Early humans ate less meat, were more active and died a lot younger than modern humans. Eating less meat and being more active helps mitigate a lot of meat's negative properties and frankly their shorter life-spans meant that they likely died of any number of things before meat-induced heart disease had a chance to kill them.
Considering that meat was calorie and protein dense and the human brain is a very energyintensive organ. It was well-worth the trade to add meat to the diet. But in modern days we have gone way too heavy in meat based diets. It's far in excess of what our bodies need so the negatives start to outweigh the positives.
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