Fiber: how much you need and where to get it

Most adults need about 22 to 34 grams of fiber a day, depending on age and sex, under the 2020–2025 US dietary guidelines' rule of 14 grams per 1,000 calories.^{[26, 44]} The National Academies' figures run higher for men, at 38 grams up to age 50.^[25] The average US adult eats 16.6 grams.^[29]

How much fiber you need a day

Both main US targets, the 2020–2025 Dietary Guidelines and the National Academies, start from the same rule: 14 grams of fiber for every 1,000 calories you eat.^{[25, 26]} For a 2,000-calorie diet, that is 28 grams a day.^[27] They are based on the levels linked to a lower risk of coronary heart disease.^[26]

The targets differ because each one assumes a different calorie level. The Dietary Guidelines for Americans, 2020 to 2025, apply the rule to one reference calorie level per age group.^[26] The National Academies' adequate intake, set in 2005, assumes higher calorie needs for men.^[25]

During pregnancy, the National Academies' figure rises to 28 grams a day, and to 29 grams while breastfeeding.^[25] On Nutrition Facts labels, the Daily Value for fiber is 28 grams.^[28]

The newest edition, the Dietary Guidelines for Americans 2025 to 2030, says to "prioritize fiber-rich whole grains."^[30] Its scientific report cites an optimal intake of 25 to 29 grams a day of total fiber.^[31] The gram targets in the table above come from the 2020 edition and the National Academies.^{[26, 25]}

Why fiber matters

A 2019 review in The Lancet, with the World Health Organization among its funders, pooled 185 cohort studies and 58 trials.^[33] In the cohort studies, people who ate the most fiber had a 15 to 30 percent lower risk of early death, heart disease, stroke, type 2 diabetes and colorectal cancer than those who ate the least.^[33]

Those are associations. The authors say the links "could be causal", and rated the certainty as moderate.^[33]

The same review found the risk reduction was greatest at 25 to 29 grams a day.^[33] In its trials, higher fiber intake lowered body weight, systolic blood pressure and total cholesterol.^[33]

How big the benefit is remains open. A later review behind the 2025 to 2030 guidelines found a smaller link for type 2 diabetes, an 8 percent lower risk.^[31] A 2026 review of 113 trials on fiber and bowel habits notes that the best evidence-based fiber recommendations "have not been established."^[37]

Soluble and insoluble fiber

Soluble fiber

Fiber that attracts water and turns to gel during digestion, which slows digestion. It is found in oat bran, barley, nuts, seeds, beans, lentils, peas and some fruits and vegetables.^[32]

Insoluble fiber

Fiber that does not dissolve in water. It adds bulk to stool and helps food move through the gut. It is found in wheat bran, vegetables and whole grains.^[32]

Most high-fiber foods contain both kinds.^[32] Soluble fiber from certain foods helps lower LDL cholesterol as part of a diet low in saturated fat and cholesterol. The FDA allows a heart health claim for 3 grams or more a day of beta-glucan from whole oats or barley, or 7 grams or more of soluble fiber from psyllium husk.^[34]

In trials, a median 3.5 grams a day of oat beta-glucan lowered LDL cholesterol by 0.19 mmol/L.^[35] A median of about 10.2 grams of psyllium lowered it by 0.33 mmol/L.^[36]

The foods with the most fiber per portion

Every row below is one entry in USDA FoodData Central, the government's food composition database, and each food name links to it. All are from the SR Legacy data set. Portions are the household measures USDA lists for each food, a few of them scaled as the table caption explains.

Beans, lentils and peas fill much of the top of the list, alongside chia seeds and raspberries. A half cup of cooked navy beans, lentils or black beans gives 7.5 to 9.6 grams.^{[2, 5, 6]} The 2020–2025 US dietary guidelines note that swapping processed or high-fat meats for beans, peas and lentils raises fiber.^[26] They also give protein; see our ranking of high-protein foods.

In these pairs, the whole grain wins. A cup of cooked brown rice has 3.2 grams of fiber and a cup of white rice has 0.6.^{[20, 24]} A slice of whole-wheat bread has 1.9 grams and a slice of white bread has 0.8.^{[22, 23]} Whole fruit also beats juice: 100% fruit juice is lower in fiber than whole fruit.^[26]

Closing the gap: a worked example

A day of food with more calories needs more fiber under the same rule. If you track calories, our guide to calories and macros explains the rest of the plate, and how to count macros shows how to log it.

How to add fiber without stomach trouble

• Go slowly. Eating a lot of fiber in a short time can cause gas, bloating and cramps. It often goes away as the gut bacteria adjust.^[32]
• Drink fluids. Water helps fiber pass through the digestive system. MedlinePlus suggests about 8 glasses of water or noncaloric fluid a day.^[32]
• Eat the peel. Taking the peels off fruits and vegetables lowers the fiber you get.^[32]
• Mind the minerals at very high intakes. Too much fiber may interfere with the absorption of iron, zinc, magnesium and calcium. This is usually not a big concern, since high-fiber foods tend to be rich in minerals.^[32]

No upper limit has been set for fiber.^[25] The National Academies noted one may be needed if foods with added fiber became widespread.^[25]

Fiber supplements versus food

The FDA treats fiber that is naturally part of foods like vegetables, whole grains and fruit as beneficial without further proof.^[43] Isolated or added fibers count on a label only when the FDA has found a health benefit.^[43] The 2019 Lancet review left out supplement trials, so its findings are about fiber from food.^[33]

Supplements do have a role. NIH lists fiber supplements as one option a health care professional may suggest for constipation for a short time.^[42] Psyllium has its own trial evidence for LDL cholesterol, shown above.^[36]

When to talk to a clinician