A little fiber history
Fiber became a household word back in 1970s when Dr. Denis Burkitt, a man nicknamed the Fiber Man, and his colleagues made "the fiber hypothesis" that states that fiber can prevent certain diseases. Through their work in Africa, they discovered that diseases that were common in the Western cultures were not common there. These included heart attacks and high blood pressure (cardiovascular diseases), obesity and diabetes (metabolic disorders), intestinal problems (constipation, diverticulosis, diverticulitis, gallstones, appendicitis, hemorrhoids, polyps, and colon cancer), varicose veins and blood clots (deep vein thrombosis). The primary dietary difference was the high intake of fiber and low intake of refined carbohydrates in the African population. Burkitt also noted the emergence of these diseases in the United States and England after 1890 following the introduction of a new milling technique that removed fiber from whole grain flour to produce white flour.
While the exact mechanism by which fiber might prevent these diseases remained unknown, Burkitt made a discovery about the beneficial impact that fiber had on bowel movements and how that related to certain diseases. Burkitt noted that he was able to predict the number of a patient's hospital visits from the size and frequency of their bowel movements. Those with high intakes of fiber had more frequent and bulky stools and had less illness. Burkitt proposed that fiber's health benefits stemmed from its ability to increase stool bulk and speed up how quickly stool moves through the colon. Since these findings, controversy remains. A great deal of research has both supported and disputed what Burkitt had discovered.
What is fiber?
A variety of definitions of fiber exist. In an attempt to develop one definition of fiber that everyone can use, the Food and Nutrition Board assembled a panel that came up with the following definitions:
- Dietary fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. This includes plant nonstarch polysaccharides (for example, cellulose, pectin, gums, hemicellulose, and fibers contained in oat and wheat bran), oligosaccharides, lignin, and some resistant starch.
- Functional fiber consists of isolated, nondigestible carbohydrates that have beneficial physiological effects in humans. This includes nondigestible plant (for example, resistant starch, pectin, and gums), chitin, chitosan, or commercially produced (for example, resistant starch, polydextrose, inulin, and indigestible dextrins) carbohydrates.
- Total fiber is the sum of dietary fiber and functional fiber. It's not important to differentiate between which forms of each of these fibers you are getting in your diet. Your total fiber is what matters.
You may also hear fiber referred to as bulk or roughage. Call it what you want, but always remember that fiber is an essential part of everyone's diet. While fiber does fall under the category of carbohydrates, in comparison, it does not provide the same number of calories, nor is it processed the way that other sources of carbohydrates are.
This difference can be seen among the two categories that fiber is divided into: soluble and insoluble.
- Soluble fiber dissolves in water to form a gel-like substance. Sources of soluble fiber are oats, legumes (beans, peas, and soybeans), apples, bananas, berries, barely, some vegetables, and psylluim.
- Insoluble fiber increases the movement of material through your digestive tract and increases your stool bulk. Sources of insoluble fiber are whole wheat foods, bran, nuts, seeds, and the skin of some fruits and vegetables.
Fiber for weight control
There is some evidence that "bulking up" could lead to slimming down. In a recent study of more than 1700 overweight and obese men and women, those with the highest fiber intake had the greatest weight loss over 24 months. Results from the Continuing Survey of Food Intakes by Individuals (CSFII) from 1994 -1996 also supported the relationship between a high-fiber intake and lower body weight. One of the reasons that fiber may have an impact on body weight is its ability to slow the movement of food through the intestines. The gel-like substance that soluble fibers form when they dissolve in water causes things to swell and move slower in the intestines. This increase in time that foods stay in the intestines has been shown to reduce hunger feelings and overall food intake. It has also been shown to decrease the number of calories that are actually absorbed from the ingested food. One study showed an increase in the number of calories that were excreted in the stools when high-fiber psyllium gum-based crackers were given in comparison to low-fiber crackers. Whenever fewer calories are taken in, or more are excreted, weight loss will generally occur.
