I think some people might be better placed to digest red meat, the same as everything else. Most of the world apart from those of western European descent are lactose intolerant. Many have trouble processing gluten. Some scholars think when hominids decided to eat meat it enabled our brains to develop, with the sudden added protein in the diet.
The key to diets is BALANCED. remember, sugars are a very new phenomenon in our diet. How many people find apples sweet? No one anymore as we have too much sugar, and which isn't natural like fructose. Yet give someone poor who lived 200 years ago a mint imperial and they would probably faint from the sugar. Having a steak, chops lamb etc as part of a balanced meal even every few days isn't likely to cause harm. Same for processed food but the least you eat of these the better. I think ancient people lived probably close to a pescatarian diet, 90 percent of animal protein coming from fish and seafood, and 5 percent from bugs and critters (most of the world still consumes insects) and the other 5 from some big ritual hunt to kill a auroch or something. It's easy to correlate when you see most prehistoric sites are located close to the river or coast.
I don't think humans are designed to eat a wholly vegan diet, partly because of vitamin B12 deficiency from eating no animal or dairy products that would happen if vegan foods and cereals were not fortified with the vitamin. It's pretty much only obtainable from animal sources, apart from like eating a pound of legumes a day or something. Beltic probably knows more though