Janet Jackson learned a valuable lesson from pal Luther Vandross' death - you can't gain and lose massive amounts of weight. Like tragic Vandross, the NASTY singer has battled weight problems throughout her career, often stunning fans with her toned image just months after appearing flabby and out of shape. But Jackson insists her diets are always safe, carefully planned and combined with exercise programmes. She says, "I think part of why Luther had a stroke was because there was so much weight, like 100 pounds, and he would fast. "His system couldn't take it. People think they can skip working out if they can find other ways to lose weight, but you still have to be physically fit, treat your muscles properly."