Complex sentence: The paleolithic diet (also called the paleo diet, caveman diet or stone-age diet) is a fad diet based mainly on foods presumed to be available to paleolithic humans.
Split into simpler sentences: The paleolithic diet (also called the paleo diet, caveman diet or stone-age diet) is a fad diet based mainly on foods similar to those supposedly available to early humans in prehistoric times. It is based on foods presumed to be available to paleolithic humans.