What We Now Know About Food Fiber
During my years in practice, I was a firm advocate of increasing food fiber in the diet. I was aware of the work of researchers in Africa who discovered that rural Africans who consumed a largely plant based diet with lots of fiber had 2-3 large, soft bowel movements a day. In addition, they seldom had diseases of the colon that are so common in the Western world. A high fiber diet made sense to me and many of my patients were relieved of constipation and simply felt better on such a diet. Further, some epidemiologic studies (including heart disease and cancer) began to show health benefits when fiber was significantly increased in the diet. Still, it seemed that this was the end of the fiber story. Little did I know!
There are many types of fiber that have been discovered in plants, including various types of starches, lignins, cellulose and others. These were of interest to plant chemists, but not to physicians. Then in the 1980s, it was discovered that fiber could broadly be separated into insoluble and soluble types. No fiber is digested by the small intestine. All of it arrives into the colon unchanged. Insoluble fiber does not dissolve in water, is not fermented or broken down by colon bacteria, but does retain lots of water in the colon and so provides a larger, softer stool. Soluble fiber, on the other hand, is broken down and fermented by colon bacteria. We really didn’t know too much more about these two types of fiber until the 1990s when better measuring methods were devised. In the last 15 years, the difference between these two fibers, insoluble and soluble, has become increasingly important, especially with the discovery of prebiotic soluble fibers.
The History of Fiber
At one time before farming occurred and animals were domesticated, our ancestors wandered around, eating berries, fruits, root vegetables and any plant that promised to have some nutrition. The diet contained 50-100 grams of fiber a day, all of it from plant material. Interestingly, one of the best studied prebiotics fibers, inulin, has been found in over 36,000 plants, so these people were eating a lot of this beneficial fiber.
Then came villages with farming, growing grains, and raising livestock. Fiber intake gradually diminished. Furthermore, in Westernized countries, fiber was removed from the grains as it was felt to be useless. We were left with white bread without fiber and many of the minerals and vitamins. The food industries also began boxing and packaging food products in ways that required further changes to basic foods . Many substances were added to prolong shelf life and enhance taste but they did not contribute to health as far as we knew. High fructose corn syrup was found to be as sweet as sugar and replaced it in many drinks and foods, as it was much cheaper. This corn derivative and other sweeteners were used in many products and have resulted in or are associated with the epidemic of obesity we now see in our society. Food fiber was side-lined as an important factor in the diet.
What is Prebiotic Fiber?
There are two basic types of food fiber – insoluble fiber, which does not dissolve in water and is not fermented by the gut’s bacteria, and soluble fiber, which does dissolve in water and is fermented by the colon’s microorganisms or bacteria. Almost all plant food, which is where fiber comes from, will have some of each but in different proportions. For instance, wheat is about 90% insoluble fiber. Oats are 50/50 and the psyllium plant is mostly soluble fiber. All of the above have been well-known for some time. In addition, it has been long known that in societies that consume large amounts of plant foods each day, such as in many rural African societies, that the general bowel health of the population is very good, and that the incidence of many disorders of the lower GI tract are almost non-existent. These include bowel irregularity, diverticulosis, colon cancer and polyps, Crohn’s disease and ulcerative colitis. We did not know exactly how or why this was occurring although it was obvious that the plant based diet was important.
Then in the mid 1990’s, medical researchers and nutritionists began to discover something quite remarkable about some soluble fibers. They found that certain soluble fibers such as inulin, oligofructose and FOS (fructo-oligosaccharide) caused some remarkable changes in the bacterial mix of the colon. They had discovered prebiotics.
Prebiotic fiber comes from plants such as the Jerusalem artichoke, chicory root, onions, whole grains, bananas and garlic. These essential soluble fibers do more than help people who ingest them in adequate amounts stay regular; multiple studies demonstrate that prebiotic fiber can favorably change the bacterial mix in the lower gut. For most of the 20th century, medical schools taught doctors that the bacteria that live in the human body were harmless; we now know that some of these bacteria actually perform important health functions. These functions include strengthening the bowel wall, improving the body’s ability to absorb essential nutrients such as calcium, producing the hormones that control appetite and anxiety, and more. The fact is that medical science is just at the beginning of a new world of exciting lower gut health discoveries.
Fiber has made a comeback, however. By its very definition, fiber is not digested and broken down in the small intestine. Rather, it moves on down into the colon. In the 1970s and 80s, we learned that there were two major types of fiber – insoluble fiber and soluble fiber. Insoluble fiber is not acted on or fermented in the colon. It provides no nutrition to the bacteria there. It does, however, hold lots of water and, in so doing, helps to get a softer, more regular bowel movement. Soluble fiber, on the other hand, is used by colon bacteria as a food source.
