You know fiber is good for you. You know you’re supposed to eat it, but what exactly is fiber? Why is it so important, and how much should you eat per day? We’re going to make this easy for you by laying out everything you need to know, including simple tips for increasing your fiber intake.

Spoiler alert: You have full permission to slowly increase your fiber intake. If you are a low fiber consumer to begin with, you may experience occasional gas, bloating, and cramping while your gut acclimates to additional fiber in your diet. This should go away once your gut has adapted.

What Is Fiber and Why Is It Important?

Fiber is a complex carbohydrate that comes from plant foods like fruits, vegetables, legumes, and whole grains, but unlike other carbohydrates, fiber can not be broken down or absorbed by the body. This means it moves through the body undigested. [1] That’s good for digestive health because, let’s just say, it helps move things along (more on that later).

But that’s not all. As Stanford University Associate Professor of Microbiology and Immunology Justin Sonnenburg says, “Fiber is more than a bulking agent.” [2] Certain types of fiber act as the fuel for the microbes that live in our gut. A study conducted by Sonnenburg in 2016 suggests that consuming less fiber may mean fewer microbes in the gut. [3] Conversely, more fiber equals more gut microbes and better gut health.

There are two kinds of fiber: soluble and insoluble fiber. Both are important.

Soluble Fiber

Soluble fiber is found in various foods, including oats, nuts, seeds, beans, lentils, apples, and citrus. When it interacts with water, soluble fiber turns into a gel-like substance that moves through the stomach and small intestines slowly. [4] Why is this a good thing? Studies have shown that consuming soluble fiber can help maintain healthy glucose levels and cholesterol already in the normal range. [5]

Insoluble Fiber

Equally as important is insoluble fiber, which is found in foods like whole grains, legumes, most vegetables, fruits, nuts, and seeds. Insoluble fiber does not dissolve in water. Instead, it bulks up stool and aids in the movement of foods through the digestive tract. For those who experience occasional constipation, increasing your intake of insoluble fiber can be an effective treatment. [5]

How Much Fiber Do I Need?

So, now that you know what fiber actually is, you want to know how much of it you actually need to consume, right? According to the Institute of Medicine (IOM), adult men and women need 25 to 38 grams of dietary fiber a day from food, not supplements. [6] (Foods that are high in fiber have other nutrients and benefits, too, after all.) Unfortunately, most Americans are getting only 16 grams a day—about half the recommended amount. [7]

According to the United States Department of Agriculture (USDA), the government body responsible for establishing the nutritional guidelines and daily values you see on the nutrition labels of all your store-bought foods, recommends consuming 14 grams of fiber per 1,000 calories. At a 2,000-calorie reference level (which is appropriate for some but not all people), your recommended daily dietary fiber intake should be around 28 grams. [8]

How Much Fiber Is Too Much?

There is no tolerable upper intake level set for dietary fiber. This means that the amount of fiber that is "too much" can vary from person to person. Consuming large amounts of fiber at one time—especially if you are a low-fiber consumer!—may lead to temporary GI symptoms until your gut adapts, such as:

• Bloating
• Gas
• Abdominal cramps
• Constipation or diarrhea
• At very high levels of fiber consumption, fiber may interfere with the absorption of certain minerals such as iron, calcium, and zinc [9]

But keep in mind that the average American, as we mentioned, only gets around 16 grams of fiber per day. So, for most of us, the issue isn’t getting too much fiber but rather not enough. [7]

Tips for Increasing Fiber

It’s highly likely that you’re not eating enough fiber. In fact, national consumption surveys indicate that 95% of the U.S. population doesn't meet recommendations. Given that the average American consumes just 16 grams of fiber a day, it’s safe to say we’re well below expert recommendations. [7]

Good news though: There is a long list of high-fiber foods. So it’s not only easy to increase your daily intake, but it can also be delicious. Here’s your game plan:

1. Increase fiber slowly

Take it slow (remember?). There’s no reason to jump into things too quickly, and in fact, slowly increasing fiber amounts will help your body adjust. You’ve probably heard people complain about feeling bloated or getting cramps after eating too much fiber. You don’t have to be one of those people! Everyone reacts to fiber differently. What may be too much too fast for someone might be the right amount for you. Play it safe and introduce fiber-rich foods slowly.

Spreading out your fiber intake throughout the day can also help reduce the risk of bloating and gastrointestinal discomfort from excess fiber. For example, choose oatmeal for breakfast, add some beans to your salad at lunch, and snack on some nuts later that day. As the week goes on, you can start adding more fiber to each of your meals. So a few days later, dress up your oatmeal with some berries and seeds, add another fiber-rich vegetable to that salad, and so on.

