Heard about this. The truth is, cutting weight is a part of those sports and if done irresponsibly can really hurt you. However, this isn't that common in comparison to how many folks are doing it all the damn time. It's a sad, sad story, but...
The reason Brazilian fighters seldomly fight outside of their country is because of how lax their drug testing is. Most of those guys are juiced up and would be exposed if they left Brazil. Dude that died, while tragic, might have been doing something he wasn't supposed to do. We'll have to wait for more info.
Cutting weight story:
In the wrestling offseason of my senior year in high school I ballooned to about 132 lbs. Once the season started I was facing a couple options: either I wrestled my natural weight, but have to challenge Keron at 130... or wrestle JV. Knowing I couldn't beat Keron, I dropped. But it didn't stop there. At 125 was Chris Perez (which I could beat, but the coaches urged me to drop more) so down I continued. At 119 was Mike (and this was when Mike was really starting to become good) so down I went to 112, the weight I wrestled the year before. I had lost 20 lbs in just 2 weeks! It was insane. Then I had to keep it down throughout the season. I won regionals and districts before going to state and basically giving up because I was so hungry. True story.