Actually there is cold hard data to support a calorie restricted diet. Lots of it.
The data was collected on animals, not people. Most results from animal testing don't apply to human beings and vice-versa. Different systems. The feeding studies done on animals have never been done to the same extent with people. You can't lock a human being in a cage and control all their inputs for a life time. Google on CRON. They have a yahoo group. Talk to them, they will tell you the same thing. They believe they are making an educated gamble.
This is mostly true, but some animal studies (although I am against them morally) do have scientific merit. There are many ways we are dissimiliar from the other animals, but there are also many ways in which we are very similar. We all need air, food, water, etc. Lab rats have been chosen because they are cheap and a reasonable approximation to humans. Again, it's not something I support, but it does have scientific value....