Fiber-rich foods can help lower calorie intake and slow nutrient absorption.
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Absorption occurs after digestion, a process that involves the breakdown of large food particles into smaller nutrient particles your body can use for its overall metabolism. Only three groups of nutrients can provide your body with energy, or calories: carbohydrates, protein and fats. Fiber is a carb that derives from plants and promotes digestive health. However, it differs from other carbs in that humans do not have the enzyme machinery to digest it.
Digestion begins in your mouth, with salivary enzymes breaking food down as you chew. The food material then transits to your stomach and bowels, where nutrient absorption occurs. Small, hairlike projections called villi line the inner walls of your small intestine. Each villus is in turn covered with smaller projections called microvilli. As digested foods pass through your intestine, villi and microvilli provide a large surface area for nutrient absorption. This absorption requires specific cells to facilitate the transport of nutrients from your small bowel into your bloodstream. Once in your bloodstream, nutrients can be transported to different parts of your body for storage, use or further processing.
There are two types of dietary fiber: water-soluble and insoluble. As its name suggests, water-soluble fiber can dissolve in water, while insoluble fiber cannot. In your bowel, soluble fiber pulls in water and forms a gel-like substance that slows the passage of food. As a result, nutrient absorption slows down, leading to lower blood glucose and cholesterol levels. Insoluble fiber primarily works like a broom. It softens and adds bulk to your stool to maintain bowel regularity. Fruits and oat bran contain soluble fiber, while insoluble fiber abounds in whole grains, nuts and wheat bran. Beans and many vegetables are rich in both fiber types.
Fiber and Calorie Absorption
Since fiber is indigestible, it remains relatively unchanged as it transits through your bowel and leaves your body in feces. Fiber's indigestible nature means your body cannot use it to derive energy for its metabolic activities. High-fiber foods not only need to be chewed for a long time, but they give you a sensation of fullness and provide fewer calories than fiber-poor foods. Feeling full reduces calorie intake, while a lower calorie content reduces the number of calories available for absorption in your bowel. Fiber-rich diets might therefore play a role in weight loss, according to the Colorado State University Extension.
While dietary fiber reduces your calorie absorption, a number of absorption disorders can do the same. Absorption disorders are simply conditions that decrease your body's ability to absorb nutrients from the food you eat. One example is lactose intolerance, which affects nearly 25 percent of the U.S. population, according to diet.com. Another example, celiac disease, involves intolerance to gluten , a protein present in barley, wheat and rye.