Joan Endyke: Type of fiber matters

Joan Endyke

Q: I’m now understanding the value of whole wheat products versus enriched. And I’m understanding fiber. But why oatmeal?

Could a person just eat a whole wheat sandwich each morning to gain benefits for the heart? It’s like the oats go right to the heart and on the way just flush out any clogged arteries. How does it really work?

How can oatmeal have such a rapid benefit to the heart (blood pressure, etc.).

Linda Adams, Richmond, Va.

A: The value of oatmeal has to do with the type of fiber it contains, soluble fiber. Oatmeal helps prevent the absorption of cholesterol from the digestive tract into the blood stream. Less circulating cholesterol translates into lowered risk of clogged arteries.

Plant foods contain two types of fiber: soluble and insoluble.

Humans cannot digest either because we lack the necessary enzymes.

The loosely knit chemical structure of soluble fiber allows it to bond with water molecules. When it absorbs water, (the reason why it is called “soluble”) it also binds with bile acids (needed for cholesterol transport to the blood stream), cholesterol, and other substances.

This spider-web like structure moves through the digestive tract until it is eliminated.

Soluble fiber also plays a protective role in diabetes. Its spongy, gel-like structure forms a barrier in the digestive system, blocking enzymes from digesting starches and sugars.

This allows them to be digested slowly and prevents large, rapid surges of sugar in the blood stream reducing insulin needs.

Soluble fiber is found in many foods, not just oatmeal. Rich sources include legumes, like navy, pinto, and lima beans, apples, citrus fruits, flax seed, barley, carrots, and psyllium.

Whole grain oatmeal contains the bran (outer layer), the germ and endosperm of the plant with most of the fiber found in the bran.

Products that contain unrefined oat bran, like some cold cereals, and muffins are another option for breakfast. But be aware some oat bran muffins contain too much saturated or trans fat, detrimental for the heart.

Oatmeal and other types of soluble fiber will provide little protection for your heart if the rest of your diet is high in cholesterol, saturated, and trans fat – found in bakery items, fast foods, red meats, cheese, butter and other full-fat dairy items.

The best protection comes from limiting these foods and enjoying low-fat foods along with soluble fiber-rich foods.

Wheat bread, containing whole wheat flour and wheat bran, along with nuts, and many vegetables are good sources of insoluble fiber.

This type of fiber does not directly affect cholesterol but protects in other ways. It adds bulk in the intestine, creating a feeling of fullness for a long time, which can reduce calorie intake and promote weight loss. A healthy weight greatly protects the heart.

Insoluble fiber helps move things along the digestive tract – reducing the incidence of constipation, hemorrhoids, irritable bowel syndrome and diverticulosis. Both types of fiber are beneficial.

Joan Endyke is a registered dietitian with a master's degree in nutrition and food science, and also a certified personal trainer. She is the nutrition director at Fitness Unlimited in Milton, Mass. Readers may send questions about nutrition to Endyke at Fitness Unlimited, 364 Granite Ave., Milton, MA 02186 or by e-mail to

The information in this column is not intended to diagnose individual conditions. Readers should see their doctors about specific problems.