Any sudden change to the diet causes digestive problems, <img src="/images/graemlins/frown.gif" alt="" /> especially if the new food is highly refined flour, etc. (like pizza). It is a good idea to think of some additions to the proposed diet which contain fiber.
I would recomend adding some lentils to the stores, they store indefinately and help with peristaltic action. They taste great with spices and go well as an addition to most foods. <img src="/images/graemlins/smile.gif" alt="" />