When I used to eat meat (and a lot of it at that) a pal - who's still omni to this day - pointed out that whenever I loaded up on burgers, I got a little aggro. To prove him wrong, I stopped eating red meat for a month and lo and behold did in fact lose a little of that testy edge, so I stuck with it. Over time I lost the craving for red meat and eventually everything else... good Sashimi was the last meat I craved, and every once in a blue moon I'll have a bite of someone's fresh fish. Like, maybe every 5 or 6 years. Then the craving's gone again. I firmly believe you should eat what you crave provided you're in tune with it and not just operating out of conditioning. Oh, and I also used to weigh 280 way back then (I'm 6'5") and now can keep a svelte 240-250, no problem.

If necessity demanded, such as travel in a place not capable of offering vegetarian options, then I'd eat the local food. If I or my family were starving, just watch me kill the cow. No problem. Thankfully that's not the case tho.
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One thing that puzzles me about veganism: what do you propose for folks like Mongolian nomads whose land is almost entirely useless for agriculture?