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All About Dietary Fiber

All About Dietary Fiber


It isn't absolutely necessary to begin a discussion of dietary fiber with a review of diverticular disease, but that's the way this one begins because it was a bout with diverticulitis that inspired in me a curiosity about and a newfound appreciation for dietary fiber. You can start your article on dietary fiber any way you want-this is how I'm starting mine.

Attentive readers will recall that last Saturday (that's August 4, 2007 for the benefit of future historians) found me doubled over in pain in the emergency room of my local hospital. The stomach cramps that had motivated my visit to this place I rarely visit unless I absolutely have to were diagnosed as diverticulitis, and after a detailed explanation of the condition, its causes, and its remedies by the avuncular Doctor Jordan, I was sent away with a prescription for oral antibiotics and stomach cramps that were identical in every way to those I had when I entered the hospital.

Fortunately the pains in my lower gut abated after a couple of dosages of Ciproflaxin, thus allowing me to attain something resembling an upright posture enough to sit at my computer and do some internet-based research on the malady that had cut me down. As I have said before, I like to learn something new every day because, by the end of most days, I've usually forgotten two or three things, and in the course of several hours spent at the websites of several well known hospitals and medical schools, I learned enough about diverticulitis to cover my quota of forgotten things for at least a month or two.

The first thing I learned about diverticulitis is that it has to do with things called diverticula (that's the plural of diverticulum). These diverticula are abnormal sacks or pouches that form on the outside of the lower intestine. (Actually, they can form on many other organs as well, but it's the ones on the lower intestine, or colon, that interest us here.) Picture the bubble formed by a bicycle inner tube when it protrudes through a hole in the tire and you have a pretty good idea of what they are and how they are formed. The presence of these diverticula constitutes a condition called diverticulosis, and when one of these diverticula becomes infected or inflamed, that is the condition known as diverticulitis. Collectively, all these things plus several other complications are known as diverticular disease.

I was astonished to learn that in the United States (which apparently is the world headquarters for diverticular disease although it is also quite popular in England, Canada, and Australia), diverticular disease is basically a man-made condition. The disease was first recognized around 1900, and it is no coincidence that refined wheat flour (i.e. flour with the fiber removed) was introduced in industrialized nations around the same time. The disease is rare in Asia and Africa where the typical diet contains large amounts of fiber.

I was further astonished to learn that more than 50 percent of Americans over the age of 60 have diverticula, and that percentage increases with age. That's the bad news. The good news is the majority of the people who have diverticula never know it, and unless they experience a bout of diverticulitis like I did, the likelihood is they will never be bothered by it.

My grandfather had diverticulosis for all of the years that I knew him, and my mother and I recall very well the many restrictions the condition placed on his diet and on the people who cooked for him. After doing a little research I was astonished yet again by how much of what I thought I knew about diverticulosis was wrong.

When my grandfather was diagnosed with diverticular disease over fifty years ago, his doctor made him swear off a plethora of foods. He was told to reduce his fiber intake (in those days it was referred to as "roughage"), so just about all fruits and vegetables were on his list of foods to avoid. He was specifically warned away from small seeds such as sesame, poppy, and caraway seeds, and from fruits and vegetables containing small seeds such as berries, tomatoes, peppers, and cucumbers. He was told to stear clear of the skins of fruits and vegetables, all types of nuts, and could eat beans only if they were strained to eliminate the skins. As if this diet weren't limiting enough, he was further cautioned that spices of all sorts could cause a relapse of his condition. All of these things were considered potential obstructions which could block or clog a diverticulum and cause infection and inflammation.

I was greatly relieved to learn, upon researching the latest medical thinking on the subject, that the advice my grandfather received over fifty years ago was just as outdated as you would expect fifty-year-old advice to be, and this really came as no surprise to me.

What did come as a surprise was the number of readers who, in writing to offer their sympathies because they had also suffered from diverticular disease, revealed that they were still receiving the same outdated, old-fashioned dietary advice that my grandfather had received. I know that what I am about to tell you will be met with skepticism by some, but if you'll bear with me I will provide you with some unimpeachable sources to support what I am going to say, so please hold off on sending your nastygrams until you've read what the Mayo Clinic, the National Institutes of Health, and others have to say on the subject. Please.

