Adults need about 21 to 38 grams of fiber a day, depending on age and sex. That works out to 14 grams for every 1,000 calories you eat. Most people fall well short: the average American eats about 16 grams a day.
Key takeaways
Through age 50, women need about 25 grams a day and men about 38. From 51 on, it's 21 and 30 (NASEM).
Only about 5% of Americans reach the recommended amount (Dahl and Stewart, 2015).
People who ate the most fiber had a 15% to 30% lower risk of dying early and of dying from heart and blood vessel disease (Reynolds et al., 2019).
Add fiber slowly, over a few weeks, with plenty of fluids (MedlinePlus).
How much fiber do you need a day?
The National Academies set fiber at 14 grams for every 1,000 calories (Dahl and Stewart, 2015). By age and sex, that comes to (NASEM):
Ages 19 to 50 | 51 and older | |
|---|---|---|
Women | 25 grams | 21 grams |
Men | 38 grams | 30 grams |
The World Health Organization suggests at least 25 grams a day of fiber from food for adults (WHO, 2023).
How much fiber do most people get?
Far less. Americans eat about 16 grams a day on average (MedlinePlus), and only about 5% reach the recommended amount (Dahl and Stewart, 2015).
Why does fiber matter?
A review funded in part by the World Health Organization pooled 185 long-term studies and 58 trials. People who ate the most fiber had a 15% to 30% lower risk of dying early and of dying from heart and blood vessel disease than people who ate the least. They also had lower rates of heart disease, stroke, type 2 diabetes and colorectal cancer (Reynolds et al., 2019).
The drop in risk was largest at 25 to 29 grams a day, and the trend suggested more could help further. The trials also found lower body weight, blood pressure and cholesterol with more fiber (Reynolds et al., 2019). The disease findings come from studies that follow people over time, so they show a link, not proof. But the more fiber people ate, the lower their risk, which made the authors think fiber itself may be part of the reason.
Whole grains are a big part of the story. Every 90 grams a day of whole grains was linked to a 19% lower risk of heart disease in a review of 45 studies (Aune et al., 2016). For more on grains and sugar, see carbs and added sugar.
What's the difference between soluble and insoluble fiber?
Fiber comes in two main kinds, and most high-fiber foods have some of each. Soluble fiber, found in foods like oats, beans and some fruits, soaks up water and turns into a gel during digestion, which slows digestion down. Insoluble fiber, found in wheat bran, whole grains and vegetables, adds bulk and helps food move through your gut (MedlinePlus).
You don't need to count them separately. Eating a mix of whole grains, beans, fruits and vegetables covers both.
Does fiber help with blood sugar?
For people with diabetes or prediabetes, yes, over time. A review of 42 trials in adults with these conditions found that more fiber lowered HbA1c and fasting blood sugar. For adults with diabetes, the authors suggested adding about 15 grams a day, or reaching 35 grams, as a reasonable goal (Reynolds et al., 2020). HbA1c shows your average blood sugar over the past two to three months (MedlinePlus).
Right after a meal, it depends on the food. Across 80 trials, whole grains led to a modestly smaller rise in blood sugar after meals than refined grains, though some authors work for a cereal company (Sanders et al., 2023). Another review, also with industry-linked authors, found that foods made from ground whole wheat or rye didn't significantly lower the rise compared with their refined versions. Whole-grain rice did, compared with white rice (Musa-Veloso et al., 2018). There's more in blood sugar basics and walking after eating.
How do you add more fiber?
Slowly. Adding a lot at once can cause gas, bloating and cramps, so raise it over a few weeks. Drink plenty of fluids as you go, about 8 glasses of water or other drinks without calories a day (MedlinePlus).
The WHO suggests getting carbs mainly from whole grains, vegetables, fruits and pulses, such as beans, lentils and peas (WHO, 2023). Easy places to start:
Beans or lentils in a soup, salad or rice dish.
A whole grain in place of white bread or white rice.
Fruit or nuts as a snack.
Oats for breakfast a few days a week.
Frequently asked questions
Is 16 grams of fiber a day enough? It's well under the recommended amount for every adult group (NASEM), and it's about what the average American eats (MedlinePlus). Raising it slowly is a reasonable goal.
Do I need to count soluble and insoluble fiber separately? No. Most high-fiber foods have some of each (MedlinePlus), so a mix of whole grains, beans, fruits and vegetables covers both.
Can I eat too much fiber? Too much at once can cause gas, bloating and cramps, which is why adding it gradually helps (MedlinePlus). If you have a digestive condition, ask your doctor how much is right for you.
Do fiber supplements count? Some can help. In a review of trials, about 13 grams a day of thick, gel-forming fiber supplements lowered HbA1c by 0.58 percentage points in people with type 2 diabetes, on top of their usual care (Jovanovski et al., 2019). If you have diabetes, ask your doctor before adding one. Food also brings vitamins and other nutrients, so it's a good place to start.
How Knit shows your fiber
When you log food in an app connected to Apple Health, Knit shows your daily fiber in the Record tab, under Nutrition. The chart marks 28 grams, which is 14 grams for every 1,000 calories on a 2,000-calorie day.
