The Jains ate only a vegetarian diet, and a severely constrained one at that due to additional rules.
The Eskimos ate predominantly raw seafood.
The pastoral herders consumed milk and milk products.
In regions with no cows, people not only consumed no milk; over generations they became lactose intolerant
The Kshatriyas ate meat
Those staying in hot regions added more spices to their food.
Those staying in cold climes ate bland food.
And so on. The variety in human diet is astonishing.
Yet, most societies remained healthy. Those who follow a traditional diet continue to remain healthy.
But any society which gets influenced by "western" culture, read "modern western food habits ", again US is the biggest culprit here, loses its health within two generations, in fifty years or so.
Obesity, Diabetes, BP, ADHD, inability to focus, stress... The list of incurable diseases can go on.
The Pharma companies then step in to provide life long medication for these incurable conditions, making huge profits, and ensuring future profits, since the patients only end up getting worse requiring more and more medication
Actually, the term "incurable" is not true. The clue to "curing" these conditions lies in the realisation that these are mostly problems created in the last fifty years or so.
In which case, the answer will dawn by itself.
Provided you are willing to accept the conclusions that common sense tells you must be true.