I'll get right to the point: the current medical thinking is that there is no need to eliminate seeds (sesame, poppy, caraway) or fruits and vegetables with small seeds (berries, tomatoes, cucumbers) from your diet if you have suffered an attack of diverticulitis and are trying to prevent a recurrence. Ditto for nuts, skins of fruits and vegetables, and everything else my poor grandfather was prohibited from eating for a large portion of his life.

I know that many readers have been told otherwise by their doctors, and I would never suggest that you ignore your doctor's advice, but consider the possibility that your doctor might not be 100 percent up-to-date on this matter. And whatever you do, don't just take my word for it.

I urge my fellow diverticulitis sufferers to do what I did and search for articles on the web using your favorite search engine, and don't forget to put on your skeptic's hat when judging the reliability and trustworthiness of the many articles you will find. Personally, I'm a sucker for websites run by governmental agencies, university medical schools, and famous hospitals when it comes to medical advice. I am equally dubious of sites with names like "" which also happen to sell some miracle cure-all for every ailment my colon and I might one day experience. Be your own judge, but please don't let yourself be misled by websites that prey on the gullible.

The following websites are a few that I found to have reliable, up-to-date, and unbiased information on diverticular disease:

Diverticulitis diet: Should I avoid nuts and seeds?

Diverticulosis and Diverticulitis-National Digestive Diseases Information Clearinghouse (National Institutes of Health)


Diverticulitis-Medline Plus Medical Encyclopedia (National Institutes of Health)

I hope that readers interested in diverticular disease for whatever reason will check out these websites, and I also hope that they will use them as a starting point for their own investigation into the causes and treatments of the disease.

If you did your homework like good boys and girls and reviewed the websites on diverticular disease that I provided above, then you might have noticed the same thing I noticed when I first began educating myself.

I learned that the principal reason that diverticula form in the first place is a lack of sufficient fiber in the diet. Insufficient dietary fiber also leads to the painful and potentially dangerous inflammation of the diverticula known as diverticulitis. The primary treatment for diverticulitis is usually an increase in dietary fiber (although in some extreme cases your doctor might recommend a liquid diet low in fiber in order to give the large intestine a rest while it recuperates), and those of us who are not eager to have a recurrence of diverticulitis are encouraged to increase our intake of dietary fiber.

When I learned all this I scratched my head and said to myself, "My goodness my gracious me. Dietary fiber seems to be at the very root of diverticular disease. Fiber is not only the single best remedy for this painful and debilitating condition, but it is also the prophylactic measure prescribed to forestall recurrences of this insidious gastrointestinal malady. I must begin a thorough and detailed investigation of the role of fiber in the diet forthwith."

Sheesh, I never realized I was such a pedantic bombast even when talking to myself. Oh well. It is befitting a grandiloquent and excessively florid examination of any subject to begin with a definition of the matter at hand, and so I will begin this examination of dietary fiber. Here is the definition of dietary fiber offered by the American Association of Cereal Chemists:

Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plant substances. Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation.

Whew, that's quite a mouthful, but there are several important facts we can extract from this definition. First, dietary fiber comes from plants, and only from plants. (Okay, so there is some dietary fiber in mushrooms, and technically they're fungi and not plants, but let's call them plants for now, okay?) There is no dietary fiber in animal products such as meats, milk or dairy products, or eggs. None. Not even a little. Period.

Second, the part about being "resistant to digestion and absorption in the human small intestine" means that they pass through our digestive system essentially unchanged. This is why dietary fiber used to be called "bulk" and "roughage," and you may still encounter those terms being used today.

Third, the part about "complete or partial fermentation in the large intestine" means that bacteria that reside happily in our large intestines are able to break down dietary fiber to some degree even after our digestive system has given it its best shot and failed, and some of the byproducts of this fermentation may have significant health properties. More about this later.

Fourth, the business about "polysaccharides, oligosaccharides, lignin, and associated plant substances" is pure gobbledygook to me, so we'll just ignore that part.

Finally, the part about "laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation" is just a fancy way of saying that dietary fiber has health effects that go beyond helping to prevent and protect against diverticular disease as we have already discussed. We'll talk more about this later, too.

So, now that we have carefully analyzed the definition of dietary fiber, I'll bet you're still wondering just what the heck it is. Am I right?

Okay, let's take this nice and slow. I think that we all understand that dietary fiber is the parts of plants that our bodies are unable to digest, right? Well, it turns out that dietary fiber is divided into two categories: insoluble and soluble, and all foods that come from plants contain a combination of both these types of fiber in different proportions. Let's take a look at both of them.

