Why do we get sleepy after eating a big meal? The brain and the intestines require the most energy to work properly. When you eat, the brain sends a lot of blood to the intestines to help break down the food and carry the nutrients all over the body. With blood being diverted from the other organs, including the nervous system, the organs slow down and relax. The result is you get sleepy after a big meal. And, it takes a great deal of energy to digest a large meal, particularly if it is high in fats and carbohydrates.