When I did fruit juice fasting with herbs, I felt better overall, both physically and mentally. My mind felt clearer and I felt more focussed and calm. Of course during cleansing, there were good days and bad days.
I'm not sure of the source of your anxiety or how severe it is. So looking for the root of what is causing it will be important.
What comes to mind is to check into side effects if you're taking any medication. Anxiety can be caused by past experiences or current life situations. Sometimes help from a professional is helpful.