A recent study by Oliver Barley et al. looked at how athletes in different sports cut weight and how much weight is typically cut in those sports. It found that weight-cutting in MMA focused more around dehydration than other sports, and that more weight was cut in MMA than in other combat sports.
The study looked at athletes participating in brazilian jiu-jitsu, boxing, judo, MMA, muay thai/kickboxing, taekwondo and wrestling. In total, 637 athletes completed a survey about their weight cutting habits.
Results
The mixed martial artists surveyed were the most extreme weight-cutters by any measure.