The Paleo diet

Simply put, the idea behind this diet is that our digestive system was perfected (by evolution) for over 2 million years to function best with the lifestyle of the caveman. That is with rather long breaks between meals, intensive physical effort, lots of sleeping and a diet based on meat, fish, veggies, fruit, roots and nuts that were available at the time. The diet promotes eating whole, unprocessed foods but no grains and no dairy.

Read more at Wikipedia or google "paleo diet".