Nutrition research is extremely difficult and expensive to conduct. You've always got to take anything with a grain of salt and look at the methods. That being said, I think if you take the average american and switched their diet from whatever meat heavy diet they're on now to a plant based diet, they will likely get healthier. Is it from the plants themselvse? the increased fiber means they eat fewer calories? The increase in the quality of their carb intake? More micronutrients? Less protein? Less dietary cholesterol and more plant based sterols? I have no clue.
I do think a balanced diet is good either way, but I think it's easier to eat an unbalanced meat heavy diet than it is to eat an unbalanced plant based diet.
