During the commentary of the Maidana/Broner fight it was said that Broner had gone up to 159 lbs and Maidana to 161 lbs. That was between the weigh-in and the actual fight, which is over 11 stone. The same weight of two middle weights. What kind of food would two guys eat going into a big fight in order to put on so much weight in such short time?
Majority is water weight. They are close to dehydration on weigh in. But also as they are having extremely small meals the couple weeks prior to weigh in, and after the weigh in you can expect a high carb/protein set of meals. Since their body has not been fed their body will store that food as it thinks it's not going to get fed! Hence the weirdly high fight night weights. Surprising how much fighters gain though!!