From H. Leon Abrams Your Body is Your Best Doctor:
"Actually, the digestive mechanism of man is adapted to a mixed meat and vegetable diet.
Human teeth consist of three types: canines or piercing teeth of the meat-eating animals, the incisors of plant - eating animals, and the molars of grinders of grain-and-nut eating animals.
With respect to structure, human teeth are conclusive proof that the human body is adapted to a mixed animal and plant diet. Man has specific digestive ferments for meat proteins and other special digestive juices for carbohydrates.
His stomach and intestinal tract is equipped to handle both. Man is naturally adapted to a mixed of diet animal and plant foods."