Sure, grains get most of the glory for fiber’s health benefits, but let’s not forget the fiber power of fruits. A broad body of research has linked dietary fiber from a variety of plant foods, including fruits, vegetables, grains, legumes, nuts and seeds, with a number of health bonuses. These include preventing constipation, lowering the risk of digestive conditions, lowering blood cholesterol levels, helping to control blood sugar levels, aiding in weight loss, and lowering the risk of colorectal cancer.
Fiber is a group of carbohydrates that resist digestion in the small intestine, because humans lack the enzymes to digest them. Classes include lignin, cellulose, beta-glucans, hemicelluloses, pectins, gums, inulin and oligofructose, and resistant starch. Added to that list are functional fibers—isolated fibers that have human health benefits—including psyllium, chitin and chitosan, fructooligosaccharides, polydextrose and polyols, and resistant dextrins. As established by the Institute of Medicine, Washington, D.C., the AI (Adequate Intake) for total fiber for men ages 18 to 50 is 38 grams per day, and for women ages 18 to 50 is 25 grams per day, yet Americans only average 14 to 15 grams of total fiber intake per day.
Healthy focus on fruitful fibers
With so much good news circulating on fiber’s health benefits, more attention is falling upon fruit as a source to help ratchet up fiber intake. Many fruits are exceptional sources of fiber. For example, 1 cup of pitted uncooked prunes (174 grams) contains 12.1 grams of fiber, an Asian pear (275 grams) contains 9.9 grams of fiber, and 1 cup (123 grams) of fresh raspberries contains 8 grams of fiber. Fruits contain varying amounts of the dietary fibers lignin, cellulose, hemicellulose, pectin and gums.
While much research has investigated the effects of consuming a fiber-rich diet, little has been done to help us understand the unique health properties of specific fruit fibers. We know that consuming more fruit is a healthy habit linked with lower rates of chronic diseases. Whole fruits call upon a synergy of important nutrients, including vitamins, minerals, phytochemicals and dietary fibers, to produce these health attributes.
Fruits harness a number of fiber bonuses. They contain viscous fibers like pectin that slow the emptying of the stomach and might lower serum cholesterol. Fruits may also contain nonviscous fibers like lignin, cellulose and some hemicelluloses, which increase stool bulk, reduce transit time, and may help treat constipation. Reduced transit time promotes regularity and minimizes colon-cancer risk by decreasing the time that coloncytes are exposed to potentially carcinogenic wastes. Fruits are also rich in readily fermentable fibers, such as pectin, that increase beneficial-bacteria density and promote growth and healthy functions of the intestine. Fruit fibers have also been linked to lowered heart-disease-death risk. In a pooled analysis of 10 prospective cohort studies of dietary fiber intake in the United States and Europe published in the Archives of Internal Medicine (Feb. 2004; 164:370-376), researchers found the inverse association between fiber intake and coronary-heart-disease death was particularly high for cereal fiber and fruit fiber.
From fruit waste to fruit fiber
Fruit processors are taking a second look at fruit waste as a source of desirable functional fiber. It is estimated that 25% to 40% of the total fruits processed around the world turn up as fruit waste. The annual Florida citrus juice industry alone produces approximately 3.5 to 5 tons of citrus waste each year. Historically, fruit waste has been turned into compost or animal feed. But processors now appreciate that fruit waste, rich in dietary fibers and other bioactive compounds, are a hidden treasure. The use of apple pomace for the extraction of such products as fiber has increased. Tree Top, Inc., Selah, WA, dries peels and cores from their apple processing plants and mills them into apple fiber (3:1 insoluble fiber to soluble fiber). The USDA Agricultural Research Service is exploring the possibilities of recapturing coproducts, such as pectin, from Florida’s vast flow of citrus waste. A main source of juice in tropical regions, yellow passion fruit yields waste being investigated for its fiber attributes. The challenges for rescuing dietary fibers from fruit waste have included financial feasibility, stability and safety. Meanwhile, smart food producers are taking advantage of fruit fibers in product development. FruitSmart, Prosser, WA, developed a line of fruit products and ingredients, including fruit fibers made from fruit skins and pulp.
With fiber on everyone’s radar, fruit may certainly be the next fiber frontier.
Sharon Palmer is a registered dietitian with 16 years of experience in health-care and foodservice management. She writes on food and nutrition for newspapers, magazines, websites and books. Palmer makes her home in Southern California and can be reached at
info@sharonpalmer.com.