Fiber for controlling diabetes
A high-fiber diet may be just what the doctor ordered to get your blood sugars under control. Keeping our blood sugars stable is a goal that we would all benefit from. If you don't have type 2 diabetes, this could be the way to prevent it. If you do have it, this could be the way to keep it under control. The best time to address type 2 diabetes is before it has developed. Research has shown that high-fiber diets can help prevent this form of diabetes. The most recent study on done on overweight and obese men and women without diabetes showed reductions in blood sugar and insulin with the use of a high soluble fiber supplement. A German clinical trial reported that eating fiber-enriched bread for only three days improved insulin sensitivity in overweight and obese women by 8%. If a diet intervention this small can have that great of an impact, you can imagine what years of following a high-fiber diet, filled with vegetables, fruits and whole grains would do. The good news for those with diabetes is that increasing your fiber now can also prevent long-term complications from diabetes. Soluble fiber has been found to produce significant reductions in blood sugar in 33 of 50 studies testing it. In clinical intervention trials ranging from two to 17 weeks, consumption of fiber was shown to decrease insulin requirements in people with type 2 diabetes. If you have ever had to inject yourself with insulin, you can appreciate how much easier and less painful it would be to increase your fiber intake to avoid the need for insulin injections.
Fiber for preventing heart disease
If we were to sit down and have a "heart to heart," I would tell you that one of the best things that you could do on your own to protect your heart is to follow a high-fiber diet. Numerous studies have produced compelling evidence to support this. In a Harvard study of over 40,000 male health professionals, researchers found that a high total dietary fiber intake was linked to a 40% lower risk of coronary heart disease, compared to a low-fiber intake. Another study of over 31,000 California Seventh-day Adventists found a 44% reduced risk of nonfatal coronary heart disease and an 11% reduced risk of fatal coronary heart disease for those who ate whole wheat bread compared with those who ate white bread. One minor change in their diets provided a protective effect that could save their lives.
Another strong predictor of heart disease is abnormal blood cholesterol, LDL, and/or HDL levels. It appears that soluble fiber reduces the absorption of cholesterol in your intestines by binding with bile (which contains cholesterol) and dietary cholesterol so that the body excretes it. The oat bran and bean fiber intervention trials where dietary fiber supplementation was combined with a low-fat diet shows that reductions in total cholesterol levels ranged from 8-26%. Other studies have shown that 5 to 10 grams of soluble fiber a day decreases LDL cholesterol by about 5%. All of these benefits will occur regardless of changes in dietary fat. In a trial with low fat and low fat plus high fiber groups, the group consuming high fiber exhibited a greater average reduction (13%) in total cholesterol concentration than the low fat (9%) and the usual diet (7%) groups. It seems that you don't have to change everything to gain something.
Fiber for bowel disorders
"Roughing" up your diet can be the key to healthier bowels. With the introduction of white flour came an increased prevalence of bowel disorders such as diverticulosis, diverticulitis, hemorrhoids, polyps, colon cancer, and irritable bowel syndrome (IBS). In Burkitt's early research into this phenomenon, he made reference to the fact that the typical African stool specimen was large and soft, and that stool transit times were rapid, compared to the puny hard fecal deposits and slow transit times of Europeans. In one of his studies, they conducted elaborate experiments in which volunteers in England, India, and Africa had their bowel movements timed and their stools weighed. Among the results of the study: People living under primitive conditions, on diets high in insoluble fibers, passed from 2½ to 4½ times as much feces as sailors in the Royal Navy, and were relatively free of many of the diseases studied. Current research supports the early findings. Studies have shown that a high-fiber diet (particularly fruit and vegetable fiber) help to prevent diverticulosis and will decrease the risk of complications if you have it. Although the mechanism by which fiber may be protective against diverticulosis is unknown, several hypotheses have been proposed.
