Low carb or low fat
After all of these decades of so called expert advice it seems they, the experts, don't know. For a while it was carb loading, then get rid of gluten, low fat diets, high protein diets, and a long list that now includes a paleo diet. Who knows? It appears the experts don't agree either.
It is clear that if you subsist on carbs mostly that it usually adds fat to the waistline. Excessive carb intake has many negative effects and conversion to sugar in the system of one of them.
Excessive fat intake has its own worries. This was part of the Atkins diet that was high in fat and protein.
Heavy protein intake also creates issues for many people.
With all of this in mind it seems that a balanced diet still makes sense.