What Is Fiber and Why Do I Need It? A Dietitian Explains

Dive into the potential benefits, and side effects of fiber and learn how to incorporate more of this nutrient into your diet.

By Rachel Gargano, MS, RD, CSSD, CBS

— On Jul 20, 2025

What Is Fiber and Why Do I Need It? A Dietitian Explains

In this article:

Only about 5% of Americans get enough daily fiber in their diets. As a dietitian, I can’t help but be concerned about this statistic. Such a vital nutrient should be getting more love during meals and snack time, so I’m here to shed some light on fiber’s importance, how it works, and what to look for when you shop.

But before answering some of the most pressing questions, like what foods are high in fiber and how much dietary fiber do you need, we need to start with the basics: What is dietary fiber? Beginning with this foundation will help you better understand fiber’s benefits and why it’s crucial to get enough fiber to support digestion.

Did You Know? Live it Up Super Greens has 3 grams of dietary fiber from the natural superfoods and veggies in its formula.

What Is Dietary Fiber?

Dietary fiber is a type of carbohydrate, specifically a complex carb, that the body can’t digest or absorb. Whereas the body breaks down and absorbs the nutrients of other types of carbs, like sugars and starches, fiber passes through the digestive system largely intact.

Dietary fiber comes from the parts of plant cells that are not digestible by the human body. That’s because we don’t have the digestive enzymes to break down these quite complex carbs. This might sound like an evolutionary weakness, but fiber’s unique qualities make it a powerhouse for digestion and other bodily functions.

Soluble vs. Insoluble Fiber

The two main types of fiber are soluble and insoluble:

Soluble fiber dissolves in liquids, including water and other bodily fluids. As it dissolves, it creates a gel-like substance that helps to slow digestion.
Insoluble fiber does not dissolve in liquids, instead attracting and retaining water as it moves through the body. Because it’s not broken down by bacteria, this type of fiber stays mostly intact as it moves through the intestines (and eventually helps material move out of the body).

Prebiotic Fiber

Prebiotics are the food that bacteria feed off of in the gut. Not all soluble fibers are prebiotics, but most prebiotics are soluble. To be considered a prebiotic, the fiber has to stimulate the growth of certain bacteria, essentially acting as a fermentation station for good gut flora to thrive.

Universally recognized prebiotic fibers include fructooligosaccharides, inulin, and galactooligosaccharides, found in foods like lentils, chickpeas, barley grass, burdock root, artichokes, onions, garlic, and cow’s milk.

In terms of prebiotics vs. probiotics, prebiotics are the fuel for probiotics (the beneficial bacteria in the gut). Both are needed to support digestive functions.

How Much Fiber Per Day? Recommended Doses

The USDA’s Dietary Guidelines for Americans, 2020–2025, outlines the recommended daily fiber doses for adult men and women. Keep in mind that these are recommended amounts and may differ depending on an individual’s health needs.

Age	Women (fiber intake goal)	Men (fiber intake goal)
19–30 years old	28g	34g
31–50 years old	25g	31g
Over 50 years old	22g	28g

More than 90% of men and women in America don’t consume enough fiber, eating only about 10-15 grams of fiber per day, a staggering statistic considering how important this nutrient is to health (more on health benefits next).

What Are the Health Benefits of Fiber?

Fiber is a powerhouse nutrient that’s crucial to supporting certain functions of the body. Here are three key areas where fiber can benefit your health.

1. Digestion

One of the main benefits of fiber is digestion support. While much of the digestive work is behind the scenes, there is one very noticeable indicator of digestive function: bowel movements.

Both soluble and insoluble fiber help to regulate the digestive system in different ways. Soluble fiber takes on water and other liquids as it moves through the gastrointestinal tract, and as it absorbs liquids, a gel-like substance is produced that softens stool, potentially increasing the frequency of bowel movements and helping with constipation because stools are easier to pass.

Foods containing soluble fiber include:

Fruits like apples, oranges, pears, cherries and strawberries
Flaxseeds and chia seeds
Vegetables like onions, artichokes, and potatoes
Oats, whole grains, and barley

Insoluble fiber is the bulking component for stool because it does not absorb liquids, remaining largely unchanged as it travels through the digestive system. This can be particularly helpful for individuals experiencing loose stools.

Foods containing insoluble fiber include:

Citrus fruits
Legumes
Vegetables like cabbage and peas
Pasta, bran, whole grains, and oats

Did You Know? Many foods contain both soluble and insoluble fiber. An apple is a great example, as the flesh contains soluble fiber, and the skin has insoluble fiber.

2. Gut Microbiome Support

The gut microbiome is an extremely active place, full of microorganisms like bacteria that work hard to assist with multiple functions in the body, such as digestion, immunity, the nervous system, and the endocrine system. When you hear the phrase “gut microbiome support,” that means that a nutrient helps to ensure that the environment in your small and large intestine stays healthy and thriving to keep these bodily functions in great shape.

Prebiotic fiber is one of those nutrients that lends a helping hand to the gut. It does so by providing food that helps the beneficial gut bacteria grow, leaving less space in the digestive tract for potentially harmful bacteria, like E. coli or Salmonella. When bacteria feed on the prebiotics, this produces short-chain fatty acids, which have been shown to regulate inflammation.

