The biology of hunger

The feeling is all too familiar: a growling in the pit of your stomach that usually starts around late morning when breakfast is just a memory and lunchtime is still a tiny speck on the horizon. It’s hunger – a feeling that begins with the hormone known as ghrelin. Once your body has finished digesting and using up the energy from your last meal, your blood sugar and insulin levels drop. In response to this, ghrelin is produced in the gut and travels to the brain, letting it know that sustenance is needed. The brain then commands the release of a second hormone called neuropeptide Y, which stimulates appetite.

Learn how your hormones modulate your hungry feelings

Once you have answered the call and filled up on a good meal, your stomach gets to work on digestion. Nerves in your stomach sense stretching that lets your brain know you’re full up. Three other hormones also secreted by your digestive system take messages to the brain: cholecystokinin (CCK), GLP-1 and PYY. CCK helps to improve digestion by slowing down the rate at which food is emptied from the stomach into the small intestine, as well as stimulating the production of molecules that help to break down food. GLP-1 tells the pancreas to release more insulin and also reduces appetite. The hormone PYY is secreted into the bloodstream by the small intestine after eating. It binds to receptors in the brain to make you feel full up.

Once all of the food is digested, the blood sugar and insulin levels drop and ghrelin is produced once more, so the hunger cycle continues.

When the mind takes over….

When our bodies tell us we are hungry, it’s an innate reaction – the hormones in our systems let us know of the need for sustenance. But when our minds get involved, it’s a whole different story. There’s not much nutritional value in a bacon sandwich or a frosted cronut, for example, so it’s not a ‘need’ for a treat, it’s a ‘want’. This is because the very first time you experienced a cronut, the mesolimbic centre of your brain (the region that processes pleasure) lit up, as the fatty, sugary goodness of the treat released chemicals known as opioids that bind with receptors in the brain.

This triggers the release of dopamine, the feel-good hormone that makes us happy. It’s actually the same one that is released when we fall in love! Your brain remembers this response, and is encouraging you to munch on that delicious cronut to repeat the pleasurable feeling.