En quelques mots

"The production of nervous force is directly connected with the diet of an individual, and its refining depends on the very purity of this diet, allied to appropriate breathing exercises.

The diet most calculated to act effectively on the nervous force is that which contains the least quantity of animal matter; therefore the Pythagorean diet, in this connection, is the most suitable.

...

The main object was to avoid introducing into the organism what Descartes called 'animal spirits'. Thus, all animals that had to serve for the nourishment of the priests were slaughtered according to special rites, they were not murdered, as is the case nowadays".