Insoluble fiber is the one most familiar to us. It is the "roughage" and "bulk" that people usually think of when they think of dietary fiber. Although there are many types of insoluble fiber found in plant foods, the best known is cellulose, and in addition to being a primary component of the plant foods we eat, it is also the major component of grass clippings, sawdust, and your favorite pair of denim jeans. It is indigestible even to animals that rely on it for the majority of their diet including ruminants such as cows and sheep, and only the activity of bacteria in the digestive system prevents these animals from starving to death on a diet composed primarily of cellulose and other insoluble fibers.

Soluble fiber is a little harder to visualize. It might help to note that another word for soluble fiber is mucilage, and that one of the many compounds included in this category of dietary fiber is a group of chemicals known as pectins, the clear, gelatin-like compounds that make fruit jams and jellies semi-solid. Rather than the tough chewiness characteristic of insoluble fiber, soluble fiber is characterized by a slimy consistency, and this property accounts for the slippery texture of many foods that are high in soluble fiber such as oats and barley.

Now that we finally understand what dietary fiber is, I bet you are asking, "Why the heck do we need fiber in our diets?" I thought you would never ask.

Dietary fiber plays many important roles in helping us stay healthy, and as you might expect, the different types of fiber play very different roles.

Insoluble fiber adds bulk to the contents of the intestines and helps move the byproducts of digestion rapidly through the digestive tract. This provides a benefit in that some of those byproducts are downright toxic, and the faster your body gets rid of them, the better. A diet high in insoluble fiber also helps reduce constipation, one of the factors contributing to diverticular disease.

Soluble fiber tends to thicken the contents of the intestines, thus slowing the formation and release of those same nasty toxins. It also plays a role in preventing heart disease and type 2 diabetes through some rather complicated chemical processes. For our purpose, it is sufficient to think of it in terms of the soluble fiber absorbing some of the cholesterol and sugar in the foods we eat and allowing them to be excreted rather than absorbed into the blood stream. (This is a gross over simplification, but I'm just not smart enough to provide a more technical explanation. Sorry about that.)

For many years dietary fiber was touted as a preventative against colon cancer, but several large studies have recently failed to demonstrate a link between colon cancer and fiber intake. However, the other health benefits are well documented, and just because a diet high in fiber will have little or no effect in preventing colon cancer, there are still plenty of good reasons to pay attention to your fiber consumption.

Speaking of fiber consumption, just how much fiber are we supposed to consume anyway? The good news is that we don't really need a heck of a lot of fiber in our diets to keep the Fiber Police away from our doors. I mean, it's not like that old myth about having to drink 8 glasses of water every day. (See "All About Water" for more about that.) The bad news is, most of us aren't getting enough.

Depending on gender and age, it is recommended that most people consume between 21 and 38 grams of total fiber per day. (For the amount recommended for you, see this chart.) Unfortunately, the average American only consumes about 12 grams per day, and unless you are a vegetarian or eat a traditional African or Asian diet, the same is most likely true for you regardless of where you live.

There are a few fairly simple strategies to increase the amount of fiber in your diet, and I will elucidate those in a minute, but I think one of the best ways to increase your fiber intake is to learn more about the fiber content of various foods so that you can take the reins of your diet and begin increasing your fiber intake immediately. This is why I'm going to do something I have never done before: I'm going to give you a homework assignment.

Go to your favorite search engine and do a search to see what information you can find on the fiber content of various foods. Try to find a website or two that lists a large number of foods along with their fiber content, and be sure to bookmark them for future reference. See if you can find a list that contains amounts of soluble and insoluble fiber as well if you want extra credit. And remember, copying your neighbor's answer will get you a visit to the principal's office.

One of the things I hope we learned from out little homework assignment is that increasing our intake of dietary fiber doesn't have to be the chore that some modifications to our diet might be. For example, let's say that you really like artichoke hearts, and in the process of doing some research into dietary fiber on the internet you learned that artichoke hearts are very high in fiber (they are, you know?) So now it's just a matter of eating more artichoke hearts than you have in the past. There, wasn't that easy?

Here are some other easy strategies you can use to increase your intake of dietary fiber:

- Switch to whole-grain breads and pastas whenever possible. Eat brown rice instead of white rice, and eat more whole grains such as wild rice, quinoa, barley, and oats. And don't forget that corn in every form (except hominy or pozole) from fresh on the cob to stoneground cornmeal is a whole grain, so eat more polenta and cornbread.

