Role of Fiber in Nutrition

Fiber is an indigestible carbohydrate made by plants.  Fiber provides structural support for plants the way bones do for the human body. Fiber can’t be digested and absorbed; thus, it is not classified as a nutrient. Nonetheless, accumulating evidence suggests that fiber plays important roles in nutrition and gastrointestinal health beyond its long-recognized role in helping to prevent constipation.

Types of Fiber

Currently, scientists recognize that there are two major types of dietary fiber, soluble and insoluble, and those types of fiber play different but equally important roles in the prevention of disease.

Soluble Fiber

Although it is impervious to digestive enzymes, soluble fiber partially dissolves, forming a gelatinous substance, when it comes in contact with the fluids in the intestinal tract. Soluble fiber slows the emptying of the stomach and small intestine. That is why many home remedies for diarrhea suggest eating fruits like apples, pears, and bananas that are rich in the soluble fiber pectin. Pharmaceutical manufacturers also add pectin to popular over-the-counter anti-diarrhea medications.

Within the past 15 years, researchers have recognized an important new role for soluble fiber-as a treatment for high cholesterol. It seems that the gelatinous substance formed when soluble fiber comes in contact with intestinal fluids acts like a mop or sponge that can soak up cholesterol in the gut and carry it out of the intestinal tract. This is why eating oatmeal for breakfast each morning can decrease cholesterol levels.

Insoluble Fiber

Sometimes called roughage, insoluble fiber (like cellulose) helps prevent or relieve constipation. Insoluble fiber absorbs water, which causes it to expand in size and increase the bulk and fluid content of the food residue in the intestines. The added bulk exerts pressure on the inside of the intestinal wall; the intestine responds with muscle contractions that speed up the passage of food residue through the GI tract. The water associated with the fiber also softens the feces, making it easier for them to be eliminated.

Based on population studies, some researchers believe that diets high in fiber help prevent colon cancer, but the mechanism for this action is not well understood.

Clinical studies have shown that eating a combination of soluble and insoluble fiber can help prevent and treat obesity and diabetes. Because both types of fiber add volume to the diet, these forms of fiber can help people who are watching their weight feel satisfyingly full without increasing their calorie intake. Both types of fiber also slow the release and absorption of glucose from the intestine during digestion. This action helps keep blood glucose (blood sugar) levels stable for a longer period of time. Maintaining a stable blood sugar level can help people improve their weight control efforts because their brains aren’t signaling them to find food to boost glucose levels. Keeping blood sugar at a moderate level can also reduce the need for people with diabetes to inject themselves with extra insulin. This is a beneficial result because insulin injections often cause a variety of side effects.

How Much Fiber Should I Eat Each Day?

Interpreting fiber research studies is complicated by the fact that diets high in fiber also tend to provide other nutritional benefits like low fat and sugar content and a relatively higher amount of phytochemicals and vitamins. Still, it appears that eating 20-35 grams of fiber each day can provide valuable health and weight management benefits. The recommend range of fiber intake is quite broad because people’s sensitivity to fiber and other natural laxatives found in plant-based foods varies. Finding the right level of dietary fiber is a matter of trial and error. It is best to increase fiber intake gradually, (3-5 grams a day) to give your gut time to adjust to the new food composition.

To help meet your fiber goal remember to make half your grains whole grains.

A good way to meet your fiber intake goal is to eat the recommended amounts of fruits and vegetables and at least three servings of whole grain foods each day. The interactive and customizable food guide pyramid that can be found at www.mypyramid.gov can estimate your fiber needs and recommend foods that can help you meet your fiber goal.