Fiber is an interesting nutrient. On the one hand, our bodies are completely incapable of digesting it—the fiber we do ‘digest’ is actually digested by our gut bacteria. On the other hand, fiber is associated with a huge list of positive benefits, from lowered blood lipids to reduced belly fat to decreased incidence of colon cancer. How can a nutrient we can’t even digest provide so many, and so varied of, benefits?
To better understand the crucial role fiber plays not only in weight maintenance and weight loss, but in health in general, the first step is to understand what exactly fiber is.
Fiber Is Varied
When nutritionists talk about fiber, the first thing to know is that there are two primary types:
- Soluble Fiber, which can dissolve in water
- Insoluble Fiber, which cannot dissolve in water
These might seem like unimportant differences, but they actually make a huge difference in the way fiber behaves in our body.
Soluble fibers tend to gel, dramatically increasing their viscosity, or thickness. When we consume soluble fiber, it gels in the stomach, making the chyme (the liquidy digested food that passes from the stomach to the small intestine) thicken. If you imagine how much slower molasses drains from a bottle compared to water, then you get the picture of how soluble fiber slows down the rate of your stomach emptying!
Insoluble fibers, on the other hand, absorb less water, do not gel, and do not significantly affect how fast food empties from your stomach. In contrast to soluble fiber, insoluble fiber makes food travel faster through your intestines by adding bulk to it—in this way, insoluble fiber is great in helping to prevent constipation. Since insoluble fiber gains so much bulk, it too can make you feel fuller.