Consumers understand the importance of fiber, with the 2011 “International Food Information Council (IFIC) Food and Health” survey reporting that 62% of shoppers seek out fiber when buying packaged foods or beverages, and 56% try to consume “as much as possible”2.
Despite the solid science and awareness, current fiber intakes are alarmingly low, with less than 3% of adults and children meeting their daily fiber needs3, prompting the 2010 Dietary Guidelines for Americans to once again classify fiber as a “nutrient of concern.”
It appears difficult to obtain enough fiber from common foods. For example, only 40% of Americans consume fruit and vegetables more than two times per day4. Of concern, children aged 2 years and older have usual intakes below the recommended amounts of fruit (80%) and vegetables (89%)5.
Many foods simply are not considered a “good” source of fiber, defined as equivalent to 10-19% of the Daily Value (DV), or 2.5-4.9g per reference serving. Fewer foods are considered an “excellent” source of fiber, defined as equivalent to ≥20% of the DV or ≥5g per reference serving6. Thus, attempts by the food industry to fortify and enrich products with fiber can address a critical need for the population’s health.
Definition and Sources
Fiber includes carbohydrates and lignin that escape digestion in the upper gastrointestinal tract; undergo complete or partial fermentation in the colon; and exert varying beneficial effects, depending on type7. Soluble fiber attracts water during digestion and becomes viscous, trapping lipids and bile acids (the metabolite breakdown product of cholesterol). These include various gums, pectins,-glucans, oligosaccharides, resistant dextrans and resistant starches. Insoluble fiber is found in foods such as wheat bran, vegetables and whole grains.
Functional fibers are those that are added to foods or provided as supplements, and include (but are not limited to): “isolated, nondigestible plant (e.g., resistant starch, pectin and gums); animal (e.g., chitin and chitosan); or commercially produced (e.g., resistant starch, polydextrose, inulin and indigestible dextrins) carbohydrates”8. (See chart, “Types, Effects and Sources of Fiber Ingredients,” for an overview of the various fiber ingredients that are available to food manufactures.)
There is an abundance of epidemiologic and scientific data supporting the positive benefits of fiber in reducing the risk of a number of chronic conditions, including ischemic heart disease; stroke; atherosclerosis; type 2 diabetes; overweight and obesity; insulin resistance; hypertension; dyslipidemia; various cancers, including colon and breast; and gastrointestinal disorders, such as diverticulosis and irritable bowel disease9,10.
The most recent Academy of Nutrition and Dietetics (formerly the American Dietetic Association) position paper on dietary fiber and health provides evidence to suggest that fiber protects the cardiovascular system by interfering with cholesterol and bile acid absorption, thus lowering blood cholesterol and low-density lipoprotein (LDL) cholesterol. Another proposed mechanism is a delayed absorption of fat and carbohydrate, which leads to increased insulin sensitivity and decreased levels of circulating triglycerides11.
Well-controlled intervention studies have shown that for each additional gram of water-soluble fiber (in particular -glucan from oats and barley, psyllium, pectin and guar gum) in the diet, serum total and LDL cholesterol concentrations decrease by anywhere from 5-13% and 7-15%, respectively12. Information published on the consumption of cereal ﬁbers from bran and whole grains shows a reduced risk of arterial and peripheral disease of 25-35% for the highest whole-grain consumers in comparison to those eating lower amounts13,14.
Fiber’s potential role as a protective agent in blood pressure (BP) lowering is an interesting area of study. Jiang He, Ph.D., and coworkers have reported that 8g/d of soluble fiber from oat bran produced a moderate BP-lowering effect (systolic and diastolic) in a total of 55 participants aged 30-65 that had untreated, but higher-than-optimal, BP or stage-1 hypertension15. Notably, foods containing -glucans from oats also have been shown to significantly reduce both systolic and diastolic blood pressures in obese subjects16 and could control BP to the point where patients can reduce their dosages of hypertensive drugs17.
The role fiber might play in influencing the inflammatory serum compound C-reactive protein (CRP) also is of scientific interest. In cross-sectional and longitudinal analyses of 524 subjects, the likelihood of elevated CRP concentrations was 63% lower in participants in the highest quartile of total fiber intake than in participants in the lowest quartile, suggesting dietary fiber is protective against high CRP levels18.
