Since FODMAPs are harder for some people to digest and absorb, they can be fermented by bacteria in the intestine and cause symptoms. There are two main reasons FODMAPs cause symptoms:
If you have extra water in your intestines, your belly may feel bloated and even look swollen. More gas in the intestines can also cause you to feel bloated or your belly to look swollen.
Extra water and extra gas in your intestines can lead to cramping or abdominal pain. Bloating from extra water and gas can also be painful.
FODMAPs trigger your digestive system to draw in extra water. If you are sensitive to FODMAPs, your bowels may contract more than normal to move the fluid through. The extra contractions cause the stool to move through your body faster. This causes diarrhea.
When bacteria in the intestine break down sugar, they produce gas. If your intestine is being fed more FODMAPs than usual, the bacteria there will produce more gas.