Fiber—you know it's good for you. But if you're like many Americans, you don't get enough. In fact, most of us get less than half the recommended amount of fiber each day.
Dietary fiber is found in the plants you eat, including fruits, vegetables, and whole grains. It's sometimes called bulk or roughage. You've probably heard that it can help with digestion. So it may seem odd that fiber is a substance that your body can't digest. It passes through your digestive system practically unchanged.
"You might think that if it's not digestible then it's of no value. But there's no question that a higher intake of fiber from all food sources is beneficial," says Dr. Joanne Slavin, a nutrition scientist at the University of Minnesota.
Fiber can relieve constipation and normalize your bowel movements. Some studies suggest that high-fiber diets might also help with weight loss and reduce the risk for cardiovascular disease, diabetes, and cancer.
The strongest evidence of fiber's benefits is related to cardiovascular health. Several large studies that followed people for many years found that those who ate the most fiber had a lower risk for heart disease. The links between fiber and cardiovascular health were so consistent that these studies were used by the Institute of Medicine to develop the Dietary Reference Intakes for fiber.
Experts suggest that men get about 38 grams of fiber a day, and women about 25 grams. Unfortunately, in the United States, we take in an average of only 14 grams of fiber each day.
High fiber intake seems to protect against several heart-related problems. "There is evidence that high dietary fiber consumption lowers 'bad' cholesterol concentrations in the blood and reduces the risk for developing coronary artery disease, stroke, and high blood pressure," says Dr. Somdat Mahabir, a nutrition and disease expert with NIH's National Cancer Institute.
Fiber may also lessen the risk for type 2 diabetes, the most common form of diabetes. The fiber in the intestines can slow the absorption of sugar, which helps prevent blood sugar from spiking. "With diabetes, it's good to keep glucose levels from peaking too much," explains Dr. Gertraud Maskarinec of the University of Hawaii.
In a recent NIH-funded study, Maskarinec and her colleagues followed more than 75,000 adults for 14 years. Consistent with other large studies, their research found that diabetes risk was significantly reduced in people who had the highest fiber intake.
"We found that it's mostly the fiber from grains that protects against diabetes," Maskarinec says. However, she notes that while high fiber intake may offer some protection, the best way to reduce your risk of diabetes is to exercise and keep your weight in check.
Weight loss is another area where fiber might help. High-fiber foods generally make you feel fuller for longer. Fiber adds bulk but few calories. "In studies where people are put on different types of diets, those on the high-fiber diets typically eat about 10% fewer calories," says Slavin. Other large studies have found that people with high fiber intake tend to weigh less.
Scientists have also looked into links between fiber and different types of cancer, with mixed results. Much research has focused on colorectal cancer, the second-leading cause of cancer death nationwide. Protection against colorectal cancer is sometimes stronger when scientists look at whole-grain intake rather than just fiber. One NIH-funded study of nearly 500,000 older adults found no relationship between fiber and colorectal cancer risk, but whole-grain intake led to a modest risk reduction.
Different types of fiber might affect your health in different ways. That's why the Nutrition Facts Panels on some foods list 2 categories of fiber: soluble and insoluble. Soluble fiber may help to lower blood sugar and cholesterol. It's found in oat bran, beans, peas and most fruits. Insoluble fiber is often used to treat or prevent constipation and diverticular disease, which affects the large intestine, or colon. Insoluble fiber is found in wheat bran and some vegetables.
Still, experts say the type of fiber you eat is less important than making sure you get enough overall. "In general, people should not be too concerned by the specific type of fiber," says Mahabir. "The focus should be more on eating diets that are rich in whole grains, vegetables, and fruits to get the daily fiber requirement."
Whole grains, fruits, and vegetables are also packed with vitamins and other nutrients, so experts recommend that you get most of your fiber from these natural sources. "Unfortunately, a lot of people tend to pick low-fiber foods. They go for white bread or white rice. Most of the processed foods—foods that are really convenient—tend to be low in fiber," says Slavin.
For people who have trouble getting in enough fiber from natural sources, store shelves are filled with packaged foods that tout added fiber. These fiber-fortified products include yogurts, ice cream, cereals, snack bars, and juices. They generally contain isolated fibers, such as inulin, polydextrose, or maltodextrin. These isolated fibers are included in the product label's list of ingredients.
The health benefits of isolated fibers are still unclear. Research suggests they may not have the same effects as the intact fibers found in whole foods. For instance, there's little evidence that isolated fibers help lower blood cholesterol, and they have differing effects on regularity. On the plus side, some studies suggest that inulin, an isolated fiber from chicory root, might boost the growth of good bacteria in the colon.
The bottom line is that most of us need to fit more fiber into our day, no matter what its source. "It would be great if people would choose more foods that are naturally high in fiber," Slavin says.
Increase your fiber intake gradually, so your body can get used to it. Adding fiber slowly helps you avoid gas, bloating, and cramps. Eat a variety of fruits, vegetables, whole grains, and nuts to add a mix of different fibers and a wide range of nutrients to your diet. A fiber-rich diet can help your health in many ways.
