Gucci Mane: Silver Lining Prison Playbook

Gucci Mane may have lost his freedom by doing time, but he also lost a ton of weight ... and he'll continue with his prison diet to keep his abs tight and the lbs off.

Gucci dumped 50 pounds behind bars by staying clear of carbs. It helped that he couldn't booze it up. He believes a no-carb diet is the key and he will carry that forward during his house arrest. Interesting ... we can't get a clear answer on whether Gucci will hit the bottle again.

The rapper knows exercise is critical, so he'll continue his prison regimen of sit-ups and weights ... just at a 24 Hour Fitness instead of the yard.

Gucci's so serious about his new physique he turned his nose up to cake and booze for his coming home party ... so says his lawyer, Drew Findling. He stuck to chicken and agua.