When I watch professional martial arts fights, I often find myself baffled how fighters that - judging by the looks - share my body composition compete in weight classes that are more than 10 kg below my own weight. I found out that most of this is due to manipulating the amount of water in your body and read about professional middleweight boxers whose difference in weight between weight-in day and the fight the day after could go up as high as 25 pounds.
The downside of this practise is that you take a huge risk: There's of course the acute danger to die of rehydration if you go too far, but even if you survive this process, you could impede your fighting potential because of malnourishment - or because you gorged yourself too hard after making weight.
So, my question is: Assume you are at the exact body composition level (lean body mass and %body fat) you also expect to have at the day of the competition. How much additional weight can you expect to lose by means of fasting, emptying out intestines, losing water, spitting,... safely (*) when
- a) the weight-in is 24 hours before the competition?
- b) the weight-in is 3 hours before the competition?
Do martial arts competitions and weightlifting competitions require different considerations?
(*) by 'safely' I mean 'not significantly impeding your competition capabilities' and with 'not significantly' I mean that the benefits of competing in a lower weight division still outshine the negative effects of the weight cutting process.