Why we must be carnivores

I’m reading the chapter in my book, Trick And Treat – how ‘healthy eating’ is making us ill by Barry Groves about why we must be carnivores.  Basically, we have small digestive systems and large brains.  We are designed for an energy dense diet such as is found in fatty meats.  Fossil evidence indicates that our prehistoric ancestors ate very little if any vegetable matter.  They analyzed fossil poop to determine that.  Vegetarians like to compare us to other primates, but our digestive systems are very different from theirs.  Our digestive systems are more like those of carnivorous species.