Dietary Fiber

Key takeaways

• Guideline basis: 14 g per 1,000 calories eaten
• Women 19-50: about 25-28 g a day
• Most useful single change: Swap white bread, rice and pasta for whole-grain versions of the same meal.
• Commonest mistake: Doubling your intake in one day, which reliably causes bloating and gas.
• See a doctor if any of the signs under "When to get help" below apply to you.

Why it matters

Higher intakes are linked to lower rates of heart disease, type 2 diabetes and colorectal cancer, yet more than 90 percent of women and 97 percent of men in the US fall short of the recommendation.

The numbers, in one place

Published figures for Dietary Fiber

Measure	Figure
Guideline basis	14 g per 1,000 calories eaten
Women 19-50	about 25-28 g a day
Men 19-50	about 31-34 g a day
Daily Value on food labels	28 g
Richest everyday sources	beans, peas and lentils, whole grains, vegetables, fruit, nuts

What helps

• Swap white bread, rice and pasta for whole-grain versions of the same meal
• Leave the skins on potatoes, apples, pears and carrots
• Keep canned beans, chickpeas and lentils in the pantry
• Add fiber gradually over a few weeks and drink more fluid as you do, since fiber works by holding water

What to avoid

• Doubling your intake in one day, which reliably causes bloating and gas
• Fiber supplements when food can do the job more cheaply
• Assuming "multigrain" means whole grain; check that the first ingredient says whole

In depth

Fiber is not one substance but a family of plant compounds that resist digestion in the small intestine. Two broad types behave differently. Soluble fiber, found in oats, barley, beans, apples and citrus, dissolves in water to form a gel that slows digestion. Insoluble fiber, found in wheat bran, whole grains, nuts and vegetable skins, holds onto water and adds bulk, helping stool move through the gut. Most plant foods contain a mix of both, which is one reason a varied diet works better than a single fiber source.

The gel formed by soluble fiber does useful work. It slows how quickly sugar from a meal reaches your bloodstream, which smooths out blood glucose. It also binds bile acids in the gut; your liver then pulls cholesterol from the blood to make more, which is how oats and beans help lower LDL cholesterol. Insoluble fiber, meanwhile, makes stools larger and softer, which is why it helps prevent constipation and the straining linked to hemorrhoids.

When fiber reaches the colon, much of it becomes food for the trillions of bacteria that live there. They ferment it into short-chain fatty acids, which nourish the cells lining the colon and appear to influence inflammation and metabolism. This is an active area of research, and much is still unknown, but it helps explain why fiber-rich diets are linked to better health in ways that go beyond regularity. It also explains the gas: fermentation produces it, and your gut bacteria need time to adjust.

Signs and symptoms

• Constipation, with hard, dry or infrequent stools
• Straining on the toilet, which can lead to hemorrhoids
• Feeling hungry again soon after meals
• Larger swings in energy after refined, low-fiber meals
• Bloating and gas when fiber is increased too quickly, which usually settles in a few weeks

Causes and risk factors

• Diets built around refined grains such as white bread, white rice and regular pasta
• Few beans, lentils, vegetables and whole fruits in everyday meals
• Relying on juice, which removes most of the fiber found in whole fruit
• Heavily processed snacks and fast food, which are usually low in fiber
• Low-carbohydrate diets that cut whole grains, fruit and beans along with refined carbohydrate
• Peeling fruit and vegetables, since much of the fiber is in or just under the skin

How it is checked

There is no blood test for fiber intake. The simplest way to assess it is to look at what you eat over a few typical days, either with a food-tracking app or by reading Nutrition Facts labels, and compare the total with your target. A registered dietitian can review a food diary with you and suggest swaps that fit your budget and tastes.

If you are troubled by bowel symptoms, your doctor will look at the whole picture rather than assume low fiber is the cause. They may ask about your diet, fluid intake, medicines and family history, and may suggest tests such as blood work, a stool test or a colonoscopy if there are warning signs or if you are due for colorectal cancer screening, which USPSTF recommends from age 45.

Related topics

• Cooking with Pulses: What the Evidence Actually Says (Healthy Recipes)
• Gut Health and Immunity: What the Evidence Actually Says (Immunity)
• Bloating: Sorting the Evidence From the Noise (Digestive Health)
• Carbohydrates and Blood Glucose: Sorting the Evidence From the Noise (Diabetes)

Where to go next

• Dietary Fiber, Explained Without the Jargon
• A Working Checklist for Dietary Fiber
• Nutrition: The Complete Guide
• Dietary Protein: What the Evidence Actually Says
• The Evidence on Dietary Salt, Without the Hype

When to get help

See your doctor rather than adding fiber if you have a change in bowel habits lasting three weeks or more, blood in your stool, unexplained weight loss or ongoing abdominal pain, and take advice from your own care team if you have inflammatory bowel disease or a known stricture. Call 911 for severe abdominal pain with vomiting, a swollen belly and no bowel movements or gas.

Where this comes from

• Dietary Guidelines for Americans — Dietary Guidelines for Americans, 2020-2025
• MedlinePlus — Dietary fiber

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.