When you think of dieting, you probably either think about cutting calories, fat, carbohydrates, or eating substandard tasting foods. However, few consider the advantages to incorporating fiber into their diet. If this is uncharted territory for you, fiber is a nonessential complex carbohydrate that is indigestible by humans. Although it is nonessential, fiber is still recognized as an important component of your diet.
Dietary fiber has many advantages such as its ability to induce feelings of satiety, delay gastric emptying, lower cholesterol, reduce transit time in the colon, and reduce the glycemic response to certain foods. I'll go over these benefits in more details so that you can become more familiar with each one. But first, I'm going to go through and give some background information on fiber so the bigger picture will make more sense in the end.
What makes fiber indigestible to humans is the inability of our enzymes to breakdown certain carbohydrates, even though they may consist primarily of glucose (like most carbohydrates). The reason that our enzymes cannot breakdown fiber is due to its chemical structure, which is determined by the conformation of the bonds between glucose units.
In other words, the packing of the molecule can restrict access of enzymes to the bonds they normally breakdown. Believe it or not, bananas and potatoes are almost completely resistant to digestive enzymes and reach the colon relatively intact!
There are seven major categories of fibers including cellulose, hemicellulose, pectic substances, gums, mucilage, algal polysaccharides, and lignin. Cellulose is the most common of these fibers, and can be found in the plant cell wall. Hemicelluloses are fibers that contain 5 and 6 carbon sugars. Pectic substances are water-soluble fibers rich in galacturonic acid. Gums are actually substances secreted by plants in response to injury. Mucilages are also water-soluble, and are used by plants to protect seeds. Algal polysaccharides are extracted from algae. Finally, lignin is found in woody plants.
The Different Catogories Of Fibers
Physiologically, fiber can be categorized as soluble and insoluble. On nutrition labels, you will often see amounts of soluble and insoluble fiber in the carbohydrate section. So what's the difference? Generally, cellulose, lignin, and some hemicelluloses are insoluble and nonfermentable. On the other hand, pectins, gums, mucilages, and the other hemicelluloses are soluble and fermentable. I'll explain what these terms mean later, but as a preview, the soluble fibers will more than likely make you pass gas, which is what fiber is famous for.
If you've ever eaten a large portion of beans or vegetables, you've probably noticed that you feel really full, and that your stomach seems like it sticks out further than normal (gastric distention). Since fiber is resistant to digestion in the stomach, the bulk that fiber adds to a meal produces feelings of fullness that can last for a long period of time. So, if you are reducing your caloric intake and still feel hungry after you eat, try incorporating some soluble fiber with your meals.
Also, soluble fibers form gels in the stomach and therefore slow gastric emptying. This results in a more uniform presentation of your meal to the small intestine for absorption. Since insoluble fibers do not form gels in the stomach, they have no effect on the rate of gastric emptying. Again, if you are getting hungry between meals when dieting, soluble fibers will help the food move slower from your stomach to your small intestine. This will keep you feeling fuller longer.
One drawback of soluble fiber intake is that the gel that is formed in your stomach can entrap other nutrients like other carbohydrates, proteins, and fats. This prevents enzymes needed for nutrient absorption from reaching the entrapped nutrients. By eating higher levels of protein and fat, this effect may be normalized. However, this entrapping effect of soluble fibers is also beneficial in that it improves glucose tolerance and lowers blood cholesterol. By improving glucose tolerance, blood glucose levels are lowered following meals with soluble fiber, the glycemic response of carbohydrates is then lowered, and thus insulin secretion is also lowered.
Insulin is one of the major anabolic hormones, and if its levels are decreased, your catabolic diet will be more successful. For diabetics, decreasing blood glucose after a meal is obviously beneficial because the need for insulin is not as high as it normally would be. Thus, increasing the intake of soluble fiber can be used as a preventative and treatment method for diabetics.
The Effects Of Fiber
The effect of fiber on blood cholesterol is still being investigated. However, researchers believe that the mechanism by which fiber may lower blood cholesterol is multifactorial. By delaying gastric emptying, fiber affects the rate of lipid absorption, which influences lipoprotein formation, thus reducing the amount of cholesterol in the blood following a meal.
Since the gel formation caused by soluble fiber interferes with digestive enzymes, lipid absorption is impaired, and therefore lipoprotein formation is impaired. Fibers may bind to the bile acids or interfere with micelle formation, impairing the absorption of cholesterol (bile acids and micelles are needed for cholesterol absorption).
Once fiber reaches the large intestine, propionate is produced, enters the blood, and can inhibit cholesterol biosynthesis. This all may seem a little hairy, but if you do a little researching on how cholesterol is formed from fats, it will make a little more sense.
Within the colon (the large intestine), the ability of fiber to reduce transit time depends on whether or not it is soluble. Soluble fibers are more readily fermented by bacteria in the colon than are insoluble fibers. Therefore, more of the insoluble fiber remains in the feces, creating much more bulk than do the soluble fibers. Said another way, taking in more insoluble fiber increases the size of your feces than does soluble fiber. The increase in bulk also increases the amount of water-holding capacity within the feces. The combination of greater mass and greater moisture content contributes to a decrease in transit time within the colon.
How Much Fiber Should I Have?
Presently, there is no recommended dietary allowance for fiber. However, it is suggested that individuals take in 10 to 13 grams of fiber for every 1000 calories. The concentration of fiber in the diet should be increased with age, because energy requirements decline in older individuals. Food sources of fiber include whole grain products, legumes, leafy vegetables, and some fruits such as apples, oranges, prunes, and raspberries.
As you can see, including fiber in your diet has positive consequences for individuals trying to lose fat, preparing for a physique contest, or trying to improve their health status. Much more research must be performed before the real value of dietary fiber can be fully realized, but the results thus far are very promising. Feel free to e-mail me with any questions!