Neither of you are correct. Diets are not one size fits all. People need to listen to their body and eat what works best for them. Some people handle certain diets better than others.

The first time I did carnivore I did it for 5 weeks. My cholesterol actually went down but 75% of the time I had diarrhea. Once I introduced fiber, I had normal shits 100% of the time. I tried carnivore 2 more times and had the same result.

I’ve settled on a meat based diet with beans, fruit, and minimal veggies mixed in, and it works for me.

That being said, I’ve never tried, and never will try, a fully plant based diet because it lacks nutrients and doesn’t give you satiety. We need meat to be healthy, but that doesn’t mean everyone should only eat meat.

My hypothesis is that the diet your body responds to is a direct result of where your ancestors are from (i.e., Greek/italian ancestry will respond best to a Mediterranean diet). Idk if this is true, but it would make sense.