Fat is an obsession, a dirty word, a subject of national handwringing--and, according to biochemist Sylvia Tara, the least-understood part of our body. You may not love your fat, but your body certainly does. In fact, your body is actually endowed with many self-defense measures to hold on to fat. For example, fat can use stem cells to regenerate; increase our appetite if it feels threatened; and use bacteria, genetics, and viruses to expand...