The work of Dr. Rick Johnson is perhaps relevant. He links the effects of fructose on the mitochondria, which then affects the neurons in the brain, over time.

This hypothesis makes much more sense to me when you think to the associated diseases (diabetes, heart disease etc...)

You can get a overview of his research on this podcast (approx 75min): https://www.youtube.com/watch?v=59Oje6n2JLU