You cook if you’re not too lazy or in a rush. You finish eating – 7:30 am. The rumbling ceases. The pain is a distant memory. You’re full. Your day can begin.
So what just happened? Why was your stomach rumbling? Why did it hurt? Well, that’s redundant – you were hungry! But, who says? Did your stomach tell you or did your brain tell you? Similar to the chicken or the egg paradox, let’s see if we can get one step closer to determining the origin of hunger.
Let’s start with the basics – hormones. Hormones control pretty much everything in your body – how you grow, how excited you are, how sleepy you are, and yes, how hungry you are. The hormone that initiates hunger is called ghrelin, which stimulates appetite. This is produced in the stomach. It tells the brain that it is time to eat. So what about all the rumbling?
The gastrointestinal tract (GI tract) is a system of smooth muscle (meaning you can’t control them consciously) that runs from the mouth to the anus. Peristalsis is the act of the downward contractions of said muscles (how else would you get food into your stomach?). The GI tract is essentially comprised of hollow tubes with gasses and fluids constantly passing through them. When you’re hungry and feel (and hear!) your stomach rumbling, what you are experiencing is the passing of gas and fluids through those hollow tubes when they are empty. That explains the noise as well, doesn’t it?
Back to the hormones! So, ghrelin initiates hunger, and then you eat. Higher ghrelin levels tend to mean you’re hungrier. They are at their highest just before a meal and then subside for about three hours after a meal. What makes ghrelin levels subside? Leptin!
Leptin is a hormone that is produced by adipose tissue (fat). It suppresses appetite. Therefore, having more fat tissue means that there is more leptin circulating. This ultimately suppresses appetite.
Both of these hormones are sent to the hypothalamus, a structure in the brain that acts as a thermostat of sorts. It controls body temperature, hunger, parenting and attachment behaviors, thirst, fatigue, sleep, and several other bodily functions. When a thermostat senses that the temperature deviates in either direction from a certain point, it takes measure to bring it back to where it should be by either heating or cooling the air. The hypothalamus does the same. When ghrelin levels get too high, the hypothalamus signals for leptin to be released and vice versa. This is called homeostasis.
However, it should be noted that hormones, especially ghrelin and leptin, perform a variety of functions. Their complexity doesn’t allow us to fully understand them. Even if we were to fully understand hormones, we would yet be confronted with another obstacle – the brain.
Even the top neurologists in the top cities in the world have difficulty understanding the human brain to the fullest extent. Everything we do, everything we think, everything we feel, all of it, is relayed to and processed by our brain. Although science is getting closer and closer to understanding the brain, we are still only at the tip of the iceberg.
With all of this information taken into account, it seems that the stomach and the brain control hunger independently, but rely on each other at the same time. Your stomach may release the hormone that makes you hungry (ghrelin), but it has to be given the OK by the brain to do so. This superficially simple, yet extremely complex interaction works in harmony with every other system in our body and allows us to live the way we do.