Given the usual pattern of medical research there will doubtless be a new study released soon which "proves" the exact opposite.
Margarine is good then bad then good. I have no idea where we are on red wine these days or aspirin.... and I begin to suspect the term "quack" is not yet redundant.
Of course, we could, for a time, end up with the idea that being both fat and thin are both equally bad but what concerns is the width of the band in the middle considered healthy. If any deviation at all from the BMI ideal is bad we are in trouble. If fat and thin are real extremes I can go and have a nice dinner.