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 about 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. Much of 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 higher intake of fiber from all food sources is beneficial,” says Dr. Joanne Slavin, a nutrition scientist at the University of Minnesota.
Types of Fiber
Different types of fiber can affect your health in different ways. That’s why the Nutrition Facts labels on some foods may list two categories of fiber: soluble and insoluble.
Soluble fiber is found in oats, beans, peas, and most fruits. Insoluble fiber is found in wheat bran and some vegetables.
Some soluble fiber is broken down by the complex community of bacteria and other microbes that live in the human gut. These microbes, called gut flora or microbiota, help with our digestion.
Emerging research shows they can affect our health in various ways. Studies suggest that they may play a role in obesity, type 2 diabetes, colon cancer, and other conditions.
Researchers are now looking at how different types of dietary fibers affect the gut microbiota—and how that, in turn, affects our health.
But soluble and insoluble fiber aren’t always listed separated on labels. Many foods contain both. And both types have health benefits.
Experts suggest that men aim for about 38 grams of fiber a day, and women about 25 grams. Unfortunately, in the United States, we take in an average of only 16 grams of fiber each day.
Some of fiber’s greatest benefits are related to cardiovascular health. Several large studies have found that people who eat the most fiber had a lower risk for heart disease.
High fiber intake—particularly soluble fiber—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 heart disease, stroke, and high blood pressure,” says Dr. Somdat Mahabir, a nutrition and disease expert with NIH’s National Cancer Institute.
Fiber can help relieve constipation and normalize your bowel movements. Insoluble fiber is often used to treat or prevent constipation and diverticular disease, which affects the large intestine, or colon.
Fiber may also play a role in reducing the risk for type 2 diabetes, the most common form of diabetes. 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 an 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.
Your weight 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,” Slavin says.
Other large studies have found that people with high fiber intake tend to weigh less—although that may be because their diets are healthier.
Scientists have also looked into links between fiber and different types of cancer, with mixed results. For example, there is evidence that a high intake of dietary fiber may reduce the risk for colon cancer and colon polyps.
A Fiber-Rich Diet
Experts say that 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,” Mahabir says.
“The focus should be more on eating diets that are rich in whole grains, legumes, beans, vegetables, fruits, nuts, and seeds 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 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 soluble fibers, such as inulin, polydextrose, or maltodextrin. These isolated fibers are included in the product label’s list of ingredients.
However, the health benefits of isolated fibers are 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. They’ve also shown inconsistent effects on the regularity of bowel movements.
On the plus side, some studies suggest they might boost the growth of good bacteria in the gut.
The bottom line is that most of us need to fit more fiber into our day, no matter what the 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.
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