It has been known for decades that populations consuming high-protein, meat-based diets have higher cancer rates and lower life-spans (averaging as low as 30 to 40 years), compared to cultures subsisting on low-protein vegetarian diets. Some of these have lifespans of more than 90 years.
Dr. Alexander Leaf published the findings of his research about the oldest people in the world in the January, 1973 edition of National Geographic Magazine. He found that the three most consistently disease-free and long-lived people on Earth are the Abkhazians of Russia, the Vilacabambans of Ecuador and the Hunzukuts of Pakistan. None of these peoples suffer from Western diseases: NO obesity, NO cancer, NO heart disease! On the average these people live to be over 100 years old. The men are physically active and still fathering children at 100 years of age.
The diet of all of these people consists of 70-80 percent high-water-content foods such as raw, uncooked fruits and vegetables. These people eat very little or no animal products.
Meat protein is the most difficult food for the body to digest. The average time for food (other than fruit) to pass through the entire gastrointestinal tract is between 25 and 30 hours. When meat is eaten, that time is more than doubled!
Research published in the New England Journal of Medicine, in September, 1982 states, "undigested protein must be eliminated by the kidneys. This unnecessary work stresses out the kidneys so much that gradually lesions are developed and tissues begin to harden."
In the colon, this excess protein waste putrefies into toxic substances, some of which are absorbed in the bloodstream. The University of Illinois Medical School reports that "A high protein diet also breaks down the pancreas and lowers resistance to cancer as well as contributes to the development of diabetes."