Why you get tired from bad food

I have been trying to understand insulin resistance for quite a while. All i read gave some clues but no real understanding. Lately I have been following a blog (hyperlipid) which i very detailed about it and one of the latests posts there seem to give an answer. It would seem that overloading your cells with glucose actually make them cut down on the number of mitochondria. That cant be good. And it might explain why i always seemed to get tired for no reason until i changed my diet.  More later