Sweat is Just Fat Crying (some of it anyway).

Fat cells in humans develop primarily during childhood and puberty. After that, the number of fat cells in your body remains relatively stable. These cells make up adipose tissue, and they can send out hormones into the body to help regulate everything from metabolism to body weight.

Because we generally have a set number of these cells, gaining weight doesn't typically involve making more. Instead, individual cells expand as the digestive system breaks down and stores food for later use, then they shrink when the body turns to the fat cell in a moment of need