From the book Food for the Spirit, Vegetarianism in the World Religions:
"Many nutritionists, biologists and physiologists offer convincing evidence that humans are in fact not meant to eat flesh.
Physiologically, people are more akin to plant-eaters, foragers and grazers, such as monkeys, elephants and cows, than to carnivora such as dogs, tigers and leopards.
For example, carnivora do not sweat through their skin; body heat is controlled by rapid breathing and extrusion of the tongue. Vegetarian animals, on the other hand, have sweat pores for heat control and the elimination of impurities.
Carnivora have long teeth and claws for holding and killing prey; vegetarian animals have short teeth and no claws.
The saliva of carnivora contains no ptyalin and cannot predigest starches; that of vegetarian animals contains ptyalin for the predigestion of starches.
Flesh-eating animals secrete large quantities of hydrochloric acid to help dissolve bones; vegetarian animals secrete little hydrochloric acid.
The jaws of carnivora only open in an up and down motion; those of vegetarian animals also move sideways for additional kinds of chewing.
Carnivora must lap liquids (like a cat); vegetarian animals take liquids in by suction through the teeth.
There are many such comparisons, and in each case humans fit the vegetarian physiognomy. From a strictly physiological perspective, then, there are strong arguments that humans are not suited to a fleshy diet."