This thead should be re-titled 'old wives tales for preventing delhi belly'
Personally speaking I would never take the collection of drugs which has been suggested. I think our friend the pharmacist, JonF, offers the best advice when suggesting that we practice basic food hygene.
My organisation offers us basic advice when travelling to certain regions, this is along the lines of never drink the local water or eat anything which may have been washed in the local water without being cooked (salads etc) Also wash your hands thoroughly before and after eating, not all illnesses abroad are in the food. Lastly, and most importantly, be prepared if you do fall ill.