A balanced diet contains all the essential nutrients with a reasonable ratio of all the major food groups. The quantity of foods required to achieve a balanced diet may vary with age, gender, physiological status and physical activity. Our human system essentially requires macronutrients like carbohydrates, proteins and fats to avail and support the balanced diet. These macronutrients primarily support, promote and maintain overall well-being and good health. However, in addition to the macronutrients, a balanced diet may also include dietary fiber, antioxidants and phytochemicals.
Fiber is classified under the category of carbohydrate which is considered to be an essential nutrient. Fiber is naturally present in plants and its functional derivatives are Cellulose, Resistant Dextrins, Hemicellulose, Oligosaccharides, Resistant Starch, Chitins, Pectins, Beta-Glucans and Lignin.
Generally, most of the carbohydrates are broken down into sugar molecules by various enzymatic hydrolysis in human system. However, dietary fibers are not completely broken down into sugar molecules in the small intestine as humans lack the necessary enzymes to break down the chemical bonds present in these fiber molecules. Undigested dietary fiber then passes through to the large intestine, where some of them are fermented by bacteria present in the gut. The by-products of this fermentation process are carbon dioxide, methane, hydrogen and short-chain fatty acids (SCFAs). Certain types of fiber may cause an increase in gas production which leads to bloating.
Fiber is classified as soluble fiber and insoluble fiber.
• Soluble fiber:
It is fiber which readily dissolves in liquids. Some types of soluble fiber are viscous and hydrophilic, and will form a gel-like substance in the gastrointestinal tract during the digestion process. The other non-viscous type of soluble fibers are fermented in the large intestine to provide several physiological benefits. Soluble fiber may increase the fecal stool bulk as well as soften it so that it slides easily through the large intestine, helping with constipation. Soluble fiber is present in apples, oranges, grapes, dry beans, lentils, peas, barley, oats and the likes thereof.
• Insoluble fiber:
It is the type of fiber which does not readily dissolve in liquids and remains relatively unchanged in the gastrointestinal tract during the digestion process. Insoluble fiber prevents constipation by adding bulk to fecal content in the large intestine. Generally, insoluble fiber is minimally fermented. Insoluble fiber is present in vegetables, whole grain products, whole wheat bread, bran, pasta, crackers, edible seeds, brown rice and the likes thereof.
The US Dietary Guidelines recommends a daily requirement of dietary fiber of 21g to 38g, depending on calorie requirements. Currently, dietary fiber intake among adults in the United States averages about 15g a day, which is only about half the recommended amount.
The dietary fibers of selected foods are provided below. The portion, intake, size of the food to be consumed is based on the individual characteristics and based on country-specific guidelines.
Fiber is complex carbohydrate which is not digested in the small intestine and generally comes from plant sources. It is found in a wide variety of foods. Based on the mechanisms, the three predominant forms of fiber includes bulking, viscosity, and fermentation.
Fibers decrease the risk of constipation and gastrointestinal tract infection, specifically the disease or disorder associated with the colon. In the intestines or colon, fibers absorb water, which leads to the formation of bulk and promotes the regularity of normal intestinal functions. There is a wide variety of plant sources, cereals and legumes available to act as bulking agents. Specifically, wheat bran, cellulose and psyllium act as bulking fiber.
Viscous fibers decrease the absorption of lipoproteins, other forms of cholesterol and nutrients by thickening the contents of gastrointestinal tract. These actions may slow down the movement of essential and non-essential nutrients into the gastrointestinal tract walls. Other advantages also include: reducing or lowering the cholesterol levels in the blood and decreasing the glycemic response or blood sugar levels. The viscosity of the fiber is directly proportional to the effectiveness in reducing absorption. There is also a wide variety of plant sources available which act as bulking agents. Specifically, beta-glucan, guar gum and psyllium acts as viscous fiber.
It is reported that trillions of bacteria live in the healthy human gastrointestinal tract, which in turn play a vital role in human health and well-being. Dietary fibers play a vital role in feeding the gut microbiota and microflora, which is crucial for the health of the gut. The bacteria present in the colon interact with fibers through a process of fermentation and produce the short chain fatty acids (SCFAs). These SCFAs have multiple beneficial effects in maintaining the health and integrity of the colon and the gut system. It increases the bowel regularity by peristalsis movement. The SCFAs also trigger various biochemical pathways which are assumed to provide a wide range of health benefits. They also play a vital role in the absorption of essential minerals such as calcium and magnesium.
Nature provides the support for humans to obtain dietary fibers in the form of fruits, vegetables, whole grains, and legumes which supports for normal well-being. Dietary fibers are indicated for supporting the gut/digestive system. Consuming fibers also have enormous benefits for other body systems. For one, consumption of fibers also help develop the immunity in the gut, produces beneficial probiotics and aids in reducing excess amount of cholesterol and other toxins from the human system. Evidence also points to increasing fiber intake being associated with decreasing risks of common disorders such as cardiovascular disease, cancer, diabetes / control of blood sugar, skin health and weight management/obesity.
Below are few reported and emerging evidence which supports potential benefits of dietary fibers in humans: