I have a vague sort of understanding that dietary fiber is material that doesn’t get digested, and thus somehow eases defecation. But I have little to no understanding of exactly what the differences between soluble and insoluble fiber are, which are good for what purposes, and so on. A quick Wikipedia gave me some small idea, but mostly left me pretty confused. Anyone care to share the straight dope?
Soluble fiber: dissolves in water. It keeps water in your stool in a gel, instead of it all leaving in the large intestine, which makes it easier to poop and reduces things like hemorrhoids and anal fissures (cracks).
Insoluble fiber: doesn’t dissolve in water. It scrapes the sides of your intestines as it moves through, which may keep them clean of old stool and overgrown bacteria colonies, which reduces things like colon cancer, diverticulitis and diverticulosis.
Both kinds of fiber provide “bulk” for the stool. Think about how hard you have to work to squeeze the last bit of toothpaste out of the tube - that’s how hard your intestines have to work to squeeze unfibered food through you. Add fiber, you add volume, and we all know how much easier it is to get toothpaste out when the tube is full, right? Plus, fiber makes you feel fuller, without adding any calories at all, which is good for weight loss or maintenance of a healthy weight.
Both are important for a healthy gut, and if you’re eating the standard American diet, you’re not getting enough of either. They’re not really differentiated on most food labels, so just try to get 25-30 grams of “fiber” per day (most USAians get about 5-8 grams a day!)
Best foods for fiber - both kinds? Unprocessed or minimally processed vegetables and grains. Try whole grain breads, pastas and rice. There are even a few “made with whole grain” breads which are essentially white bread with added fiber that are soft and fluffy but have up to 3 grams of fiber per slice. (I’m a white and fluffy bread fan, 'though I’ve mostly switched to the brown stuff.) Leave the skins on your veggies whenever possible, and don’t cook them to a mush. Add a salad to your lunch and dinner whenever possible.