P90X looks like a lot of effort for minimal gain. I think there are easier ways of getting in shape, but it's whatever floats your boat
Martin Berkhan has done a lot of research into intermittant fasting, you can find him at Leangains.com He's a bit of an asshat though
but definitely in shape.
Intermiittant fasting or "skipping breakfast" is suprisingly easy to stick to and may have some benefits that aren't entirely clear yet. What he does do though that makes the most difference is always cover his protein needs and keep an eye on overall calories.
John Berardi who is possibly the most friendly and innofensive face of the fitness industry tried out all of the variants of fasting and wrote it all up in this free book
http://www.precisionnutrition.com/intermittent-fasting