The fattymouse on the left has a lot of adipose tissue. In many animals, adipose tissue is used to store energy. For comparison, a mouse with a normal amount of adipose tissue is shown on the right
Fat is one of the three main types of macronutrients.[1] Fats are found in many foods. They are made of macromolecules called lipids. Lipids are based on long-chain fatty acids. Some of these are essential because the body cannot make them.