When DS was small, we were being told not to put children on low fat food diets, as they need all the calories for growth.
IMO, natural foods, be they fat or not, are waay better than anything produced or messed with.
About 5 years ago, I broke my arm. It was in a place that couldnt be cast, so I spent 6 months virtually housebound, cooking kept me sane.
For 6 months, I cooked 'River Cottage' everyday, and didnt get any exercise. Everything I made had cream, butter, fresh veg and good meat in. At the end of the 6 months, I was ! stone lighter!
Obviously, my own experience wasnt a clinical trial or anything, but it definitely opened my eyes!