If we're going to grant that humans have free will at all (which is debatable, but still, everything works better if we do choose - heh - to make this assumption), then we have to grant that humans are able to choose whether or not to put any given item of food into their mouths and swallow it.

Note that I'm not arguing about whether we "struggle with" weight control or not. Some people absolutely do feel hungrier than others while maintaining the same daily energy balance. But the choice of how to handle that hunger, to keep overeating when you know you are already overweight, or to stop eating even though you still feel hungry, absolutely is something that an individual can control.