Eating doesn't give you energy right away, in most cases, and overeating often has energy that doesn't convert quickly.

Potato chips, meat, bread, rice, etc, are calorie dense, but full of complex carbohydrates and fats that need to be broken down into more simple sugars.

That process actually uses energy in the short term, before giving you a boost of energy later.

Simple sugars, like those found in juices and desserts, don't need to be broken down, and provide energy very quickly to the body.

So, what happens when you overeat? Your body shuts down to process the food, then has nowhere to go with the excess energy. That energy is then converted into fats and stored in the body for later.