I am so interested in what others have said to you about this because I have always suffered from the same thing as well.
It's all the time... and like I saw you mention, I always feel I have contracted food poisoning. I still eat enough but it gets in the way. I only eat bland things, never meat because of it. And yet, I STILL worry just as much.
I just had this problem last night... and at the end of this past week were the most recent times.
What I tried to do was CONCENTRATE on my stomach and try and "find" myself there and I realized I wasn't sick to my stomach at all.. and it was only the chemicals in my body from the anxiety. I did find a little bit of comfort in that.
I am calling my doctor on Monday and going to find a therapist. I think between a therapist and the support here this can be cured.
As I'm reading some responses, as others have said about being hungry and it making you feel sick, I feel that way a LOT in the past month! I hate it!