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In reply to the discussion: Red meat plays vital role in diets, claims expert in fightback against veganism [View all]hunter
(38,302 posts)A meat eater is going to get gassy if they switch suddenly to a rice-and-beans diet.
A vegan who switches suddenly to a meat diet is going to spend many unhappy hours on the toilet.
There are only a few exceptions that involve genetics. Lactose intolerance can be one.
My wife doesn't tolerate milk partly because her Native American ancestors didn't drink milk. As with most humans, indeed most mammals, it was of no benefit and energetically wasteful to maintain the ability to digest lactose into adulthood.
My ancestors drank milk as adults, but milk still disagrees with me. That's because I quit drinking it more than forty years ago. The microbiota in my gut are no longer adapted to milk. But lactase production is merely on standby, it's not shut down. I could gradually accustom myself to drinking milk again.
Humans are a young species. Most of our genetic differences are insignificant in the modern world except as we choose make them so.