It seems to me that the effect of food on the body has been studied for at least 50 years. No matter how complicated it is, shouldn't there be a few basic thin

It seems to me that the effect of food on the body has been studied for at least 50 years. No matter how complicated it is, shouldn't there be a few basic things everyone can agree on? It seems that each new diet (based on scientific principles) contradicts the last. Low fat, low carb, low calorie, vegan, no dairy, no wheat... They can't even agree on whether a calorie matters. (i.e. is eating 100 calories of steak vs eating 100 calories of sugar the same?)