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THE F WORD

Written by: Abigail Moore, Dietetic Intern
Friday May 31, 2019

Fiber is in many of the foods that make up your diet, however, more often than not, the breadth of benefits that fiber can provide are often not well known by the general population.

What is It?
Fiber can be defined by dividing the term into two distinct categories. Dietary fiber refers to nondigestible (not absorbed within the small intestine) carbohydrates (cellulose, hemicelluose, β-glucans, pectins, gums fructans and resistant starch) and lignin which are all found intact within plants. Dietary fibers may or may not be fermented within the large intestine. Dietary fiber can also provide fuel to cells within the colon. Functional fiber, on the other hand, is made up of isolated nondigestible carbohydrates which have positive physiological effects within the human body.

Intakes:
Foods with high amounts of dietary fiber generally provide vitamins, minerals, water, and various phytonutrients. Within the US, grains and vegetables are the primary sources of fiber, with the biggest contributors coming from white flour (16% of US dietary fiber) and white potatoes (9%). Although these foods are not exceptionally high in fiber, they are consumed in large amounts throughout the country. Whereas, foods like legumes, only make up 6% of the US fiber intake even though they are high in fiber, because of low consumption. Fruits also contribute only 10% of overall fiber. Individuals in the United States generally consume approximately 15g of fiber per day.

Recommendations:
Dietary Reference intakes recommend consumption of 25 g of fiber for adult women and 38 g for adult men. When asked about their perceptions of dietary intake, 73% of individuals though that their fiber intake was “about right” even though the individuals surveyed demonstrated a mean intake below 20g/d.

Disease Incidence/Risk Reduction:
It is well known that populations that consume more dietary fiber have less incidence of chronic disease. Research has suggested that high fiber intake decreases prevalence of GERD, gastric cancer, esophageal cancer, breast cancer, peptic ulcer disease, constipation, hemorrhoids, gallbladder disease, diverticular disease, coronary heart disease, stroke, hypertension, diabetes, obesity, and a variety of other chronic conditions. Higher intakes of dietary fiber can also help to improve blood lipid profiles, blood pressure, and C-reactive protein levels. Dietary fiber can even improve the strength of the immune system via providing prebiotics to promote positive impacts on the gut microbiome and strengthening of the gut barrier, and the production of short chain fatty acids.

Obesity prevalence is decreased in populations with high fiber intake and it is estimated that high‐level fiber consumption reduces risk for gaining weight or developing obesity by approximately 30%.

Fiber can decrease risk of diabetes and promote blood glucose control for those who have diabetes. A 17-study meta-analysis suggests that a 2g/d increase in cereal fiber intake can reduce the risk of developing type 2 diabetes by 6%, while increasing intake by 10g/day can decrease risk by 25%. Diets providing 30-50g/day have been shown to consistently promote lower blood glucose levels largely due to slowed gastric emptying.

Approximately 60% of heart disease development is thought to be attributed to dietary patterns. Studies have demonstrated a 29% lower prevalence of heart disease in individuals with high intakes of dietary fiber. Furthermore, studies have shown that high intakes of whole grains have led to a 26% decrease in ischemic stroke incidence.

Dietary fiber can also help with chronic gastrointestinal conditions such as constipation, by promoting regularity and increased stool weight. Analysis of populations in 12 different countries demonstrated that higher stool weight had a positive association with decreased prevalence of colon cancer. Dietary fiber can also help to prevent the formation of diverticula and help with management of inflammatory bowel disease symptoms.

Specific fibers (inulin, oligosaccharides, resistant starch, etc.) have also been shown to improve mineral absorption. This is especially significant for calcium and magnesium.

Weight Control:
A high fiber diet will promote healthy weight maintenance and keep you feeling fuller longer. Fiber promotes this satiation by slowing gastric emptying. Additional causes of satiation result from an increase in the amount of chewing required when consuming high fiber foods and the binding of water by specific types of fiber, both which lead to gastric distention. Furthermore, fiber displaces other sources of energy from the diet, and decreases the efficiency of absorption within the small intestine. Research has demonstrated a 10% average decrease in energy intake when an additional 14g of fiber was added to the diet. Fiber satiation was seen to have the greatest impact when consumed intrinsically within whole foods. For example, one study demonstrated that 200g of whole carrots led to higher satiety and led to a greater decrease in energy intake for the rest of the day when compared to pureed carrots, or carrot nutrients.

Future of Fiber:
Health care professionals should encourage intake of high fiber foods, including legumes, whole grains, vegetables, and fruits. Consumers should look to increase their intake of these foods and incorporate new sources of dietary fiber into their typical diet plan. It is helpful to use tools such as the MyPlate and the dietary guidelines when attempting to analyze sufficiency of fiber content within the diet and/or increase intake. Consumers would likely benefit from finding ways to incorporate fiber into foods that they commonly consume already. This could include swapping foods, such as exchanging white bread for wheat bread, or adding in fiber sources to typical meals, such as adding fruits and/or nuts to yogurt. Other simple tips for increasing fiber intake include choosing whole fruits/vegetables over juices, snacking on fruits, veggies or nuts, reading labels to choose high fiber foods, and including at least two high fiber foods at each meal. The benefits of fiber have been demonstrated frequently throughout current available research, so increasing the fiber intake of the US population will help to strengthen our overall public health in significant ways. Eat more fiber and your body will thank you!

References:

Lattimer, J. M., & Haub, M. D. (2010). Effects of Dietary Fiber and Its Components on Metabolic Health. Nutrients, 2(12), 1266-1289. doi:10.3390/nu2121266

Slavin, J. (2013). Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients, 5(4), 1417-1435. doi:10.3390/nu5041417

Anderson, J. W. (2009). Health benefits of dietary fiber. Nutrition Reviews, 67(4). Retrieved March 3, 2019.

Gastrointestinal Transit Time, Glucose Homeostasis and Metabolic Health: Modulation by Dietary Fibers.
(2018). Nutrients, 10(3), 275. doi:10.3390/nu10030275

Gorman, M. A., & Bowman, C. (1993). Position of The American Dietetic Association: Health implications of dietary fiber. Journal of the American Dietetic Association, 93(12), 1446-1447. doi:10.1016/0002-8223(93)92252-s