Hi Roadrunner,
Stitches are normally caused by a muscle spasm of the diaphragm. If the body has some trapped air/gas below the diaphragm, or if you start exercising too vigorously or as is more likely in your case if you eat too close to exercise, the diaphragm may cramp causing pain under the rib cage.
As with any muscle cramp, the best immediate treatment is to try to stretch the cramping muscle as much as possible. But how do you get to the diaphragm which is on the inside of your body? Hmmmm several options open to you:
- Try altering your breathing pattern. Take a deep breath in as quickly as you can, to force the diaphragm down. Hold the breath for a couple of seconds and then forcibly exhale through pursed lips to restrict the outward air flow.
- You may also find that bending forward can help you expel as much air as possible. I have actually found that stretching up as tall as I could, even to the point of extending arms up over my head, then alternating crouch-tall and tightening/flexing the abs, helped as well.
- You may even have to stop and walk briskly for a few seconds while concentrating on deep breathing.
If you get a cramp in the middle of a run/race, you might want to try mixing up your rhythmic breathing/ striding pattern. If you always exhale when your right foot strikes the ground, try exhaling with the left foot strike. It does work believe it or not!
The most effective way to prevent a side stitch is to take deep, full "belly breaths" while running. This will allow the diaphragm to fully lower and reduces the stress on it. If you take a lot of shallow breaths when running, the diaphragm remains in a consistently high position and never lowers enough to allow the connective ligaments of the liver to relax. The diaphragm becomes stressed and a "stitch" may result. Another way to prevent stitches is to make sure you include a warm-up that helps you gradually increase your running speed. If you head out in an all-out dash from the front door, you're more likely to take quick, short, shallow breaths, inducing a cramp.
Running in extreme cold temperatures may induce side stitches, as it's less comfortable to take in deep lungs full of frigid air until you're thoroughly warmed up. Try doing some sort of warmup indoors first, before hitting the icy streets.
Strengthening the abdominal and lower back (core) muscles can help prevent stitches since tighter muscles in the mid-section will allow less movement of those internal organs (that's why a lot of sprinters have six packs to die for!).
Hope this helps...
!!! I am really psyched up to run and my body won't let me! I even threw a little paddy in the middle of the street before! 
