Gee, I don't know. Did you Google it... "Why does oatmeal clog my friend up

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All I have ever heard about oatmeal, is that it is really good for you. Does your friend drink enough water
Unless your friend has a hidden medical problem in the intestines, or wherever, tell your friend that when increasing the fiber content in his diet, it's best to take it slow. Add just a few grams at a time to allow the intestinal tract to adjust, otherwise, abdominal cramps, gas, bloating, and diarrhea or constipation may result. And...
Drink at least 2 liters (8 cups) of fluid daily.Maybe your friend doesn't drink enough liquids after eating oatmeal, you know, maybe your friend eats 3 bowls of it, and then he's out the door, not drinking any water with it. Then a couple hours later, whoa, .... it clogs him up.
Oatmeal is a rich source of soluble fiber.
Soluble fiber retains water and turns to gel during digestion, it also slows digestion and nutrient absorption from the stomach and intestine, as mentioned in the above post.
Tell your friend that fiber is very important to a healthy diet, and drinking enough water each day is a must. And if your friend still has problems eating oatmeal....maybe he needs to give it up
