Dietary fiber is classified based on its solubility. Soluble fiber can dissolve in water whereas insoluble fiber can't.
Soluble Fiber
Soluble fiber can dissolve in water, which slows down digestion. This is the type of fiber that is thought to lower blood cholesterol levels, which in turn reduces heart disease risk. It also helps regulate blood sugar levels.
In your diet, you get soluble fiber from:
- Oat bran
- Barley
- Psyllium
- Nuts
- Seeds
- Beans
- Lentils & peas
- Some fruits & vegetables
Insoluble Fiber
Insoluble fiber doesn't slow down digestion like soluble fiber does, rather it is linked to "laxation". Insoluble fiber adds bulk to your stools and actually makes food pass through your digestive system more quickly than it would without the fiber. This is the type of fiber that helps promote good bowel regularity and reduces constipation.
Insoluble fiber in the diet comes from:
- Wheat bran
- Certain fruits & vegetables
- Whole grains
Recommendations
Dietitians recommend that you don't fret about eating soluble vs. insoluble fibers. Instead, your focus should be on increasing and achieving recommended levels of total dietary fiber. Most high fiber foods will naturally have a combination of both soluble and insoluble fibers. For example, in fruit, the soluble fiber is found in the flesh and the insoluble comes from the peels. Eating the whole piece of fruit maximizes your fiber intake, and health benefits from fiber come from a combination of both types.
Here's an example of a high fiber food rocking equal amounts of soluble and insoluble fiber. This label is from Quaker Oats. You can see that per serving, you get 4 grams of fiber: 2 soluble and 2 insoluble.