- Eat more legumes of all kinds, including beans, lentils, split peas, green peas, garbanzos, and peanuts.

- Snack on fresh fruits and vegetables instead of potato chips and cookies.

- Eat a whole-grain cereal for breakfast, but be sure to keep an eye on the rest of the ingredients. Just because Lucky Charms are made with whole grains doesn't make them an intelligent choice.

- Berries of all kinds, and especially blackberries, raspberries, and strawberries are excellent sources of fiber, so eat more of them.

- Ditto for dried fruits such as figs, apricots, dates, raisins, and prunes.

- Nuts are a very good source of fiber, and although they are high in "good" fats, it's still fat no matter how you look at it, so eat them in moderation.

- All vegetables are rich in dietary fiber, but leafy greens such as kale, collards, and spinach are especially good sources. So are broccoli, Brussels sprouts, carrots, and beans in their pods such as green beans (haricots), snow peas (mange touts), and sugar snaps. All types of winter squashes are very high in fiber, and onions and artichokes are especially high in soluble fiber.

- The edible skins of fruits such as apples, pears, plums, and peaches, and vegetables such as potatoes, sweet potatoes, eggplants, tomatoes, cucumbers, and summer squash are excellent sources of insoluble fiber, so you can stop peeling them now.

Before we wrap up our discussion of dietary fiber, I think now is the time to offer a couple of caveats.

As we have seen, dietary fiber is by definition those parts of plants that pass through our digestive system virtually untouched. Therefore, dietary fiber contributes no calories to our diets and need not be considered by those who are trying to lose or maintain weight by counting calories. (In fact, consumption of fiber can result in a full feeling and might help some people stick to their diets by reducing hunger.)

We should keep in mind that dietary fiber (both the insoluble and soluble kinds) absorb water and prevent some of it from entering the blood stream during digestion. Accordingly, any increase in dietary fiber consumption should also be accompanied by an increase in fluid intake. A diet high in fiber with insufficient liquid in the digestive tract can result in constipation, one of the things we are trying to avoid by eating more fiber.

Nutritionists also recommend that, when switching from a low-fiber diet to a high-fiber one, the change should be done gradually in order to avoid taxing the digestive system with a sudden increase in mass.

As long as we increase our intake of dietary fiber in a reasonable and sensible manner, there is really very little we have to watch out for. Obviously, if you switch to a diet consisting of nothing but hay, you can expect to die from malnutrition eventually if the intestinal blockage doesn't kill you first, so I would strongly advise a consultation with your physician before starting on an all-hay diet, or any other radical change in your eating habits. In short, unless you are under doctor's orders to limit the amount of fiber in your diet, the words to remember are "fiber is our friend."

About all that remains to be said about dietary fiber is the same thing I caution against in all my essays: don't take my word for anything.

It's not that I would intentionally mislead you. Au contraire, I go to great lengths to ensure that the information I pass along to you in the form of my "All About" essays is as reliable, accurate, and up to date as possible. However, whenever I run across a pedantic bombast who is handing out free advice, I hear whatever I... er, I mean "he" has to say with a skeptical ear. I hope you do the same.

Please us the following links as a starting point for your own investigations into the nature and importance of dietary fiber. After you've studied up on the subject, I'm sure you will agree that fiber is our friend.

Additional reading:

Fiber-Harvard School of Public Health

Nutrition Fact Sheet: Dietary Fiber-Northwestern University Feinberg School of Medicine

Dietary fiber: An essential part of a healthy diet-Mayo Clinic

High-Fiber Foods-Mayo Clinic

Fiber 101: Soluble Fiber vs Insoluble Fiber

Dietary Fiber Database


Copyright © 2008 Worldwide Recipes. All rights reserved.

About "The Chef"
Joe BarksonJoe Barkson has been writing and publishing under the pen name "The Chef at Worldwide Recipes" since 1998. He came to food writing late in life following checkered careers in computer marketing, graphic design, and teaching high school Spanish. A lifelong interest in food and cooking ("I've been eating since I was a baby," he is fond of saying) was nurtured by extensive international travel during his formative years, and this accounts for the emphasis on world cuisine in his choice of recipes and themes. Twice married and currently happily single, he lives in rural Georgia with a hyperkinetic schipperke that answers to Cooky when the mood strikes him.


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