A healthy diet needs adequate fiber. Without enough, like soluble vs. insoluble fiber, as well as probiotics, the gut microbiome can become off balance, potentially letting pathogenic bacteria outgrow the “good” gut bacteria. This may lead to digestive, inflammatory, and even immune issues.

3. Weight Management

Soluble fiber, specifically, can help with weight control, as the gel-like substance that is produced typically slows digestion—and slower digestion means that individuals may feel full for longer and therefore consume fewer calories.

Studies also show that one of the short-chain fatty acids produced during fermentation, acetate, has been shown to induce appetite-suppression neuroactivity in the brain.

While these benefits of fiber are clear through studies, actual results may depend on a person’s unique physical makeup, diet, activity level, medical conditions, and other factors. I always recommend clients focused on weight loss should prioritize exercise and a healthy diet full of whole fruits and vegetables.

What Are the Best High-Fiber Foods?

For a high-fiber diet, look out for the following fiber-rich foods as you walk down the grocery aisles or peruse a restaurant menu. Additionally, many supplements, like greens powders, contain some of these foods.

Did You Know? While many processed foods contain fiber, the nutrient may only be included in small amounts, as processing or refining often strips the fiber-rich components of a particular ingredient. For example, white flour doesn’t contain as much fiber as whole-wheat flour because the bran and germ of the wheat kernel are removed during the refining process.

This list is organized by category and then by how much fiber the food contains (from highest to lowest). Total grams of fiber are per 1/2 cup unless specified otherwise.g

Fruits

Whole apple (with skin): 4.8g
Guava: 4.5g
Raspberries: 4g
Blackberries: 3.8g
Kiwi fruit: 2.7g
Dried figs: 1.9g
Strawberries: 1.5g

Vegetables

Green beans (cooked): 4.4g
Canned pumpkin: 3.6g
Brussels sprouts (cooked): 3.2g
Broccoli (cooked): 2.6g
Cauliflower (cooked): 2.5g
Spinach (cooked): 2.2g
Carrots (raw): 1.8g

Legumes

Small white beans (cooked): 9.3g
Lentils (cooked): 7.8g
Pinto beans (cooked): 7.7g
Chickpeas (cooked): 6.3g
Green peas (cooked): 4.4g
Edamame (cooked): 4.1g

Whole Grains

Wheat bran cereal: 14g
Popcorn: 5.8
Bulgar (cooked): 4.1g
Cooked oats: 4g
Whole-wheat crackers (1 ounce): 2.9g
Whole-wheat bread (1 slice): 1.9g

Dietitian Tip: Even though products that say “whole grains” likely have fiber, the amount isn’t the same across the board. Fiber amounts vary by the type of whole grain, so make sure to take a closer look at the nutrition label.

Nuts and Seeds

Pumpkin seeds (1 ounce): 5.2g
Chia seeds (1 ounce): 4.1g
Almonds (1 ounce): 3.5g
Pine nuts (1 ounce): 3g
Pistachios (1 ounce): 2.9g

Can You Eat Too Much Fiber? Side Effects

With fiber, can there be too much of a good thing? Yes, some side effects may occur with significant and sudden increases in dietary fiber intake and ingesting too much fiber. The following are potential issues that may occur with a higher fiber intake:

Bloating and gas: The byproduct of fiber fermentation in the gut is, unfortunately, gas. Some people may experience flatulence and bloating when eating foods high in fiber, especially if they suddenly increase their intake of dietary fiber. But these side effects may decrease over time; several studies show that the level of flatulence from increased intake of peas, beans, chickpeas, and lentils decline as the weeks go by.
Abdominal cramping: Some people may feel pain and cramping in their abdomen due to fiber either being fermented or physically rubbing up against the inside of the intestines.
Constipation: Ingesting insoluble fiber without adequate water intake can harden stools and lead to constipation.
Diarrhea: Individuals with bowel conditions may experience diarrhea if they have too much fiber.
Dehydration: Fiber absorbs water in the intestines, so that water needs to be replenished. Ingesting fiber without getting enough fluids can dehydrate the body.
Intestinal blockage: Rare but serious, an intestinal blockage or impaction may occur with extremely high dietary fiber intake and low hydration or in individuals with narrowed intestines. Seek medical attention immediately if you experience severe abdominal cramping and swelling, vomiting, constipation, and gas, as these may be symptoms of an intestinal blockage.

Dietitian Tips for Increasing Intake of Dietary Fiber

Although most Americans aren’t getting enough fiber, it’s important to speak with your doctor or a registered dietitian before adding more high-fiber foods to your diet. That said, if you want a higher fiber intake, here are some tips:

Eat a diverse selection of high-fiber foods (reference the helpful list earlier in this article for ideas). Remember that it’s important to have a mix of foods with soluble vs. insoluble fiber.
To prevent digestive discomfort, start small with a high-fiber diet, gradually incorporating more fiber-rich foods.
Make easy switches, like baking with whole-wheat flour instead of white flour, eating brown rice instead of white rice, or blending spinach into smoothies (you likely won’t even taste it!).
Choose grocery items that list higher amounts of fiber on the nutrition label.
Drink enough water to aid fiber’s effectiveness and prevent certain side effects, like dehydration and constipation.
Consider incorporating greens powders into your diet as an easy addition to smoothies or meals. These supplements often contain fiber from whole vegetables and fruits. Be sure to check the amount of fiber per serving to ensure that you’re getting the right amount of the nutrient each day.

