Actually bananas can both cause constipation and help cure it. They can be used in milkshakes as thickeners, and the same can be said for you bowels. It just depends on the pre-existing problems, or lack of.

Also I don't know why they say not to refrigerate banana's. Sure the skin will turn black, but the flesh of the banana, which is the bit we eat, stays firm and fresh tasting.

Also if you want to ripen some fruit. Put them in a plastic bag with a ripe banana. Apparently they increase the rate which other fruit ripen.