Image of person eating cake with icing all over their face

The science of being hungry

Appetite involves the brain, stomach and hormones

“Anyone for seconds?” Your answer will depend on how tasty the first helping was, who is asking, and whether you might look ungrateful. Unconsciously, a shifting network of interactions between brain, stomach and hormones will also influence whether you still feel peckish or are completely stuffed.

Many controls on appetite affect a small part of the brain known as the hypothalamus. It responds to hormones produced by the stomach to drive hunger. Ghrelin, which is secreted when no food has arrived for a while, stimulates the hypothalamus to make you feel hungry. The secretion eases up as your stomach fills. The hypothalamus registers many other chemical signals that may tell you to eat less, as well as producing hormones of its own. It is a system with checks and balances.

There is increasing evidence that it can keep your weight fairly constant by making you hungrier if you cut your energy intake – bad news for dieters. Disruption to the appetite system helps us understand how it works. For example, one of the genetic changes in the inherited disorder Prader–Willi syndrome leads to very high ghrelin production, and children with the condition are hungry all the time.

Diagram of a person showing the various influences upon appetite

A. Limbic system: Responsible for memory and emotions. Processes information about previous experiences with food and reward. Could encourage someone to eat more or less.
B. Hypothalamus: Processes signals from gut hormones and fat, and sends its own signals. These include agouti-related protein, MCH and NPY, which block pain signals, give a calming effect and stimulate feeding. There are also other signals, such as MSH, which suppress appetite. The balance of all of these will determine a person’s appetite.
C. Vagal afferents nerve: Sends messages from the gut to the brain stem.
D. Your genes: Can affect how any of these hormones work – a variation could alter a person’s appetite to eat more or less.
E. Stomach: Secretes hormones like ghrelin, which tells you that you are hungry.
F. Pancreas: Secretes several hormones, including insulin, incretins and amylin, which tell you to eat less.
G. Duodenum: Part of the intestines that produces GLP1 and CCK, which send signals that tell you to eat less.
H. Intestines: Secrete a hormone called PYY 3-36, which tells the hypothalamus to suppress appetite.
I. Fat tissue: Secretes leptin, a powerful hormone that acts on the hypothalamus and is responsible for long-term inhibition of food intake.
J. Environmental factors: Increased marketing and availability of food, particularly high-calorie, processed foods.

CC BY

‘Big Picture: Food and Diet’ (2011)

Lead image:

Photo and Share CC/Flickr CC BY

References

About this resource

This resource was first published in ‘Food and Diet’ in June 2011 and reviewed and updated in August 2016.

Topic:
Physiology
Issue:
Food and Diet
Education levels:
16–19, Continuing professional development