They had a group of volunteers eat raw fruit and vegetables like the apes do for two weeks. All of them lost weight because none of them could get enough nutrition from the ancient diet. Many of them could not get through the required quantities, either!

It turns out our teeth are shaped wrong and our gut is too small for a diet of raw fruit and vegetables. Our teeth are shaped for mincing and pulping cooked food.

They also had an artifical stomach for experimenting with how ours processed different foods. Raw food was much harder to process than cooked food. I've already mentioned the brief experiment in what happens to food as it is cooked: it destroys the structures we can't digest so we can get to the nutrients locked inside.

Wade.