Two things get in most people's way: nutritional knowledge and emotional control.
Health and age is a factor for some ofc but can you honestly say that people know the nutritional value of what they're eating and also can emotionally control when they eat?
This perspective doesn't properly take into account the complex metabolism of the human body, and the psychological complexity of the brain.
The apparent phenomenon of "free will" emerges from a chaotic, dynamic system, but you must understand the underlying variables if you want to effectively manipulate the result of their interactions.