For example, some scientists report that fiber helps by decreasing transit time, increasing stool weight, and decreasing pressure within the colon. The same has been found for irritable bowel syndrome (IBS). The current guidelines for the treatment of IBS include following a high fiber diet. The bulk that fiber provides is thought to help prevent the painful spasms often associated with IBS and aid in comfortable regularity. There is still a great deal of debate about the role of fiber in preventing colon cancer. The studies that look for connections with people's diets and their health have seen a trend in low-fiber diets and people with colon cancer. The studies that tried to intervene by putting people on high-fiber diets in order to prevent colon cancer or polyps did not find the same protective relationship. Burkitt's work and a more recent study showed that a daily stool weight greater than 150 grams needs to be achieved for the protective affect against colon cancer. This was not taken into account in many of the studies and may be the reason the protective effect was not found.
Fiber for preventing or treating constipation
Fiber may just be the way to go when constipation is the problem. Although what constitutes constipation is not well established, diets that increase the number of bowel movements per day, improve the ease with which a stool is passed, or increase stool bulk are considered beneficial. Both soluble and insoluble fibers are necessary for regular bowel movements. Oftentimes, people use over-the-counter supplements to assist with regularity. Unfortunately, these supplements only provide soluble fiber. Studies support the benefits of the combination of soluble and insoluble fiber in alleviating constipation, but only with the consumption of an adequate fluid intake. High amounts of fiber, without fluids, can aggravate, rather then alleviate constipation. The way to go is to eat foods high in both soluble and insoluble fibers and drink lots of water to flush it down.
Fiber chart: Recommendations for fiber intake
The average American's daily intake of fiber is about 5 to 14 grams per day. The current recommendations from the National Academy of Sciences, Institute of Medicine are to achieve an adequate intake (AI) of fiber based on your gender and age. The AI is expected to meet or exceed the average amount needed to maintain a defined nutritional state or criterion of adequacy in essentially all members of a specific healthy population.
|19 to 30 years||38 g/d|
|31 to 50||38 g/d|
|51 to 70||30 g/d|
|19 to 30 years||25 g/d|
|31 to 50||25 g/d|
|51 to 70||21 g/d|
Some helpful hints about fiber
- Increase slowly: The best way to begin is to figure out how much fiber you are currently eating each day. Once you know your number, you can begin to slowly increase how much you are eating until you reach your recommended amount. Increasing too quickly can lead to gas, bloating, and/or diarrhea.
- Add the fluids: If you do not have enough fluids (preferably water) with your high-fiber diet, you may end with the problem that you are trying to avoid: constipation. Get into the habit of drinking a minimum of 2 cups of a calorie-free beverage between each meal and you will avoid any unwanted problems.
- Don't go overboard: More is not always better, so try not to eat more fiber than your body can comfortably handle. There is no Tolerable Upper Intake Level (UL) set for fiber, which means that there is no cap on how high you can go before it causes any damage. Pay attention to how your bowel movements are responding to your fiber intake, and speak with your physician if you have any questions.
- Little here, little there: You don't need to get all of your fiber in one meal. Be creative, and have sources of fiber throughout the day. Here are some ways to do this:
- Add flaxseeds, seeds, or nuts to your salad, soup, cereal, or yogurt.
- Keep frozen blueberries, strawberries, and raspberries in your freezer to add to cereal, dessert, shakes, or yogurt.
- Have cut-up veggies in small baggies available to take with you. Use them with a meal or as a snack.
- Choose cereal with a minimum of 4 grams of fiber in each serving; you can have it as a meal, alone as a snack, or with some yogurt.
- Beans and peas go with everything; put them in your salad, soup, or have them with your meals or snacks.
- Go for products with whole wheat flour. It may take a little while to get used to the taste, so be prepared to experiment with different products until you find the one that you like.
- Have veggies with your meals whenever possible. Anything that you add will count. The more variety, the more we eat, so have as many different veggies at one meal as you can.
- Use fruit with, or in between, your meals. Set a minimum number of servings to have each day and be sure to reach it. Always go for the fruit with the skin and/or seeds for the fiber.
There is nothing easy about developing new eating habits. It will take time and practice, so be patient as you learn to incorporate these suggestions into your diet. Use the information in this article to remind you of why these changes are worth the effort. If we are what we eat, it's time we become high-fiber people.
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Medically reviewed by Joseph Palermo, DO, American Osteopathic Board Certified Internal Medicine
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