December 2013 Issue
A Soluble Fiber Primer — Plus the Top Five Foods That Can Lower LDL Cholesterol
By Judith C. Thalheimer, RD, LDN
Vol. 15 No. 12 P. 16
As many dietitians know, heart disease is the No. 1 killer of both men and women in the United States, accounting for one in every four deaths. Coronary heart disease (CHD) is the most common type, leading to angina, arrhythmias, heart attack, and heart failure, and it’s responsible for killing more than 385,000 Americans each year, according to the Centers for Disease Control and Prevention.
High blood levels of total cholesterol and low-density lipoproteins (LDL) are key indicators of CHD risk. The good news is that these risk factors can be influenced by dietary intake of foods that contain soluble fiber.
“Consuming legumes, oats, barley, nuts, certain fruits and vegetables, and psyllium as well as pectin found in fruits and berries can help lower LDL cholesterol,” says Sharon Palmer, RD, author of The Plant-Powered Diet and Plant-Powered for Life. “These foods contain soluble fiber, which research links to lowering total and LDL cholesterol levels and to reducing risk of heart disease, among other benefits.”
Consuming 5 to 10 g of soluble fiber per day reduces LDL cholesterol levels by approximately 5%.1 The National Cholesterol Education Program Expert Panel recommends consuming 10 to 25 g of soluble fiber per day and following a diet low in saturated fat and cholesterol to help lower blood cholesterol.
Fiber’s Many Faces
While many in the health care community use the term “soluble fiber,” the Institute of Medicine (IOM) recommends they stop because recent studies have suggested that other properties of fiber, such as physical and chemical structure, fermentation capacity, and viscosity, determine the effect on health outcomes. The IOM categorizes fiber as either dietary fiber or functional fiber.
Dietary fiber, which most often is a nondigestible carbohydrate, is the part of a plant not broken down by human digestive enzymes. The term soluble fiber originally was assigned to fibers that disperse in water, but it’s come to mean those fibers that form viscous gels and are fermented by colonic bacteria. Since not all fibers with those traits truly are soluble, fiber often is classified instead as viscous (forming a gel in water) vs. nonviscous or fermentable vs. nonfermentable.
Functional fiber is fiber that has been extracted from plant or animal sources, manufactured, or synthesized and then added to processed foods. This includes natural mucilages such as psyllium; chitin from the exoskeletons of crustaceans; synthetic fructooligosacchrides, polydextrose, and polyols; and resistant dextrins.
While there are several accepted ways to classify fibers, the most popular grouping is based on how they react in water. “Soluble fiber dissolves in water, forming a gel,” Palmer explains. Insoluble fiber (mainly cellulose, hemicellulose, and lignin) does not. Though there are several kinds of soluble fiber (see Table 1 below), no major differences have been found in their abilities to lower cholesterol.2
Information is still emerging on the exact mechanisms by which soluble fiber helps lower cholesterol, but “it’s believed that viscous fiber interferes with the reabsorption of bile acids in the intestines,” explains Joan Salge Blake, MS, RD, LDN, a spokesperson for the Academy of Nutrition and Dietetics. “Bile acids are high in cholesterol and are released into your intestine by your gallbladder to help with the digestion of fat. The bile acids are likely ‘grabbed’ by the fiber before they can be reabsorbed by the body. They then end up being excreted along with the fiber in your waste products. Your body replaces these lost bile acids by removing cholesterol from the blood to generate new bile acids in the liver. Blood cholesterol levels are lowered as a result.”
Soluble fiber may help lower LDL cholesterol by playing a role in the production of short-chain fatty acids (SCFAs). Soluble fibers are prebiotic, which means they serve as food for the beneficial bacteria in the human gut. “This type of fiber is fermented by bacteria in the colon,” Palmer notes. This produces gases and SCFAs. While the gases occasionally may cause discomfort or embarrassment, SCFAs have been linked to reduced blood cholesterol levels.3
5 Foods That Top the Charts
The best dietary sources of soluble fiber that dietitians can tell clients about include the following4:
1. Beans: Beans are soluble fiber superstars. One cup of black beans has 4.8 g of soluble fiber, while Navy beans have 4.4 g and light-red kidney beans have 4 g. All beans are good choices, though.
