I'm not sure about his diet scheme/philosophy, but from what I've read about his training methodology he utilizes a 3-week training cycle and manipulates the exercises, weights, sets, reps, and intensity methods across those 3 weeks.
Week 1 is mostly basic, compound movements using heavy weight and reps in the 6-10 range. Week 2 is a mix of compound and isolation movements with reps in the 12-18 range. Week 3 is also a mix of compound and isolation movements but the reps are extremely high and he also incorporates intensity techniques like super sets, drop sets, triple drop sets, giant sets, isometric holds,etc.
His believes in training that targets both myofibrillar growth and sarcoplasmic growth; he believes in training that targets the various energy systems, and he believes in training that targets the various muscle fiber types.
He actually has a really good ebook available describing his methodologies in greater detail. It's called Y3T Method or Y3T Official Guide to Training.
Hope this helps!