I am tormented by gross thoughts about food that I can't stop and it's interfering with life. How do I stop them?

When I was a kid I found I couldn't leave my bowl of cereal alone or I couldn't eat it. If i was present and watching it I knew nothing bad had happened to it, If i left it for any reason my mind would suggest all the things that could be in there that I couldn't see, typically worms, and I would have difficulty choking it down. As an adult, this has morphed into, i see something i find gross, (worms and house centipedes mostly) the next time I go to eat my mind will give me vivid images of finding, ( or worse, NOT finding) those things in my food to the point where even if i do manage to put the food in my mouth I'm fighting my gag reflex to swallow and keep it there. The result is that I won't/can't eat the rest of the day and only manage light amounts the next. Extreme distraction at the time of eating helps, watching a isn't typically enough but reading a book or very compelling or passionate conversation can. Why does my brain do this to me? Why does it hate me? How do I get it to STOP? I have a very fast metabolism and am already teetering on being underweight.