Stop Ignoring Fiber

Why it matters for muscle composition.

The bodybuilding community has an intense focus on macronutrients: protein for muscle, carbohydrates for gaining mass. The conversation around protein is all about isolates-vs-concentrates and quick-vs-slow release. Meanwhile, the conversation around carbohydrates is all about glycemic index and simple-vs-complex carbohydrates. But a lot of bodybuilders ignore or undervalue one particular type of minimally-caloric carbohydrate that can actually have an immense impact on your fitness: FIBER. 

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We now know that eating fiber has profound positive effects on the body. The effects include: loss of fat in favor of muscle, weight loss as a result of reduced fat absorption, reduction of cholesterol leading to better heart health, and reduction of post-meal blood glucose level which will help prevent the onset of diabetes. Prior to the 1970s, we didn’t know all of this. The indigestible portion of food derived from plants was called “roughage.” No one realized it offered any tangible physiological advantages until researchers from Great Britain and South Africa published studies indicating that populations from underdeveloped countries, which consumed higher amounts of fibers than did those populations on “western diets,” had less chronic diseases, and had better body composition than did their western counterparts. Today, the WHO recommends consuming 20 to 38 grams of fiber per day depending on age, gender, and activity level. But what does this mean for people looking to build muscle and put on size? Why has fiber become an essential component in foods and nutritional supplements?

Fibers exist in all plant products, and help provide physical structure. In nature, soluble fibers are found in soybeans and other legumes, oats, barley, rye, apples and other fruits, nuts, broccoli, corn, carrots and other vegetables, among other sources. Insoluble fibers are found in whole grain foods, wheat, potato skins, and vegetables such as beans, cauliflower, and zucchini. Unlike other nutrients that are broken down into simple fats and sugars in the intestine (thus raising glucose, fat levels, and blood pressure), fibers cannot be broken down by intestinal enzymes; they enter the colon in an unchanged chemical form.

Recently technologies and processing techniques have allowed some natural fibers to be isolated, concentrated, and then modified to give them superior functional and physiological characteristics. Among these are soluble corn fiber, and “resistant starch.” It is these fibers that are typically added to nutritional supplements or energy bars to provide the healthy benefits of natural fibers.

Many plant compounds fall under the classification of “fiber,” and these compounds may be further classified as "soluble fiber" or "insoluble fiber," depending on how they act on the body. Ingestion of different types of fiber results in different metabolic and health benefits. "Insoluble fibers” such as bran slow down stomach emptying, which results in reduced hunger and modest weight loss at the expense of body fat to favor muscle preservation and growth. In recent studies, insoluble fibers have also been associated with regulating blood sugar, reducing blood pressure, reducing cholesterol by interfering with its absorption, and reducing the amount of dietary fat the body can absorb. Together, these effects reduce the potential for heart disease caused by a build-up of cholesterol and fat in the arteries.

"Soluble fibers," including resistant starch, soluble corn fiber, and other similar compounds called oligosaccharides, are broken down (fermented) to short-chain fatty acids by intestinal bacteria in the colon. These short-chain fatty acids are absorbed from the lower GI tract and provide fuels for the cells in the intestinal wall, thus maintaining the colon in a healthy state. Lack of soluble fiber will compromise these intestinal cells and may lead to intestinal diseases, including colon cancer. Additionally, and importantly, the fermentation results in the enhancement of intestinal bacteria, which are beneficial to the health of an individual, and a reduction in those bacteria that are not beneficial. This is the probiotic effect. This is important because these harmful bacteria have been associated with an increase in colon cancer. Additionally, some fatty acids formed by the fermentation of soluble fiber will be absorbed into the blood stream and are thought to provide energy for the building of new muscle. One of these fatty acids in particular – butyrate – has been associated with a whole host of metabolic benefits in recent animal research. Butyrate has been linked to higher fat oxidation and improved insulin tolerance, helping promote a lower body fat percentage.

So If you’re really serious about taking control of your nutrition, dig a little deeper into that nutrition label, go beyond basic carbs and protein – turns out the indigestible carbs are just as important for your health and performance as the digestible ones. Whatever dietary regimen you may be employing, whether you’re a serious bodybuilder, a “weekend warrior,” or a casual athlete, consuming an adequate amount of fiber (either from eating vegetables, fruits, cereals, or nutritional supplements and energy bars), will enhance your health, increase your performance on the field, in the squat rack, and throughout your life.

Ronald J. Amen holds a doctorate in nutritional physiology from Rutgers. He co-edited one of the very first books ever written on dietary fiber, "Topics in Dietary Fiber Research." Dr. Amen holds several patents in food, nutrition, and pharmaceuticals.


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