How Older Adults Can Safely Boost Fiber

Insoluble fiber, on the other hand, doesn’t break down in your body. All that indigestible roughage helps keep you feeling full for longer and also keeps things moving through your system to prevent constipation. Berries, apples and pears with their skins, broccoli stems, green beans, whole grains and beans and legumes all have plenty.

The thing is, even though research exists into how each type of fiber helps with specific conditions, some studies don’t distinguish between the two. After all, whenever you eat something with fiber, you’re getting both — along with other, less-studied types, not to mention all the other nutrients that come with plant foods. Ultimately, what matters may be the way the different types of fiber work together, which scientists are still researching. 

Resistant starch: the unsung fiber

In basic terms, soluble fiber forms a gel-like substance in your digestive system, then feeds your gut bacteria. Insoluble fiber provides bulk that moves through you without breaking down. Resistant starch does a little of both, so it’s actually considered a fiber. Studies show it can help with blood sugar control.

Like fiber, starch is a complex carbohydrate. It consists of long chains of glucose molecules, which takes time for your body to separate and access for energy. With many starches, that happens in your small intestine.

But some starches are even slower to break down. Known as resistant starches, they go through your stomach and small intestine without being digested, just like insoluble fiber. Once resistant starch reaches your large intestine, however, it becomes prebiotic food for the friendly bacteria in your gut, which ferment it just like soluble fiber.

Starches change with heat. Certain foods, like raw potatoes, contain one kind of resistant starch. Cooking makes that starch gel-like and easily digestible, which contributes to potatoes’ bad rep. Cool down cooked spuds, though, and the starch transforms again, into a different kind of resistant starch. That holds true for other starchy foods, like rice, pasta, white bread and beans.

The cook-cool transformation into resistant starch only happens once, Slavin says. “If you throw the food into another recipe and use it, that doesn’t go away. It’s there forever.”

So if you can, try to cook starchy foods a day or more ahead of time, refrigerate them and reheat as needed. 

Refined fibers have benefits, but maybe not what you expect

Foods and supplements routinely tout added fiber on their labels, from the usual suspects like breakfast cereal to ice cream to soda. Sixteen types have been approved by the Food and Drug Administration. Many, but not all, are derived from plants.

To gain FDA approval, the makers of these fibers had to prove they provide a health benefit — except it may not be the benefit you’re looking for.

One of the most common added fibers is inulin, which is derived from chicory root. It helps with calcium absorption.