What is Hunger
Everyone feels hungry sometimes. It’s a loud signal from the body that it wants you to eat something. Our need for food in order to live is a survival mechanism that is designed to make hunger difficult to ignore.
In this month’s blog posts we’ll look at what causes hunger, why we feel hangry and what we can do to stabilise our appetites.
What is Hunger?
The regulation of eating is a complex process influenced by environmental, genetic, and hormonal factors. Appetite and feeding are controlled by two interacting systems: a homeostatic system, which ensures that a person gets enough calories to survive, and a hedonic system, which regulates the pleasure and reward aspects of eating (1).
The balance between energy intake and energy expenditure is under the control of the brain and central nervous system. Messages in the form of hormones and neurotransmitters are constantly being sent between the brain and the gut, the pancreas, the liver and adipose tissue (fat), These messages regulate the sensations of satiety or fullness (1).
When the stomach is empty it contracts; this alerts the brain to the feeling of emptiness leading to the desire to eat something. When you are full the stretch receptors in the stomach tell your brain that you don’t need any more food. A few hours after eating blood sugar levels dip. This is another signal that tells the brain that you need to eat something.
The hypothalamus in the brain maintains homeostasis in the body. It is constantly monitoring and trying to maintain a steady body temperature, blood pressure and blood sugar among other things, in order to keep the body on an even keel. To do this it receives messages from all parts of the body via hormones and neurotransmitters.
The Hormones of Appetite
Ghrelin – known as the hunger hormone, ghrelin is produced by the stomach and activates the hunger receptors in the hypothalamus. Ghrelin also stimulates the production of stomach acid, needed for the digestion of protein. As ghrelin rises, so does hunger. Ghrelin also decreases energy expenditure, and stimulates cortisol release and is involved in sleep, blood sugar control and anxiety.
Leptin – produced in adipose tissue to send signals to indicate that you are full. It also promotes heat production. Leptin resistance can develop meaning fullness signals are no longer recognised.
In short, too much ghrelin will make you eat more and not enough leptin will mean you won’t know when to stop eating.
Cortisol, one of the stress hormones, mobilises glucose to ensure that the body has sufficient energy to respond to an acute stressor. However, chronically elevated cortisol leads to a blunted leptin (satiety) response, increased desire for calorie rich foods, and the accumulation of abdominal fat.
Other hormones involved in appetite control include asprosin, insulin-like peptide 5, insulin, and cholecystokinin.
Feeling angry or irritable when hungry is known as hanger. This may be due to our evolutionary past when feeling aggressive when hungry could have had benefits in terms of getting food. It may also be that the low blood sugar associated with being hungry triggers the release of cortisol and adrenaline – these are released to raise blood sugar levels and may also trigger anger or irritability.
The Hedonic System
Though food consumption serves a homeostatic function, eating can also be a pleasurable experience meaning sometimes we eat even when we are not hungry. Our pleasurable response to food overlaps with the brain’s core reward circuits (as involved in drugs and sex), such as the amygdala, and reward neurotransmitters such as dopamine (1).
Dysregulation of Homeostasis and Reward Systems
Feeding behaviour can be altered if the homeostatic system or the hedonic system become dysregulated. Appetite dysregulation can be found in obesity, depression, anorexia nervosa, bulimia nervosa, and binge eating disorder (1).
So appetite, hunger and eating behaviours are complicated. Even if we don’t fully understand all the mechanisms behind eating and the desire to eat there are some things we can do to help regulate our hunger. See blog posts Dietary Tips for Appetite Control and Lifestyle Tips for Appetite Control for lots of ideas for how to regulate your appetite and improve health.
- 1. Biol Psychiatry. 2017 May 1; 81(9): e73-e75 Eat to Live or Live to Eat? The Neurobiology of Appetite Regulation. Kinasz K et al.