Exercise the key to a lean body To some, saying exercise is the key to a lean body is controversial. However, being lean is more than just about having an absence of fat, it's also about having muscle. If getting in shape was all about dieting, then everyone would aspire to look like concentration camp victims as they have very low body-fat. But they don't, in my experience, people want to look toned, with visible muscle definition. Although diet helps with this, it only helps if one exercis...