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Why the sight of food makes your mouth water – and more

22.5.2024

Translation: Katherine Martin

Glancing at a tasty piece of food is enough to set an entire mechanical process in motion in your body. Before you’ve even taken a bite, a veritable fireworks display of signals is triggered in your brain, gearing up your liver, stomach and intestines for a feast.

When you look at delicious food, your body anticipates it’ll soon have to deal with a meal. As the body gears itself up to make the best possible use of the food, a series of physiological processes are quickly set in motion. This first phase of digestion is called the cephalic phase, which kicks off before the first morsel even reaches your mouth. The process is sparked by the sight or smell of food – or even the mere thought of something delicious.

When your mouth starts watering

The most familiar part of this process is probably increased saliva production (page in German), as we’re able to feel it happening. Saliva’s needed in the mouth in order to break down and pre-digest food as much much as possible. Having more saliva available makes chewed-up food easier to swallow. Your saliva is also where digestive enzymes first appear. These start breaking down food into its basic building blocks while it’s still in your mouth.

Food lights up your brain with dopamine

The sight of food also activates reward systems (article in German) in the brain that are associated with your well-being. The dopamine system in particular plays a central role here. When dopamine is released, it signals to your brain that you’ll feel good when you eat the food. This mechanism has proven advantageous from an evolutionary standpoint because it drives you to search for and consume food. In essence, it stops you from starving to death. However, in today’s world, where there’s an abundance of food available practically everywhere all the time, this mechanism can often become problematic. Overeating and associated health problems such as obesity can be the result.

In the stomach, movement kicks in

Once the brain’s activated, it triggers other reactions (article in German) throughout the body. It stimulates a reflex causing the production of gastric juices. The stomach lining then begins to secrete more stomach acid (hydrochloric acid) as well as digestive enzymes such as pepsin. This prepares the stomach to optimally digest the incoming food. As well as causing gastric juices to be produced, the sight of food prompts increased stomach movements. Stomach muscle contractions increase in order to mix and break down the food more efficiently.

Peristalsis and digestive hormones swing into action in the intestines

It’s not just the stomach muscles that get moving during this process – it’s the smooth muscles of the intestine too. This causes peristalsis (wave-like movements) necessary for transporting food through the digestive tract. Even before the first bite, hormones such as cholecystokinin (CCK) and secretin are also released into the intestine, helping to regulate digestive processes.

Your gut and brain communicate with each other via a variety of pathways when you see food. The intestine, however, also has its own neuronal network, the enteric nervous system. It can react to stimuli such as the sight of food and initiate digestive processes even before signals arrive from the brain.

The liver prepares itself with a mitochondrial boost

The sight of fatty foods stimulates bile production in the liver. Said bile is then stored in the gallbladder. When food enters the body, bile is released into the small intestine, where it supports the digestion of fat.

A study recently published in the journal Science detailed another way in which the liver quickly prepares itself for incoming food. The mitochondria, the mini power plants of your cells, begin to enlarge and divide. This process, known as mitochondrial fragmentation, serves to ramp up energy production in the liver. If this activation mechanism doesn’t happen, for example, due to a mutation, sugar metabolism is impacted. The liver is then less able to handle insulin and can no longer effectively reduce sugar production. As this is similar to how type 2 diabetes works, new scientific findings on these processes could prove useful in developing new drugs in the future.

Header image: Katerina Holmes/Pexels

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Anna Sandner

Senior Editor

Anna.Sandner@galaxus.de

Science editor and biologist. I love animals and am fascinated by plants, their abilities and everything you can do with them. That's why my favourite place is always the outdoors - somewhere in nature, preferably in my wild garden.

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