When your body has extra energy, it stores it in fat cells by making the cells bigger or making more of them.

Even small fat cells can be unhealthy and unable to grow when needed, which might cause problems too.

This is a theory about how fat storage works in the body. It says there's a limit to how much fat subcutaneous fat cells (the fat under your skin) can hold. Once they're full, any extra fat gets stored in more dangerous places like belly fat and the liver.

Scientists don’t know enough about how the whole mix of small and big fat cells works together to affect health.