Cut food with fork and sharp knife - metal in food?
This shouldn't be an issue. 

From a practical perspective you need a fork to hold food in place, without one the food would slide around. You aren't going to get metal in your food if the knife contacts the fork when cutting, no matter how sharp it is, unless your fork is made of a soft metal of some kind. If your fork is that soft it may be leaching into your food anyway whether you use a knife or not, in which case you should replace it with something like stainless steel.