Why do we feel hungry?

NARRATOR: Once upon a time, some psychologists took two patients and fed them lunch. Ten minutes or so later, the patients were offered lunch again and happily ate lunch number two. Again, 10 minutes later, the patients were offered lunch, and just as happily ate their third meal. These patients had severe amnesia. They had no recollection of just having a meal. So they were willing to accept all the TV dinners of turkey, peas, potatoes and applesauce.

The question of when and how much you eat has to do with a whole lot more than how much food is in your stomach.

The control group in that study politely declined all of the meals after their first lunch. Memory for what you’ve recently consumed is a big contributor to beginning a meal. Your brain also controls hunger by telling your body when it needs energy. Your brain only takes up about 2 per cent of your body weight, but it chews up 20 per cent of the energy you get from your daily food intake.

Your brain tries to make sure all this energy is even, so that the energy coming into your body through kilojoules you eat is the same as the energy you expend moving around. This is known as energy homeostatis. When your body has a low battery and needs more energy, hormones come from your fat cells, certain organs, and the gastrointestinal tract to tell your brain it’s time for a snack. Inside your brain, the hypothalamus picks up on these peripheral signals and a bunch of appetite-stimulating neurons travel out to tell other areas of your brain that you’re really hungry. And what follows, well, for me anyway, is thoughts about tacos. But sometimes these pathways don’t work the way they should. It’s not just severe memory loss that causes people to eat and eat and eat.

In people who suffer from obesity, these hormones can have trouble travelling into the brain. With a decrease in these hormones in your hypothalamus, your brain thinks your fat cells are decreasing in size, even though they’re not. And the appetite-stimulating neurons still travel out to say ‘eat up’. But this isn’t the case for everyone. It’s rare that this pathway is damaged, and more common that the system is overridden by our desire to eat. Fatty foods have been found to tap the pleasure centre of the brain. When you eat something delicious, like a taco, your reward system lights up and you feel pretty awesome.

But we don’t all win the hunger games. If you eat tacos day after day, the reward response decreases, and you have to eat more and more tacos to experience the same reward. This can lead to a food binge, or cycle of fake hunger. Also, there are other environmental factors that cause us to eat. Overly descriptive names on menus can lead us to eat more because we want to experience more of that product. Cold restaurants lead people to have more food, because you’re expending more energy trying to warm up. And in one study, people kept a diary with reasons why they started eating. ‘I saw the food’, ‘I was bored’, or ‘I wanted to be with other people’.

The next time your stomach rumbles, it could just be your brain telling you that the ‘succulent, slow-roasted grain-fed Aztec-spice hand-pulled organic pork taco’ is exactly what you need to recharge your battery.