Why does watermelon cause an upset stomach?

Practically everyone: Has some food intolerance, & may include such innocuous ingestants as water (or watermelon). Reference: elaine shimberg, "relief from ibs".Avoid foods that bother you, but best to examine whole diet, keep a food diary, & try to correlate your upset stomach with intake of any foods & other variables.

Sorbitol: Watermelon contains a sugar called sorbitol. People who have a sorbitol intolerance may develop gas, loose stools ; GI upset when they eat watermelon.