Help, I've got 2 male cats; the oldest has been loosing a lot of weight?

Winn-Dixie was almost 2 y/o when we got Charlie as a baby. They are now almost 3 and 1.5 y/o. Until very recently, Winn-Dixie was the dominant cat. However, Charlie loves to play and seems to always be harring Winn. Not all the time, and not aggressively, but does harr him (usually playing hide & seek). My concern is this, Winn has lost lots of weight since Charlie became the dominant male. Winn doesn't look sick, there don't appear to be any changes in his eating/drinking patterns, he plays along with Charlie most of the time, and can easily get away from Charlie, if he wants (the house is 3,000+ sq ft). . . I don't know if it's because he's just getting bigger, but I'm afraid he's sick. Should I be worried? Or wait & see if other symptoms appear?