2. Oat cereals: Oats are high in soluble fiber, making oat cereals a better choice than bran for this particular dietary component. A bowl of oatmeal made from 3/4 cup of dry oats contains 3 g of soluble fiber. A serving of cooked oat bran cereal (3/4 cup) has 2.2 g, and 1 cup of oat flakes has around 1.5 g.
3. Brussels sprouts: Vegetables are good sources of soluble fiber, with Brussels sprouts topping the list with 2 g per 1/2 cup. The flesh of sweet potatoes is next with 1.8 g followed by asparagus with 1.7 g. Brussels sprouts tossed with a little olive oil, salt, and pepper and roasted for 30 to 45 minutes in a 400-degree oven have a sweet, rich flavor that can win over skeptics.
4. Oranges: Fruits are a tasty way to get soluble fiber, and oranges are the top pick, with 1.8 g of soluble fiber in one small orange. Eating four apricots with the skin provides 1.8 g as well. At this time of year, apples and pears are other grab-and-go fiber-rich favorites.’
5. Flaxseeds: While 1 T of peanut butter has 0.3 g of soluble fiber, flaxseeds have an impressive 1.1 g per tablespoon. Patients and clients can sprinkle ground flaxseeds on hot or cold cereal, for example.
Easy to Incorporate
“An easy way to boost soluble fiber intake is to frequently eat oats for breakfast and to include legumes in your diet at least a few times a week,” Palmer suggests.
“Your patients and clients don’t need to count grams of fiber if they lead with fruits and veggies,” says Susan E. Adams, MS, RD, LDN, an assistant professor in the nutrition program at LaSalle University of Philadelphia. “If they follow MyPlate and fill half of their plate with fruits and vegetables at every meal, they will be well on their way to getting enough. It really adds up!”
— Judith C. Thalheimer, RD, LDN, is a freelance nutrition writer and community educator living outside Philadelphia.
Table 1: Types of Soluble Fiber
Grains (oats, rye, barley)
Pectin (sugar acids)
Fruits, vegetables, legumes, sugar beets
Seeds (guar and locust bean), trees (gum acacia), seaweed (carrageenan), microbes (xanthan gum)
Chicory, onions, wheat, Jerusalem artichokes; increasingly added to processed foods
— Source: Tungland BC, Meyer D. Nondigestible oligo- and polysaccharides (dietary fiber): their physiology and role in human health and food. Comp Rev Food Sci Food Safety. 2002;3:90-109.
Quick and Easy Pantry Bean Salad
This quick and easy three-bean salad can be made in minutes from pantry ingredients. As a main course or side dish, a 1-cup serving has approximately 4 g of soluble fiber. This versatile base changes flavor depending on the dressing used and can be mixed with cold pasta and/or any leftover diced vegetables, meats, or poultry for endless variety. (If adding ingredients, add more dressing to taste.)
One 15-oz can dark-red kidney beans, rinsed and drained
One 15-oz can low-sodium black beans, rinsed and drained
One 16-oz can chickpeas, rinsed and drained
1/2 cup (or one 2 1/4-oz can, drained) pitted and sliced black olives
1/2 cup diced red onion (optional)
1/4 cup reduced-fat Italian-style salad dressing
Stir all ingredients together in a large bowl. Eat right away or cover and refrigerate 1 hour or more to let flavors blend.
Nutrient Analysis per serving
Calories: 291; Total fat: 5 g; Sat fat: 0 g; Trans fat: 0 g; Cholesterol: 0 mg; Sodium: 567 mg; Total carbohydrate: 47 g; Dietary fiber: 15 g; Sugars: 5 g; Protein: 16 g
— Recipe courtesy of JTRD Nutrition Education Services
1. National Heart, Lung, and Blood Institute. Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III): Final Report. NIH Publication No. 02-5215. Bethesda, MD: National Institutes of Health; 2002.
2. Theuwissen E, Mensink RP. Water-soluble dietary fibers and cardiovascular disease. Physiol Behav. 2008;94(2):285-292.
3. Hara H, Haga S, Aoyama Y, Kiriyama S. Short-chain fatty acids suppress cholesterol synthesis in rat liver and intestine. J Nutr. 1999;129(5):942-948.
4. Fiber content of foods in common portions. Harvard University Health Services website. http://huhs.harvard.edu/assets/File/OurServices/Service_Nutrition_Fiber.pdf. May 2004.