How does the body know how many calories are in the food it just ate?

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How does the body know how many calories are in the food it just ate?

In: Biology

Well, it doesn’t keep track of the number. But it has a system that tries to extract as much energy from the food you ate, turning the excess energy into fat, and the food that doesn’t get converted into energy, instead gets converted into waste. There isn’t a counter that goes “YOU HAVE EATEN 2000 CALORIES”, but your body is built to take the food you eat and make into the energy you need to live.

It doesn’t work that way. It doesn’t matter if you ate 500 calories or 5000. You’ll use as much as you need for energy and the rest will get stored as fat.

The “energy” food gives you is determined by how many molecules of glucose and in the end, ATP (the body’s energy currency) can be created by the chemical reactions in your digestive tract that break down the compounds in the food you ate. Some molecules like fats allow the body’s enzymes to create more of the compounds needed for triggering other chemical reactions in the body (e.g. powering muscle contractions and transmitting signals over the nervous system). Other molecules, like cellulose, cannot be broken down far enough (by humans, at least) to gain useful compounds from it. This also explains why humans can’t feed on grass while other animals can; they have the necessary enzymes to digest and create energy from grass. The amount of kilocalories listed on the back of a box is by no means an objective amount, it is measured by a scientific method that can loosely be described as burning the food and measuring how much heat is produced, which is of course no accurate representation of how the human body digests food. There is no way to predict how many calories you as an individual will receive from eating food X or Y. All we have is a ballpark.