How Live it Up Can Help Meet Your Fiber Needs

Live it Up Super Greens Package as Featured on Forbes 2025

Getting the right amount of fiber for your body can be overwhelming, especially for on-the-go individuals. While certain food switches are easier than others, some people find that they just can’t prepare enough whole-food snacks and meals to up their fiber intake.

That’s where greens supplements like Live it Up Super Greens can help. Super Greens is an all-natural greens powder for daily health, supporting digestion, immunity, and energy. Through a diverse mix of vegetables and superfoods, Super Greens helps fill gaps in your diet and offers a balanced amount of fiber (3g total) from whole-plant foods (compared to supplemental fiber added to AG1’s ingredient list).

As I’ve shared, dietary fiber is beneficial for digestion and a thriving gut microbiome, but significant benefits may only be seen with an array of fiber types: soluble, insoluble, and prebiotics. Live it Up Super Greens includes:

Fiber-rich foods like spinach, alfalfa leaf, and barley grass leaf
Foods with prebiotics, like burdock root and broccoli
5 billion CFUs of live probiotic strains that can feed on prebiotics and contribute to gut health

Live it Up Super Greens is a great way to supplement your diet with a bit more fiber and lots of gut-friendly ingredients (plus, customers say it tastes great!).

Dietitian Tip: Assessing your current fiber intake will help you understand how much more fiber you need through other whole foods to reach your recommended daily dose. Additionally, consult a healthcare professional before making any significant changes to your diet, as everyone’s health needs are unique.

Frequently Asked Questions About Fiber

Do you still have burning questions about fiber? Learn more about this nutrient through the following commonly asked questions.

Why is fiber important?

Fiber is important for several reasons, one of the most important being digestive health. It feeds the “good” bacteria in the gut, serving as a prebiotic. This not only leaves less room for bad gut bacteria to grow but also produces acids that support colon health. Fiber has been shown to slow digestion, relieve constipation, and assist gut inflammation.

Does fiber make you poop?

Fiber can make it easier to poop, either by making stools softer (and therefore easier to pass) or making stools more firm (helping with loose stools or diarrhea).

It’s important to have a high-fiber diet full of the recommended amount and sources of fiber (insoluble and soluble fiber). But if you’re struggling with ongoing diarrhea or constipation, talk with a healthcare provider before increasing or decreasing your fiber intake.

Does fiber make you gassy and bloated?

Yes, fiber can make you gassy and bloated because the byproduct of gut bacteria feeding on soluble fiber is gas. Think of it like fermentation, whereas insoluble fiber is a “nonfermentable” fiber that passes through the intestines without the gaseous byproduct. People who have recently increased their intake of high-fiber foods may notice more gas and bloating.

Does fiber cancel out carbs?

Fiber does not cancel out carbs. In fact, fiber is a type of carbohydrate—it just isn’t processed by the body the way that other carbs are.

People on carb- or sugar-restricted diets often subtract fiber and sugar alcohols from the total carbs to reach what’s called “net carbs.” With this practice, fiber doesn’t cancel out carbs; rather, it’s deducted from the total amount. It’s important to note that counting net carbs can be unreliable and isn’t approved by government health agencies or the American Diabetes Association. Be sure to talk with your healthcare provider to ensure that you’re ingesting the right amount of carbohydrates for your body.

How long does it take for fiber to work?

The length of time it takes for fiber to work depends on the outcome you’re hoping for. For slowed digestion, you may feel full immediately or in a few hours. Changes in bowel movements may be noticed in anywhere from one to three days. For any other health benefits from fiber, talk with your healthcare provider about when to test for certain health markers.

What happens when you lack fiber?

A lack of fiber may result in some unwanted side effects, like increased gut inflammation and reduced immune responses due to an increase in pathogenic bacteria in the gut, diarrhea, constipation, irregular bowel movements, and potentially more difficulty with weight management.

What is the best fiber supplement?

Taking fiber supplements may increase individuals’ fiber intake and positively impact their digestive health. But some of the best supplements don’t only target fiber—they provide comprehensive, balanced nutrition. Live it Up Super Greens is one of these supplements, providing dietary fiber, prebiotics, probiotics, digestive enzymes, and many other health benefits through all-natural, organic fruits and vegetables.

References

About the author:

Rachel Gargano, MS, RD, CSSD, CBS

Rachel is a registered dietitian based in Contra Costa County, California, with over 15 years experience. She specializes in whole-body wellness and plant-based nutrition, helping people understand the dynamic interplay between food and health so they can live life to the fullest. When not helping others, she enjoys spending time with her kids, being physically active, and tending to her abundant household plants.

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