What You Need to Know About Fiber

The term fiber refers to carbohydrates that cannot be digested. Fiber is present in all plants that are eaten for food, including fruits, vegetables, grains, and legumes. Current recommendations suggest that children and adults consume at least 20 grams of dietary fiber per day from food, not supplements. The more calories you eat each day, the more fiber you need; teens and men may require upwards of 30 to 35 grams per day or more.

Fiber seems to reduce the risk of developing various conditions, including heart disease, diabetes, diverticular disease, and constipation. Despite what many people may think, however, fiber probably has little, if any effect on colon cancer risk. For years Americans had believed this was the case, but after better designed and larger studies the evidence does not support this. 

High intake of dietary fiber has been linked to a lower risk of heart disease in a number of large studies that followed people for many years.  Heart disease is the leading cause of death for both men and women in the United States.  Fiber intake has also been linked with the metabolic syndrome, a constellation of factors that increases the chances of developing heart disease and diabetes. These factors include high blood pressure, high insulin levels, excess weight (especially around the abdomen), high levels of triglycerides, the body's main fat-carrying particle, and low levels of HDL (good) cholesterol. Several studies suggest that higher intake of cereal fiber and whole grains may somehow ward off this increasingly common syndrome.

Type 2 diabetes is the most common form of diabetes. It is characterized by sustained high blood sugar levels. It tends to develop when the body can no longer produce enough of the hormone insulin to lower blood sugar to normal levels or cannot properly use the insulin that it does produce. There are several important factors that may help lower your risk for type 2 diabetes, such as maintaining a healthy weight, being physically active, and not smoking. Researchers are also trying to figure out any relevant dietary factors, one of which seems to be a high-fiber diet. When it comes to factors that increase the risk of developing diabetes, a diet low in cereal fiber and rich in high-glycemic-index foods (which cause big spikes in blood sugar) seems particularly bad.

One question raised by such studies is whether fiber itself protects against heart disease and diabetes, or whether the disease-fighting benefits accrue from the nutrient-rich whole grain package. A recent meta-analysis of seven major studies showed that cardiovascular disease (heart attack, stroke, or the need for a procedure to bypass or open a clogged artery) was 21 percent less likely in people who ate 2.5 or more servings of whole grain foods a day compared with those who ate less than 2 servings a week.  Another meta-analysis of several large studies, including more than 700,000 men and women, found that eating an extra 2 servings of whole grains a day decreased the risk of type 2 diabetes by 21 percent.  So to protect against heart disease and diabetes, perhaps the best advice is to choose whole grain, high-fiber foods at most meals.

Diverticulitis, an inflammation of the intestine, is one of the most common age-related disorders of the colon in Western society. In North America, this painful disease is estimated to occur in one-third of all those over age 45 and in two-thirds of those over age 85. In a long term follow-up study, eating dietary fiber, particularly insoluble fiber, was associated with about a 40 percent lower risk of diverticular disease.

The good news is that the gastrointestinal tract is highly sensitive to dietary fiber, and consumption of fiber seems to relieve and prevent constipation.The fiber in wheat bran and oat bran seems to be more effective than similar amounts of fiber from fruits and vegetables. Experts recommend increasing fiber intake gradually rather than suddenly. As fiber intake is increased, the intake of beverages should also be increased, since fiber absorbs water.