Why does oatmeal constipate me even though i drink a ton of water?

Possibly the process: Instant oats are not as good as old fashioned rolled oats. There is no insoluble fiber in the over-processed instant oats per the nutrition data from quaker. It has only one gram of soluble fiber. While old fashioned oats have 2 grams of soluble fiber and 2 grams of insoluble fiber, or roughage. This may explain it if you eat instant oats.