preferences are what contribute to food choices that are based on taste or enjoyment rather than on what might be most healthy for us.

How hormones like GLP-1 regulate energy and metabolism

The gut sends nutrient and hormonal signals through the vagus nerve to the brainstem.

Ghrelin: mainly produced and released by the stomach. Before eating and in periods of fasting, ghrelin levels rise, and they lower after eating.

Levels of ghrelin are lower in people who have obesity, prediabetes and diabetes. High levels of ghrelin are seen in Prader-Willi syndrome (a rare genetic condition). Levels of ghrelin are also higher when someone has low blood sugar, a lack of sleep or disrupted circadian rhythm.

Other gut hormones signal satiety through the hypothalamus and other brain areas.

GLP-1: released from the intestine after direct contact with carbohydrates, protein and fat.

PYY and CCK: released after contact with protein and fat in meals. Their release leads to slower stomach-emptying and food intake.

Levels of GLP-1 and PYY are low in obesity, prediabetes and diabetes.

Leptin: one of the adipokines that adipose tissue (body fat) releases. It’s a marker of long-term energy stores to help maintain body weight, and the less body fat you have, the less circulating leptin you have. Leptin signals satiety, and its levels decline during fasting, making you feel hungrier.

Low levels of leptin can suggest congenital leptin deficiency, leading to extreme hunger, obesity and low sex hormone levels. Conditions associated with high levels of leptin include obesity, nonalcoholic fatty liver disease, neurodegenerative disorders, depression and food addiction.

Insulin: released from the pancreas in response to changes in energy stores. Like leptin, insulin levels are proportional to body fat. High levels of insulin decrease food intake, and lower levels increase food intake. It’s important for regulating blood sugar levels and storing blood sugar and fat. High blood sugar levels often result in greater hunger and cravings.

Unlike leptin, circulating insulin levels are closely related to visceral fat (belly deep in the abdominal cavity) than subcutaneous fat (stored beneath the skin). Conditions associated with high levels of insulin include obesity, metabolic syndrome and polycystic ovary syndrome.

How your diet can affect your appetite

The ways we take in energy and nutrients play important roles in our gut and appetite. Certain amounts of energy are needed for the brain and body to function properly. Brain tissue is made up of nutrients, and diet gives our body what it needs to produce those hormones, peptides and neurotransmitters.

In the brain, glucose, amino acids (building blocks of protein), and lipids (fats) are important components of cellular function because of how they help the body communicate its needs with appetite, storing energy and regulating food intake. When these lines of communication are disrupted, it can lead to obesity or undernourishment.

Diet factors that can disrupt those appetite signals and drive hunger, promote increased food intake and cause weight gain:

• Undereating
• Diets low in fiber, protein and healthy fats (monounsaturated fats, omega-3 and omega-6 polyunsaturated fats)
• Diets high in refined carbohydrates, added sugars, sodium and unhealthy fats (saturated and trans fat)
• Irregular eating patterns, including frequency, spacing, timing and skipping of meals
• Nutritionally imbalanced meals
• Not drinking enough water
• Alcohol use

Eating quickly has also been suggested to cause a weaker response in appetite-suppressing gut hormones.

Medications that can affect appetite

Certain medications can also affect appetite and lead to weight changes. These include:

• Antihistamines
• Highly active antiretroviral therapy
• Some antidepressants, mood stabilizers and antipsychotics
• Some beta-blockers
• Some diabetes medications
• Some seizure medications
• Steroids

When to see a health care provider

An increased appetite doesn’t always indicate a problem. But if you notice your increased appetite persists and is accompanied by unintentional weight gain in a short period, talk to your primary care provider about testing, nutritional guidance and treatment options (including alternate medication options if you’re currently prescribed something with a risk of weight changes).