What Are the Three Main Types of Fiber?

January 1, 2026 •

3 min read

According to the U.S. Dietary Guidelines, most Americans consume only about half of their recommended daily fiber intake. When focusing on how to increase consumption, it is important to understand what are the three main types of fiber: soluble fiber, insoluble fiber, and resistant starch. Each type has unique characteristics and benefits that contribute to overall digestive health.

Quick Summary

This guide explains the three primary types of dietary fiber: soluble, insoluble, and resistant starch. Learn how each functions in the body, its unique health benefits, and where to find it in common foods.

Key Points

Three Main Types: The three main types of fiber are soluble, insoluble, and resistant starch, each with unique properties and health benefits.
Soluble Fiber Benefits: It dissolves in water to form a gel, which helps lower LDL cholesterol and stabilizes blood sugar levels.
Insoluble Fiber Benefits: It adds bulk to stool and promotes regular bowel movements, preventing constipation and related issues.
Resistant Starch Benefits: It is a prebiotic fiber that feeds beneficial gut bacteria, producing short-chain fatty acids that improve gut health.
Sources Matter: You can find soluble fiber in oats and beans, insoluble fiber in whole grains and vegetable skins, and resistant starch in legumes and cooked/cooled starches.
Increase Gradually: Increase your fiber intake slowly and drink plenty of water to avoid gas, bloating, and cramping.

Understanding the Three Main Types of Fiber

Dietary fiber, the indigestible part of plant foods, is not a single substance but a complex group of carbohydrates that plays a critical role in human health. Rather than simply passing through the body, different types of fiber interact with the digestive system in unique ways to promote regularity, support gut health, and lower the risk of chronic disease. The three primary categories—soluble fiber, insoluble fiber, and resistant starch—offer distinct advantages when incorporated into a balanced diet.

Soluble Fiber

Soluble fiber dissolves in water, forming a gel in the gut that slows digestion. This helps stabilize blood sugar, promotes fullness, and can lower LDL cholesterol by binding to fatty acids.

Common sources of soluble fiber include:

Oats and oat bran
Beans, peas, and lentils
Apples, citrus fruits, and carrots
Barley
Psyllium

Insoluble Fiber

Insoluble fiber does not dissolve in water but adds bulk to stool by absorbing fluid. This promotes regular bowel movements, prevents constipation, and can reduce the risk of hemorrhoids and diverticular disease.

Common sources of insoluble fiber include:

Whole-wheat flour and wheat bran
Nuts and seeds
Green beans and leafy greens
Skins of fruits and vegetables
Brown rice and quinoa

Resistant Starch

Resistant starch resists digestion in the small intestine and is fermented by gut bacteria in the large intestine. This process produces short-chain fatty acids (SCFAs) that nourish colon cells, reduce inflammation, improve gut health, and can help regulate blood sugar and insulin sensitivity.

Foods high in resistant starch include:

Green (unripe) bananas
Cooked and cooled starches (potatoes, pasta, rice)
Legumes and beans
Oats and barley

Comparison of Fiber Types


Feature	Soluble Fiber	Insoluble Fiber	Resistant Starch
Dissolves in Water?	Yes	No	Varies (often similar to soluble)
Digestive Action	Forms a gel; slows digestion	Adds bulk; speeds up transit time	Resists digestion; ferments in large intestine
Primary Benefit	Lowering cholesterol, stabilizing blood sugar	Preventing constipation, promoting regularity	Feeding beneficial gut bacteria (prebiotic effect)
Texture in Food	Soft, moist	Rough, gritty	Varies (e.g., firm in cooked and cooled potatoes)
Sources	Oats, beans, apples, carrots	Whole grains, nuts, vegetable skins	Unripe bananas, cooked/cooled potatoes

How to Increase Your Fiber Intake Safely

Gradually increase your fiber intake over several weeks to avoid digestive discomfort like bloating and gas. It's also crucial to drink plenty of fluids, especially water, as fiber needs hydration to move through your digestive system. Prioritize obtaining fiber from whole foods, which offer a wider array of nutrients compared to supplements.

Conclusion: A Diverse Approach to Fiber

Consuming a variety of the three main types of fiber—soluble, insoluble, and resistant starch—is key to comprehensive digestive health and overall well-being. Soluble fiber aids in blood sugar and cholesterol control, insoluble fiber ensures digestive regularity, and resistant starch supports a healthy gut microbiome as a prebiotic. By including a wide range of plant-based foods such as fruits, vegetables, whole grains, and legumes in your diet, you can benefit from the unique properties of each fiber type and promote a healthier lifestyle. For further information on dietary fiber, the Harvard T.H. Chan School of Public Health is an excellent resource.

Tips for Incorporating More Fiber

Start your day with high-fiber breakfast foods like oatmeal or whole-grain cereal.
Choose whole grains over refined grains.
Add legumes to meals.
Snack on raw vegetables, nuts, or seeds.
Eat whole fruits instead of juice.

Health Benefits of Each Fiber Type in Detail

Each fiber type offers specific health advantages. Soluble fiber's gel nature helps lower LDL cholesterol and stabilizes blood glucose. Insoluble fiber prevents constipation and may reduce the risk of diverticular disease by adding bulk and promoting bowel regularity. Resistant starch, a prebiotic, nourishes gut bacteria, producing beneficial SCFAs like butyrate which support colon cell health and reduce inflammation. The specific benefits can vary slightly depending on the source of resistant starch. A varied diet ensures you gain the full spectrum of fiber's benefits for your digestive system and beyond.

Incorporating Variety for Optimal Health

To ensure you get a good mix of fiber types, focus on dietary variety. Combine different fiber sources throughout your day, such as oatmeal with berries (soluble, insoluble, resistant starch) for breakfast, a salad with greens, seeds, and chickpeas (soluble, insoluble, resistant starch) for lunch, and a dinner featuring brown rice, lentils, and green beans (all three types). This diverse approach maximizes the health advantages from all three fiber categories.

Frequently Asked Questions

Soluble fiber dissolves in water and forms a gel, helping to lower cholesterol and control blood sugar. Insoluble fiber does not dissolve in water; it adds bulk to stool and promotes regularity.

Good sources of soluble fiber include oats, beans, peas, lentils, apples, carrots, and citrus fruits.

Insoluble fiber is found in foods like whole-wheat products, nuts, leafy greens, and the skins of many fruits and vegetables.

Resistant starch is a type of fiber that resists digestion in the small intestine. It is important because it is fermented by beneficial gut bacteria, which produces health-promoting compounds like short-chain fatty acids.

Resistant starch is found in unripe bananas, cooked and cooled potatoes or rice, legumes, and beans.

It is generally better to get fiber from whole foods, as they provide a wider variety of fiber types, vitamins, and minerals that supplements lack.

While difficult to achieve, consuming too much fiber, especially too quickly, can cause gas, bloating, and cramping. It is best to increase your intake gradually and drink plenty of water.