Dietary fiber comes from the carbohydrate parts of plants that humans cannot normally digest. By forming a viscous gel-like substance in the digestive system, fiber can slow the transit time of nutrients through the intestines and shield these nutrients from digestion. Evidence suggests that fiber can inhibit the absorption of sugar, cholesterol and various minerals. It may also affect the absorption of protein.
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Types of Fiber
Whole grains, beans, fruits and vegetables are all excellent sources of dietary fiber. Different types of plants can vary in the amount and kind of fiber that they contain. There are two types of fiber: soluble and insoluble. The soluble fiber is generally the one that impacts the absorption of nutrients. It's present in such plant components as pectin and gum. Each one may have a different effect, so it is difficult to make a single claim about fiber.
The effects of dietary fiber are absolutely essential to the utilization of protein in the human body. Proteins that are otherwise high in quality might in practice be relatively poor due to a low absorption rate. Because protein is essential to just about every physiological process in living organisms, significant changes in the absorption rate can have ramifications throughout the rest of the body.
Effects of Fiber
Numerous studies have explored the effects of fiber on protein digestion by measuring the degree of nitrogen loss in human excretion. Nitrogen is an important component of protein chemistry. Using this method, researchers can discover the amount of protein that the human body actually absorbs. As expected, the absorption rate could vary significantly depending upon the type of fiber, such as cellulose, pectin or a mix of various types. The variation in experimental design also complicated matters. According to the Food and Agriculture Organization of the United Nations, the reduction in the apparent digestibility of protein is typically less than 10 percent.
There are three possible explanations for the presence of undigested food protein in the digestive system: fiber can inhibit the work of enzymes that break down dietary protein; fiber can result in a direct reduction in the transit time of protein; and proteins within plant cells might be less accessible to digestive enzymes compared with proteins in animal cells. The excretion of nitrogen might also be the result of factors other than undigested protein. For example, fiber intake stimulates bacterial growth, increasing nitrogen output.