What you gotta remember about Pros is that they walk around much heavier than the weight the fight at. They'll go into training and shed a couple of pounds and then dry up before the weigh in, from starting training to getting weighed the probably loose over s stone, but they put it straight back on afterwards.

Joe Calzaghe fights at 12 stone but walks around at over 13 stone. Your body will be OK doing it for say a month and one fight, but in the amatuers you fight a couple of times a month so you can't dry up, cos if you do, you have to stay at that weight all season.