From Loretta Hunt's article on Mousasi:

The decision to move up in divisions was made out of necessity, he says.

"After the tournament, I took a break for 10 days to see my family in Armenia," says Mousasi. "I decided, ‘Let’s put on some weight.’ I just start eating and I didn’t train, and after that, I was 96, 97 kilos [216 pounds]. I gave my body a little bit [of] rest, and my body grow because of my age. I didn’t let my body grow and now it grows naturally. I need to go up."

The growth spurt probably hasn’t thrilled Dream executives, who had just crowned their first-ever middleweight king and a good one at that, but Mousasi says a weight cut at this point would be unhealthy for him.

"They wanted me to defend my belt one more time, but going from 216 to 185, it’s not possible for me anymore," he says. "I have to move up."

Gegard Mousasi has certainly put himself on the map as one of the world's top middleweights, and there are a plethora of potentially great matchups for him at 185.  I'm not sure if "necessity" is the proper term to use in describing the move, but he seems determined to make said move.  Mousasi goes on to explain his ultimate goal:

"To be honest, I want to go to heavyweight," he says. "I think if it’s something you do and you win, people will be surprised, and I like that. It was always my dream to be the best. If you say, ‘I’m the best heavyweight’ it feels like you’re the best heavyweight in the world. If you say, 'I’m the best middleweight,' there’s always a couple of guys above you that could beat you."

If all goes as planned inside his cool but calculated mind, Mousasi will make his U.S. debut at Affliction and M-1 Global’s third event in June or July carrying 225-230 pounds on his frame the natural way.

...

Mousasi has also been influenced by Fedor Emelianenko, who has made his last two appearances in the States and trumped two former UFC champions, Tim Sylvia and Andrei Arlovski, in a combined 3:50. Emelianenko and Mousasi are both managed under the Red Devil International banner and have worked out together.

"Training with him, that’s also one of the reasons I thought I can be a heavyweight," says Mousasi. "Standing next to Fedor, I feel so much bigger than him. When you train with him, he feels like a middleweight. He’s as strong as a heavyweight but as fast as a middleweight, so I think that makes him special. If I can take my speed as a middleweight, have that explosiveness and mobility and move up to heavyweight, I think that’s something a lot of them don’t have."

Mousasi even points to Paul Buentello as a good opponent for him to debut at heavyweight against.  This entire plan is intriguing to say the least.  The current trend in MMA is fighters cutting weight to gain a relative size advantage over their opponents, or at least to avoid the disadvantage of being relatively smaller.  Heavyweight is the extreme scenario with some guys now cutting to get down to 265.  True, Fedor Emelianenko has been dominant as a small heavyweight, but is he a good example or just an anomaly?  If enormous fighters in the mold of Brock Lesnar and Shane Carwin are able to effectively apply their wrestling skills while significantly bettering their overall games, I have to believe that these types of athletes could give even Fedor a stiff test.

Mousasi possesses a multitude of skills as a mixed martial artist, and at 23, he has a lot of time to improve further.  With that said, I'm quite skeptical of the course he has proposed.  Mousasi almost sounds as if he buys into the common misconception that being the best heavyweight fighter is equivalent to being the best fighter overall.  I'd love to see him fight some of the top middleweights and light heavyweights here in North America. Heavyweight, however, presents some unique problems for a man with Mousasi's frame.

Whatever your opinion, one thing seems apparent; Gegard Mousasi is not afraid of a challenge.