Fiber is comprised of components of plant materials (long chain glucose molecules) that are resistant to human digestive enzymes. Fiber plays an important role in digestion, providing bulk, decreasing bowel transit time, absorbing toxins and cleaning the colon of mucus and undigested food particles. Fiber acts to increase the thickness of the stomach contents which gives a feeling of fullness and slows down the emptying of the stomach. Later in the process, as fiber moves through the system its bulk enables food to pass more quickly through the bowels while it absorbs toxins, excess bacteria and mucus in the intestines and contributes to easier and more normal bowel movements.

Fiber comes in two forms — soluble and insoluble. Soluble fiber absorbs up to 15 times its weight in water as it moves through your digestive tract, producing softer stools. It's most abundant in oats, legumes and fruits. Insoluble fiber, found in vegetables and whole grains, gives stool its bulk. Softening and bulking of stool helps to prevent constipation, some types of diarrhea and symptoms of irritable bowel syndrome. These actions also decrease pressure in the intestinal tract, reducing the risk of hemorrhoids and diverticular disease (a condition in which pouches form in the intestinal walls). Unfortunately many people don’t get enough fiber. Americans typically consume 10 to 15 grams of fiber with most dietary guidelines recommending twice that amount. This correlates with bowel transit times of up to 96 hours, more than twice what it should be (12 to 24 hours). The solution is increasing fiber intake to recommended levels through diet or fiber supplements or a combination of the two.

Fiber and Colon Cancer

In addition to its obvious benefits in speeding and improving digestion and elimination there is a growing body of research indicating that fiber has an important role in the prevention of cancer. Results from the largest scientific study investigating the relationships between diet and cancer risk strongly support the role for dietary fiber in the prevention of colon cancer, according to the American Institute for Cancer Research (AICR) and the World Cancer Research Fund International. Results from the European Prospective Investigation into Cancer (EPIC) study were published in the British journal The Lancet. Researchers tracked the diets of 519,978 subjects in ten European countries for an average of 4.5 years.

They found that those subjects who ate the most dietary fiber (averaging 35 g/day) had their risk of colon cancer reduced by 40 percent, compared with subjects who ate the least fiber (averaging 15 g/day. An American study published in the same issue of The Lancet used a different method but reached a similar conclusion. In this case-control study, researchers with the Prostate, Lung, Colorectal and Ovarian Cancer Screening project team (PLCO) compared the fiber intakes of 33,917 subjects without colon adenomas (non-malignant polyps) to 3,591 subjects with at least one polyp. Those subjects who ate the most dietary fiber (more than 30 g/day) had their risk of polyps reduced by 20 percent, compared to those who ate the least (less than 15 g/day).

One factor that makes the EPIC study so unique in the field of diet-cancer research is the number of subjects it is currently tracking - over half a million individuals, aged 24-75. Another important strength of the project is its ability to compare the widely different diets of 10 European countries - Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden and the UK. The enormous dietary variation among these countries means that diet-cancer associations are easier to identify. In an editorial discussing the EPIC and PLCO studies, the Lancet concludes, "…eating a diet rich in plant foods, in the form of fruit, vegetables and whole-grain cereals probably remains the best option for reducing the risk of colon cancer, and for more general health protection."

Increasing Fiber Intake

Some suggestions to increase dietary fiber include:

• Increase grain intake to 6 to 11 servings a day. These include cereals, breads, rice and pasta. High-fiber cereals are one of the easiest to find sources as one serving size can be as high as 8-10 grams of fiber. Whole-grain breads, brown rice and wheat bran effectively incorporate fiber.
• Vegetables (3 or more servings a day) are an excellent source of fiber, especially broccoli, cabbage, cauliflower, corn, green beans, tomatoes and zucchini.
• Fruits (at least 2 servings per day) including apples, bananas, apricots, grapes, peaches, and strawberries and replace processed fruit juice with whole fruit.
• Limit dairy products to 2 to 3 servings or less.
• Limit poultry, seafood and meat to no more than 3 servings.
• Legumes can be used as a high protein, low fat alternative to animal foods. These include beans, dried peas and lentils.
• Use fats, sweets and alcohol sparingly.
• Many nuts are high in insoluble fiber.

Ideally your daily intake of fiber should be between 30-40 grams. Since it’s not always possible to get this amount through diet alone fiber supplements and meal replacers with fiber can be added to the diet. When choosing fiber supplements its important to limit soluble fiber supplements (bulking, psyllium based laxatives) since they extract water from the intestines and cause dehydration and constipation.