How long can someone go without eating? And if someone does'nt eat for a really long time will they lose a lot of weight just by not eating?

they will lose weight but not that much
about 4 days without food

Yes weight-loss will occur. The person will also experience mood swings, increased thoughts of food, obsessive behaviors. Malnutrition is an obvious health-hazarding side-effect. All bodily systems will shut down. The metabolism (the thing that helps burn of calories) slows down to conserve as much energy as possible, which is stored as fat. Once the body runs out of fat (something that IS essential to the body in HEALTHY amounts), it will start to eat muscles, inculding the heart. The length of time someone can live w/o food varies at most a month maybe.

you will lose muscle weight but not much fat