From the National Library of Medicine, National Institutes of Health:
http://www.nlm.nih.gov/medlineplus/ency/article/002136.htm"Soluble fiber
attracts water and turns to gel during digestion. This slows digestion.
Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fiber supplement. Some types of soluble fiber may help lower cholesterol, but the effect on heart disease is not known.
Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It adds bulk to the stool and appears to help food pass more quickly through the stomach and intestines."
I think the part about attracting water is important. A soft stool is a wet stool. So get lots of soluble fibre and drink lots of water to ensure the stool does get wet.
The insoluble fibre might seem like a bad guy (adding bulk -
), but helping food to pass more quickly through the intestine, that's good. The faster the food moves, the less water extracted by the colon.
As always, it's a balance of soluble and insoluble that's important.
As for me, I eat oatmeal/porridge every morning because I think that slippery (almost slimy) texture is great for soft BMs. And mine are very soft. I add fruit like a cut up peach or pear, or dried cranberries. Anything to make it more interesting.