Tim Ferriss is a very interesting guy. Over a number of years he's managed to reduce the time he spends working (but not necessarily his output) to a tiny 4 hours per week, simply to spend more time pursuing his other interests; chief among them, MMA.
His blog contains an intriguing blend of productivity tips, dietary and fitness information; a great example of which is the piece How to lose 20lb of fat in 30 days.
NB : If you're anything like me, and eat large amounts of bread, rice and pasta on a routine basis, this isn't going to be easy. Sounds like a challenge.