Why too much body fat is bad for you

Fat cells get bigger when you gain weight and smaller when you lose weight. But the number of cells stays about the same.

Your fat cells are designed to store fat. When cells become full, the fat ends up in the wrong places, such as our muscles or liver, and that's when we can suffer from diseases such as type 2 diabetes. 

Our fat cells can expand to different sizes depending on our genes, meaning that health varies depending on ethnicity. If you go past your safe fat-carrying capacity, you will get ill.