There is an upper limit to protein consumption in humans of about 39% of calories.  After this amount, the excess protein turns into sugar, generating toxins in the process.  This results in "rabbit starvation" which has been discussed several times on this list.
 
Mathematically, animal fat is the #1 statistical variable in longevity (see article sent by Dr. Eades).  From 1850 to the present, the rail;road and then refrigeration have added about 25 years to life expectancy.  As the price of animal fat fell because of these inventions, lifespans increased in mathematical lockstep.  During this same period, modern medicine has added less than 5 years to average lifespans.
 
Vegetarians have not seen these same gains - Steve Jobs died at almost the exact average lifespan of a male vegetarian with access to modern medicine ( 58.6 years).
Vegetarianism was invented in India about 450 BC when populations densities made it difficult to support unproductive old people.  As birth control was several thousand years away, death control was their only option to reduce the incidence of famine.  Those few men that made it to old age (Sadus) were then put on the street with begging bowls to fend for themselves.
 
Ray Audette
NeanderThin