I can't say I know if vegetarianism is more or less healthy than being an omnivore, but I feel pretty confident in saying that we won't find the key to health in slavishly attempting to copy the habits of people who weren't anywhere near as healthy as we are.
Pre-historic humans, for example, had a life expectancy of about 30.
One straight forward example of what paleopathologists have learned from skeletons concerns historical changes in height. Skeletons from Greece and Turkey show that the average height of hunger-gatherers toward the end of the ice ages was a generous 5' 9'' for men, 5' 5'' for women. With the adoption of agriculture, height crashed, and by 3000 B. C. had reached a low of only 5' 3'' for men, 5' for women. By classical times heights were very slowly on the rise again, but modern Greeks and Turks have still not regained the average height of their distant ancestors.
Another example of paleopathology at work is the study of Indian skeletons from burial mounds in the Illinois and Ohio river valleys. At Dickson Mounds, located near the confluence of the Spoon and Illinois rivers, archaeologists have excavated some 800 skeletons that paint a picture of the health changes that occurred when a hunter-gatherer culture gave way to intensive maize farming around A. D. 1150. Studies by George Armelagos and his colleagues then at the University of Massachusetts show these early farmers paid a price for their new-found livelihood. Compared to the hunter-gatherers who preceded them, the farmers had a nearly 50 per cent increase in enamel defects indicative of malnutrition, a fourfold increase in iron-deficiency anemia (evidenced by a bone condition called porotic hyperostosis), a theefold rise in bone lesions reflecting infectious disease in general, and an increase in degenerative conditions of the spine, probably reflecting a lot of hard physical labor. "Life expectancy at birth in the pre-agricultural community was bout twenty-six years," says Armelagos, "but in the post-agricultural community it was nineteen years. So these episodes of nutritional stress and infectious disease were seriously affecting their ability to survive."
There are some life expectancy-related habits of pre-historic humans that no-one is aiming to copy - e.g. attacks from wild animals, frequent warfare with neighbouring tribes, lack of sanitation and lack of modern medicine including antibiotics, anaesthetics, midwifery and general understanding of germ theory.
Pre-historic humans, for example, had a life expectancy of about 30.