What is hunger?
Oxford dictionary-speaking, hunger is defined as a ‘feeling of discomfort or weakness caused by lack of food, coupled with the desire to eat’.
Hunger is our bodies' response to eating less than normal, or spending more calories than we’ve consumed in the day, which causes changes in the levels of hormones and nutrients in the blood.
Hunger can also be a side effect of the foods you have eaten – more about that later.
How does my body know it’s hungry?
As we mentioned earlier, feelings of hunger are caused by hormone fluctuations. There are two main hormones that affect your appetite:
How does ghrelin work?
Ghrelin is a type of peptide (protein) hormone produced mainly by your digestive tract. It works by signalling to your brain when you are hungry to help regulate appetite, as well as your body’s distribution and rate of use of energy supplies.
When your stomach is empty, ghrelin is released, signalling you to eat. Once your stomach is stretched (due to eating), its production is halted.
Researchers have suggested that ghrelin plays a role in determining how quickly hunger comes back after we eat. Normally, ghrelin levels go up dramatically before you eat and decrease for around three hours after a meal, before starting to rise again.
How does leptin work?
Leptin is a type of adipose (fat) hormone that helps to regulate energy balance by surprising hunger. Leptin travels through the bloodstream by binding itself to proteins.
Leptin helps to reduce your appetite and signals that you have eaten enough to sustain your energy supplies, causing you to feel full.
Your body constantly produces both hormones. In fact, the only time it stops is when your brain releases the stress hormone cortisol. That ‘fight-or-flight’ response causes your digestive tract to stop completely producing a ‘butterfly’ sensation, or speeds it up to the point that you feel sick. Leptin is opposed by the actions of ghrelin, and vice versa.
What about snacks?
But while the science of how our bodies know we’re hungry might make sense, it doesn’t explain the irresistible appeal of snacking between meals – hunger is much more complicated than that.
There are in fact two types of hunger:
- Homeostatic hunger
- Hedonic hunger
Homeostatic hunger is driven by a complex series of signals between body and brain, and signals to our body when we need food to boost our energy supplies.
Hedonic hunger is defined as ‘wanting to eat, dwelling on food or maybe craving something’, and makes use of opportunities to gather extra energy – aka: our eyes detect something that we have previously enjoyed eating and notify our brain.
Hedonic hunger is less well understood than homeostatic hunger, but is thought to stem from a predisposition to foods such as sweets, cakes, biscuits and other sugary, fatty and carby foods, thanks to their wide availability.