2. Drink water

Another major factor in doing this right: Drink water and plenty of it. If you don’t hydrate enough while increasing fiber, you may experience occassional constipation—one of the very things that fiber can actually aid in fighting. Drink at least eight cups of water a day. (Pro tip: Keep a large water bottle at your side—on your desk, in the car, in the kitchen, or wherever you spend most of the day. It will remind you to drink, and you won’t have to stop what you’re doing to refill smaller glasses.)

3. Choose fiber-rich foods

Now for the fun part: adding delicious fiber-rich foods to your diet! Ideally, you’ll be swapping high-fiber foods (like the ones listed below) for low-fiber ones. For example, swapping white bread for whole grain. But when you're first starting, this might be hard to do. Instead, start by adding high-fiber foods to your diet in addition to what you’re already eating. Below, we list many great high-fiber sources to whet your appetite.

4. Set a fiber goal

Whatever pace you feel is right for your body, set a goal for yourself each day. It will help you hold yourself accountable. (And if you’re the competitive type, it helps to have a challenge to surmount.) For an easy way to get started, grab an OLIPOP!

High Fiber Foods

Ready to begin your high-fiber journey? Here are some of our favorite fibrous foods: [10]

Fruits:

• Raspberries
• Blackberries
• Pears
• Apples (with the skin)
• Avocado

Vegetables:

• Green peas
• Broccoli
• Brussel sprouts
• Collard greens

Grains, seeds, and nuts:

• Whole-wheat spaghetti
• Barley
• Bran flakes
• Quinoa
• Oatmeal
• Whole-grain bread
• Chia seeds

Legumes:

• Navy beans
• Split peas
• Lentils
• Chickpeas
• Black beans

Plant-based recipes are great for adding more fiber to your plate! If you’re hesitant to swap meat or chicken for high-fiber plant-based foods, remember that legumes like beans and lentils and even whole grains are also good sources of protein. 

If it’s the convenience of processed foods that feels difficult to give up, try tricks that make fruit and vegetables easier to reach for. Cut, wash, and peel food ahead of time, and try steaming vegetables for the fastest way to cook. The microwave works, too!

How Much Fiber Per Day: The Takeaway

The benefits of eating fiber far outweigh the hurdles to eating more. For most adults, the goal is between 25 to 38 grams of fiber per day. Choose foods you like, and take it slow. It won’t be long till you’re on your way to more fiber and better digestive health. You got this!

Sources

1. Harvard T.H. Chan School of Public Health. (2022, April). Fiber. The Nutrition Source. https://nutritionsource.hsph.harvard.edu/carbohydrates/fiber/
2. Goldman. (2016, May 16). Gut bust: Intestinal microbes in peril. Stanford Medicine Magazine. https://stanmed.stanford.edu/gut-bust/
3. Deehan, E. C., & Walter, J. (2016). The fiber gap and the disappearing gut microbiome: Implications for Human nutrition. Trends in Endocrinology and Metabolism, 27(5), 239–242. https://doi.org/10.1016/j.tem.2016.03.001
4. Soluble vs. insoluble fiber. (n.d.). Mount Sinai Health System. https://www.mountsinai.org/health-library/special-topic/soluble-vs-insoluble-fiber 
5. Dietary fiber: Essential for a healthy diet. (2022, November 4). Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983
6. Institute of Medicine. (2005). Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids. In National Academies Press eBooks. https://doi.org/10.17226/10490
7. Quagliani, D., & Felt-Gunderson, P. (2016). Closing America’s fiber intake gap. American Journal of Lifestyle Medicine, 11(1), 80–85. https://doi.org/10.1177/1559827615588079
8. United States Department of Agriculture. (2023, November 14). How much (dietary) fiber should I eat? AskUSDA. https://ask.usda.gov/s/article/How-much-dietary-fiber-should-I-eat
9. Ioniță-Mîndrican, C., Ziani, K., Mititelu, M., Oprea, E., Neacșu, S. M., Moroșan, E., Dumitrescu, D., Roșca, A. C., Drăgănescu, D., & Negrei, C. (2022). Therapeutic Benefits and Dietary Restrictions of fiber intake: A State of the art review. Nutrients, 14(13), 2641. https://doi.org/10.3390/nu14132641 
10. Chart of high-fiber foods. (2023, November 23). Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/high-fiber-foods/art-20050948 

Meet our Expert This article is reviewed by Dr. Renee Korczak Ph.D., RDN, CSSD, LD. Renee is an advanced practice registered dietitian nutritionist with expertise in digestive health. Renee has her board specialty in sports dietetics and continues to be active in the digestive health and sports nutrition space. Outside of work, Renee enjoys time with her two children and husband. She enjoys world travel, cooking, and yoga.