Q: I’ve heard that I should eat both soluble and insoluble fiber. What’s the difference?

A: In simple terms, soluble fiber dissolves in water and the insoluble kind doesn’t. Because it doesn’t break down, the insoluble fiber in whole grains, bran, nuts and vegetables passes through your digestive tract pretty much intact. This keeps your plumbing running smoothly by increasing fecal bulk and decreasing its transit time. But the soluble fiber found in oats, peas, beans, fruit skins and flaxseed forms a gel in the intestine, reducing cholesterol levels by limiting its absorption and slowing the release of glucose from food into the bloodstream. This helps impede fat storage.

So, yes, if you want to be lean and healthy, eat both types of fiber. Just avoid high-fiber foods, especially those high in insoluble fiber, right after workouts. This is the one time of day when you don’t want to slow the release of glucose into the bloodstream or inhibit an insulin spike.


Matthew Kadey is a registered dietitian and freelance writer who owns Fuel For Life.