Viscous dietary fibers also have been correlated with moderating both blood glucose and insulin19. Insoluble fiber, on the other hand, does not absorb water but is also beneficial, in that it increases insulin sensitivity20. The consumption of 10g/d of soluble fiber from -glucans resulted in beneficial effects on postprandial insulin levels21 in normoglycemic obese women at risk for insulin resistance. Fiber derived from vegetables also has been associated with decreased risk of diabetes in older people22.
Although data consistently show positive effects of fiber intake on biomarkers of diabetes in adults, this relationship has not been adequately assessed in children—although limited reports are positive, with psyllium supplementation decreasing postprandial serum glucose levels23.
The extent of emerging health benefits of various forms of fiber is impressive. In more than 1,000 cases, an inverse association was observed between intake of total fiber and the risk of colon cancer per an incremental increase of 10g/d24. And, a negative association was reported between total dietary fiber and fiber intake from fruits, vegetables and grains, and the risk of colon polyps among 2,818 men and women, with vegetable intake showing the greatest benefit25. It has been estimated that risk of colon adenoma—a leading cause of cancer death in the U.S.—can be reduced by 25-35% through dietary intervention, specifically via increased fiber intake. Both studies identify a protective role of dietary fiber intake in the prevention of colon cancer.
A statistically significant inverse association was found between total dietary fiber and fiber fractions intake and breast cancer risk in 438 women with primary breast cancer26. Vegetable and fruit fiber showed the highest inverse association with breast cancer risk.
Interesting new research suggests fiber might even enhance bone health. Soluble corn fiber and soluble dextrin fiber increased bone mineral (BM) content in rats after 12 weeks of feeding, resulting in increased total bone mineral density, cortical area and cortical thickness27. With an aging population prone to falls, such intriguing findings are indeed significant.
Role in Weight Control
Dietary fiber-containing foods often require longer chewing times before swallowing, thus influencing how much one may consume. Because of water-absorption capacity, soluble fibers create a gel-like chyme in the stomach, resulting in a sense of satiety without the addition of significant calories. This concept of “caloric displacement” promotes the use of low-calorie-density foods or supplemental fiber to achieve fullness without excessive energy consumption28.
Viscous fibers also have been shown to slow gastric emptying29 and produce a delayed pre-meal rise of ghrelin, a hormone which stimulates hunger. This delay is believed to be due to a slowing of the absorption of glucose and amino acids, and a resultant increase in the delivery of these nutrients to the small intestine30.
A significantly lower energy intake was found following the consumption by 22 men of 48g of resistant starch (RS) compared to a placebo supplement31. A significantly lower postprandial insulin response was noted following the RS supplement. This research compliments that of Anderson, et al, who reported consumption of a whole-grain corn flour with an RS content of 66% reduced cumulative food intake by 15%, compared to a high-glycemic control32. These studies suggest that consumption of RS may be useful in the management of metabolic syndrome and appetite.
It has been argued that recommendations for fiber intake in children have not been emphasized as they have for adults, yet the threat of obesity to this segment of the population is serious33. Dietary intake analysis in children has shown an association between low dietary fiber and higher body fatness34. Over a two-year period, increasing levels of soluble fiber in the diets of 7-11-year-olds led to a small reduction of visceral body fat, whereas decreasing fiber intake was associated with a 10% increase of visceral body fat35.
Fiber’s essential role in optimal health and its ability to reduce the risk of many diseases signals the importance of providing the population with fortified foods and beverages.
The 2011 “IFIC Food and Health” survey found that taste and price are the primary factors influencing purchasing decisions, with healthfulness and convenience also deemed important2. Challenges to increasing fiber intake are reported to include taste, texture, color and moisture content, in addition to the perception that the cost is greater36. Innovations in ingredient and product development, however, are providing solutions and proving to both consumers and marketers that fiber-containing foods do not, in fact, taste like “cardboard,” but can taste good and be “good for you.”
1. Food and Nutrition Board, Institute of Medicine of the National Academies. Dietary reference intakes for energy, carbohydrate, fibre, fat, fats, cholesterol, protein, and amino acids. 2005. Washington, DC: National Academies Press.
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