Adding fiber to your diet will help alleviate stomachaches and keep your digestive system healthy. One study of fiber's effect on the tummy discovered that people who ate fiber-rich foods at the first sign of a tummy ache cut their chances of getting a full-blown upset stomach in half. If you haven't been eating much fiber, be sure to start slowly. Jumping in with loads of fiber-rich foods after living on burgers and fries will give you a mean case of gas. Add fiber gradually over a few months and drink plenty of water to avoid overloading your system. To get started, grab an apple and nosh away, but remember to eat the peel -- that's where you get most of your roughage.