Another major development has been an understanding of the dramatic and major role that bacteria within the colon play in maintaining good health. In short, we benefit enormously from the bacteria in our colon. The soluble fibers, called prebiotics, provide the most benefits. These are health fibers. While there are many “candidate” prebiotics fibers, just a few have been studied to the extent that researchers and physicians understand what they can do and feel confident in recommending foods and supplements that contain prebiotic fibers.
Insoluble Fibers and You
When trying to figure out how you can add more fiber to your diet, the research is coming so fast and furious that it’s hard to know what to do. The good news is that adding dietary fiber in the form of non-digestible carbohydrates is easier than ever before. Here’s what you need to know about resistant starch, inulin-soluble fiber, oligofructose and why making small, manageable changes to your dietary lifestyle can reap more health benefits than you ever thought possible.
Soluble and Insoluble Fibers
Medical scientists and nutritionists categorize dietary fiber into two classifications. Soluble fiber, as the name suggests, dissolves easily in water. Plants such as beans, greens and other complex carbohydrates contain soluble fiber; some foods, such as the potato, contain a mix of insoluble fiber (the peel) and soluble fiber (the flesh underneath). The human body breaks down these complex carbs into a gelatinous, viscous byproduct that the large intestine turns into gases and acids that encourage the growth of beneficial bacteria in the lower gut. These bacteria positively affect several essential bodily functions and overall health.
Insoluble fiber won’t dissolve in water but is just as important to overall health and well being as soluble fiber. We can further classify insoluble fiber into two types: fermentable and non-fermentable. Non-fermentable insoluble fiber is known primarily as a bulking agent, and consuming adequate insoluble fiber keeps people regular. Fermentable insoluble fiber — such as resistant starch —produces the same healthy gases and acids in the large intestine that soluble fiber does. One important difference between the two types of fibers is that soluble fiber tends to slow digestion while insoluble fiber speeds it up.
Entering the dietary fiber mix is resistant starch, considered a third type of fiber that provides the benefits of both insoluble and soluble fibers. The term “resistant” refers to this starch’s ability to resist digestion. Instead, it passes to the large intestine where it produces the same effects of soluble and insoluble fibers. Although the terms are complex, you probably eat resistant starch and other fibers in your diet every day — food such as seeds, unprocessed whole grains, legumes and potatoes all contain resistant starch. People sometimes avoid eating starches because they fear weight gain; however, eating suitable amounts positively affects health in several ways.
These resistant starch foods help people stay fuller longer because they are not as easily digested. That means people who eat resistant starches (even unknowingly) are more likely to consume less calories over the course of one day. Also, resistant starch helps people burn fat while avoiding fat storage, according to several studies; it also boosts metabolism. Natural resistant starch foods also help diabetics manage their condition by decreasing glycemic response and increasing insulin sensitivity. It increases the growth of healthy bacteria in the lower gut, just like its fermentable soluble and insoluble fiber cousins. Still more research suggests that resistant starch contributes to digestive, brain, kidney and eye health.
How Much Fiber Do I Need?
The last 15 years have seen an incredible amount of research demonstrating the importance of fiber to overall health. Fiber-rich foods aren’t hard to find, either — green vegetables, whole grains, nuts, fruit, beans and supplements all provide excellent sources of prebiotics. Unfortunately, most Americans don’t eat nearly enough fiber-rich foods, according to WebMD. On average, adults consume about 15 grams of dietary fiber every day — sound like a lot? It isn’t, considering women and men should consume between 25 and 38 grams per day, respectively. And people who have an aversion or allergy to certain foods, such as wheat, have an even more difficult time ingesting their daily requirement.
To put these numbers into perspective, consider how much fiber is contained in the average serving size of common foods such as bananas, cereal and almonds. Eat a whole-grain bran cereal for breakfast and consume only 5 grams of fiber. Add a banana to your bowl and reap another 3 grams. Ready for a mid-morning snack of 24 almonds? You just added 3.3 grams of fiber, according to WebMD. The point is, eating enough fiber can’t be left to chance — making it a habit requires consciously eating fiber at every meal, because getting to a minimum of 25 grams takes a lot of careful planning.
The Easy Alternative
There is another alternative to planning each meal with military-like consistency. Prebiotic supplements that contain fermentable insoluble fibers such as inulin and oligofructose contain enough plant fiber to make securing your daily intake much easier. Another added benefit? All-natural prebiotic supplements such as Prebiotin are low in calories, don’t impart an offensive taste or texture on foods and provide all the same benefits that whole food prebiotics do — without the planning, math and potential weight gain.
Regardless of how you choose to add non-digestible carbohydrates to your diet, get in the habit of reading every label before you make a purchase — because now more than ever before, you are what you eat.