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Life Extension Magazine

New Findings on Fiber

May 2005

By Stephen Laifer

Natural Cancer Weapon

Medical researchers estimate that 30-40% of all cancers are preventable by lifestyle and dietary measures alone. Fiber-depleted processed foods are viewed as significant contributors to excess cancer risk.36

Recent studies have examined the role of a high-fiber diet—typically supplying more than 34 grams of fiber a day—in preventing cancer. Most of these studies have focused on colorectal cancer. A high-fiber diet reduced the risk for rectal cancer by a remarkable 56% in one study, while eating more that three servings a day of whole-grain products was associated with a 31% reduced risk. By contrast, consumption of refined grain products in excess of 4.5 servings a day was associated with a 42% greater risk of rectal cancer.37 A similar study by a consortium of health groups, including the National Cancer Institute, showed that high intake of vegetables, fruits, and whole-grain foods—all high in dietary fiber—reduces the risk of distal colon adenomas (precancerous growths of the colon). Patients who consumed the most fiber had a 27% lower risk of adenomas than those who consumed the least fiber.38

The 2003 European Prospective Investigation into Cancer and Nutrition (EPIC) was the largest study ever to investigate the association between diet and cancer risk. Spanning 10 countries, the EPIC study followed 519,978 participants, aged 24 to 75, for nearly five years. The study results indicate that abundant intake of dietary fiber is highly protective against colorectal cancer. Participants who consumed the most dietary fiber had a 40% lower risk of developing colon cancer than those who ate the least fiber. The study authors proposed that if populations with a low average dietary intake of fiber doubled their fiber consumption, they could slash their risk of colorectal cancer by 40%.39

The Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial compared the fiber intake of 33,971 patients who tested negative for polyps to 3,591 patients who had at least one verified adenoma in the distal large bowel. The study found that patients consuming the most fiber had a 27% lower risk of adenomas than those who consumed the least fiber. Interestingly, the researchers further noted that fiber “might serve as a marker for unmeasured substances that have anti-carcinogenic effects.”40

Diabetes and Insulin Control

The obesity epidemic in America has dramatically increased the incidence of type II diabetes by exacerbating insulin resistance.41 For those who have tried unsuccessfully to lower cholesterol with a high-carbohydrate, low-fat diet, refined carbohydrates that are low in fiber may be to blame.

Refined, fiber-depleted carbohydrates tend to have a high glycemic index, and thus cause a rapid increase in blood sugar. Following their consumption, a “glucose spike” prompts the pancreas to release insulin, which in turn signals the liver to pump more triglycerides into the bloodstream. Dietary fiber slows the absorption of food so that blood sugar does not rise as rapidly, while also reducing insulin secretion.42 This was demonstrated in a study published in 2004 in which a high fiber intake led to improved glycemic control, along with reduction of blood pressure and serum cholesterol and triglyceride levels.43

Fiber’s positive effects on blood glucose and insulin concentrations are most evident in people diagnosed with diabetes mellitus. In a randomized study, researchers compared the effects of a diet high in fiber (50 grams/day) to those of a moderate-fiber diet (24 grams/day) recommended by the American Diabetes Association. They found that a high intake of dietary fiber, particularly soluble fiber, significantly improves glycemic control, decreases hyperinsulinemia (a disorder associated with aberrant blood sugar control), and lowers plasma lipid concentrations in diabetic patients.44

In one study, guar gum improved metabolic control and decreased serum lipids of nine patients with type II diabetes.45 In another promising research trial, three weeks of supplementation with guar gum lowered both fasting and after-meal blood glucose levels. In addition, the attenuation of insulin levels suggests that guar gum slowed the rate of carbohydrate absorption. Cholesterol levels dropped 14% on average in the diabetic subjects.46 Thus, supplementation with soluble fibers like guar gum appears to improve glycemic control and lipid profiles in people with type II diabetes.

Selecting the Best Fibers

Dietary fibers, which are resistant to digestion by enzymes in the gastrointestinal tract, can be classified as either water soluble or insoluble. Soluble fiber in particular helps lower cholesterol levels by binding to cholesterol in the intestinal tract and increasing its elimination from the body. Good sources of soluble fiber include beans, peas, rice bran, oats, barley, citrus fruits, and strawberries. Adding two to three servings of high-fiber fruit or cereal could provide powerful added protection for your heart.

Oat bran and oatmeal, both of which contain the fiber beta-glucan, have been the subject of growing attention.47 In 1997, the FDA approved the health claim that “a diet high in soluble fiber from whole oats and low in saturated fat and cholesterol may reduce the risk of heart disease.”48 Researchers have debated beta-glucan’s mechanism of action in the body. While some speculate that beta-glucan may act as a physical barrier in the intestinal tract by blocking the absorption of bile acids and cholesterol, others have theorized that soluble fibers are bacterially fermented in the colon, leading to the production of short-chain fatty acids that may lower cholesterol synthesis.49

According to a German study published in 2004, different sources of dietary fiber confer various benefits.50 Food sources of dietary fiber like whole-grain bread, vegetables, and fruit are particularly useful in preventing and treating colon conditions and cancers. Purified dietary fibers such as cellulose, guar gum, psyllium, and beta-glucan help promote healthy blood sugar levels. All water-soluble fibers help maintain normal blood lipid levels, according to the study authors, but oat bran is especially effective.

The Importance of Fiber Supplements

The average American currently consumes only 12-17 grams of fiber a day from dietary sources, far below the 20-35 grams recommended by the American Dietetic Association and the 30 grams or more suggested by both the American Heart Association and the National Cancer Institute.51,52

Since many people do not want to change or cannot change their diets, supplements and natural fiber products can help them benefit from fiber’s many beneficial effects. Supplemental fiber products can provide optimal combinations and amounts of fiber, as well as complementary nutrients such as calcium. Incorporating increased fiber intake into a daily plan for healthy living can help you lower your risk of heart attack and cancer, as well as prevent or manage such common conditions as hypertension and diabetes mellitus. Moreover, fiber is a valuable tool in achieving optimal weight.

With increased fiber intake, some people may experience gastrointestinal discomfort or changes such as increased or loose bowel movements. This is simply the body’s period of adjustment to the introduction of greater amounts of dietary fiber. Medical professionals recommend adding fiber to the diet gradually until the body adjusts. Moreover, because soluble fibers form a gel with water, it is important to drink plenty of water with fiber supplements. Abundant water intake will help to optimize fiber’s actions in the body and prevent ill effects such as dehydration or constipation.


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