help

Recently at one bowel surgury for bowel obstruction. I have been losing weight also I went to doctor and deitician and they put me on diet also no fiber, no drink one hour before and one hour after eating so as the food will not rush straight through me. Anyway I take prilocec too and still have bouts when I get upset. I think i am gaining again but concerned. Doctor called wanting to see mee. Said test showed I have fecal fat in stool. What can this do to you? to much or to little can what?