There's the secret.
I'm kidding, non-male members of HN!
On a more serious note: "even though it was “understood that the custom of eating flesh corrupts the body.”
As a vegetarian, I find this intriguing. Why, if it was understood thus, did meat eating become so prevalent?
The source material [0] that the quote is taken from has a footnote that says "The Cistercians held that rich food increases sexual appetite"
It would seem that the "corruption" here is related to keeping ones libido in check.
[0] https://books.google.com/books?id=cBqgOXfMxAoC&pg=PA26&lpg=P...
The problem is that, before modern refrigeration was introduced, it was very easy for meat to go bad and make people ill. This was very common in warm countries, and so it ended up codified in religious cultures from those areas. Around the Med, it was no biggie: vegetables were pretty easy to grow in large quantities.
However, the type of doctrine that ended up as commonplace in Europe (because of military and economic developments) was a very Northern interpretation of Christianity, coming from places where people had to eat meat because vegetables were hard to grow in cold climates. A lot (or rather most) of the Templars themselves were French or German knights; they came from places were meat was a firm staple of rich diets.
And so most of the warnings against meat went out of the window, never to return. It probably helped that "the Enemy" had gone the opposite way.