I could change my mind at a moment's notice, but lately, I have been thinking that some people are just designed to be meat eaters and some more veggy eaters. I was always so perplexed that someone like Taubes did so well on low carb while someone like Dr. Oz did so well on high veggy/grain diet.
I think most people, including all the "experts", would agree that there is a large genetic component involved. We all know people who can seemingly eat huge meals and never gain a pound, and others who seemingly eat sparingly and continually put on more fat.
I believe Taubes' "insulin hypothesis" is a logical explanation for the second condition, but I'm willing to admit it probably isn't the whole answer.
As for the first condition, I don't see any alternative but to admire those folks for their good fortune in inheriting a great metabolism.
For the rest of us in between those extremes, I think we just have to experiment with various programs until we find one that A) works for us, and B) we can stick with.