Tis the season to be jolly, and we all suffer from an upset stomach now and again – especially at times of the year like this when overindulgence is often the order of the day.  Although lots of people claim to have allergies to all sorts of foods that they say cause them digestive problems, when do grumbling tummies become a sign of something more than just too much of a good thing? I find out, in this feature for Training Matters magazine.