The two organs in your body that require the most energy to work properly are the brain and the intestines. When you eat, your brain diverts energy towards digestion, sending a bunch of red blood cells over to help break down the food and carry the nutrients all over your body! Because so many blood cells are helping out the intestines, the rest of your body takes this time to slow down and relax. As a result, you might feel tired, since your brain doesn't have as many blood cells to help it out at the moment more energy used for digesting food means less energy can be used for running around!
Further informationWhat you eat can also affect how you feel after. Some foods that are high in carbohydrates, such as pasta or potatoes, are turned into a chemical called "glucose" when they're digested. If your body has too much glucose, it releases a chemical called "insulin" to balance it out. Insulin reacts with a protein in your brain called "tryptophan" to create a chemical called "serotonin," which is the chemical that tells your brain when you should go to sleep! All of these chemicals work with each other, but sometimes your brain gets confused and releases too much serotonin as a result “” it's harmless, you might just need a nap!
Some foods are also high in tryptophan, which has the same result. Turkey and milk are common examples, which is why you may have heard that drinking a glass of milk before bed is supposed to help you get to sleep!