The facts on fiber - Harvard Health

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Harvard Health

Think you eat enough fiber? Think again. Adults should eat 14 grams of fiber for every 1,000 calories consumed. This is 28 to 34 grams of fiber per day for most men. However, most eat less than half that amount, according to the Dietary Guidelines for Americans 2020–2025.

Why so little? Blame poor food choices, says Dr. Walter Willet, a professor of epidemiology and nutrition at Harvard's T.H. Chan School of Public Health. "People eat more ready-to-eat processed foods, which are made from refined grains stripped of fiber, such as white rice and white flour and found in pasta, pastries, cakes, and crackers."

Changes in eating patterns also play a role. As people age, they often need fewer calories. Eating less further cuts down on their fiber intake. Also, many fiber-rich foods require more chewing than other foods, which can be difficult for some older adults.

The two types

There are two types of fiber: soluble and insoluble. Soluble fiber pulls water from the stomach, turning the fiber into a gel. This slows digestion and makes you feel full after eating. It also helps soften stools. In comparison, insoluble fiber doesn't dissolve in water. It adds necessary bulk to stool, preventing constipation.

But fiber has other health benefits. Research has found that a high-fiber diet lowers LDL (bad) cholesterol levels and is linked with lower incidences of cardiovascular disease, cancer, and diabetes.

Studies also have discovered that adequate fiber can also alter the gut microbiome to support the immune system and protect against inflammation. High levels of dietary fiber also may help reduce the risk of developing dementia, according to a study published in 2023 in Nutritional Neuroscience.

Finding fiber

There are many high-fiber foods from which to choose, so there is a good chance you can find many to add to your diet. Examples include fruits, vegetables, legumes, nuts, seeds, and whole grains. (You can find a list of fiber-rich foods at /fiber.)

Men can get their necessary daily fiber from two to four servings of fruit; two to five servings of vegetables, whole grains, or legumes; and one to two servings of nuts and seeds. But don't get bogged down in tracking exact fiber amounts for each meal or worrying about eating enough of both fiber types. "Keep it simple, and just focus on eating a variety of fiber-rich foods and avoiding refined grains," says Dr. Willett. However, it's fine to start by eating only one or two of your favorite high-fiber foods. "If you love blueberries, have two daily servings of just those," says Dr. Willett. "Gradually, you can add other fiber foods."

The role of supplements

Over-the-counter fiber supplements come in capsules, powders to be mixed with water, and chewable tablets. Common brands include Benefiber, Metamucil, Citrucel, and Konsyl. Are they ever a good option? If you have trouble eating fiber-rich foods — due to food sensitivity or difficulty chewing high-fiber foods — these can occasionally be used to increase your fiber, according to Dr. Walter Willett of Harvard's T.H. Chan of Public Health. "Some people also may benefit from a supplement if they suffer from constipation due to medication or follow a low-carbohydrate diet for health reasons," he says. "However, supplements should never replace a healthy diet as your primary source of fiber, as they don't provide the valuable micronutrients you get from high-fiber foods." If you think you may benefit from a fiber supplement, speak with your doctor.

Small changes

Another approach is to make small changes to your eating habits. For example, commit to eating beans, lentils, or peas at least three times a week. Switch out regular pasta for versions made from whole wheat, quinoa, chickpeas, or lentils.

Replace white rice with whole grains like brown rice or bulgur. "Something simple like starting your day with a bowl of steel-cut oatmeal is also a good beginning," says Dr. Willett. "I top mine with some yogurt, nuts, and in-season fruit, which adds variety along with more fiber."

Be careful about too much fiber in a race to increase your daily intake. "Your digestive system can't always tolerate a lot of fiber at one time, which can lead to gas, bloating, diarrhea, and stomach cramps," says Dr. Willett. "Take it slow, and make sure to drink plenty of water daily as you increase your fiber."