What do the two types of fiber do?

November 22, 2025 •

2 min read

According to the Harvard T.H. Chan School of Public Health, most Americans consume only about half of the recommended daily fiber intake, which is typically 25 to 35 grams. Understanding what do the two types of fiber do is crucial for bridging this nutritional gap and optimizing your health, as they each play different yet vital roles in the body.

Quick Summary

This article explains the roles of soluble and insoluble fiber. Soluble fiber dissolves in water, forming a gel that aids in lowering cholesterol and stabilizing blood sugar. Insoluble fiber adds bulk to stool, promoting regular bowel movements and preventing constipation.

Key Points

Soluble vs. Insoluble Fiber: Soluble fiber dissolves to form a gel, while insoluble fiber adds bulk to stool.
Heart Health: Soluble fiber is particularly effective at lowering LDL ('bad') cholesterol, reducing the risk of heart disease.
Blood Sugar Control: Soluble fiber slows digestion, which helps prevent sudden spikes in blood sugar levels.
Digestive Regularity: Insoluble fiber is crucial for promoting regular bowel movements and preventing constipation.
Gut Health: Soluble fiber acts as a prebiotic, feeding beneficial bacteria in your colon to support a healthy gut microbiome.
Fullness and Weight Management: Both types of fiber, especially soluble fiber, help you feel full longer, which can assist with weight control.
Varied Diet: Eating a mix of high-fiber plant-based foods ensures you receive the benefits of both types of fiber.

Soluble Fiber: The Dissolving Gel

Soluble fiber dissolves in water to form a gel in the digestive tract, impacting heart health, blood sugar control, and satiety. This gel slows digestion and nutrient absorption.

Functions and Health Benefits of Soluble Fiber

Soluble fiber helps lower LDL cholesterol by binding to bile acids, prompting the body to use stored cholesterol. It also stabilizes blood sugar by slowing digestion and feeds beneficial gut bacteria, producing short-chain fatty acids that reduce inflammation. The gel also increases fullness, aiding weight management.

Food Sources for Soluble Fiber

Sources include legumes, oats, barley, apples, citrus fruits, berries, carrots, brussels sprouts, broccoli, flax seeds, and chia seeds.

Insoluble Fiber: The Bulking Agent

Insoluble fiber does not dissolve in water, acting as roughage that adds bulk to stool. This is crucial for regulating bowel movements.

Functions and Health Benefits of Insoluble Fiber

By adding bulk and attracting water, insoluble fiber softens stool and speeds waste movement, preventing constipation. It also supports bowel health by reducing the risk of hemorrhoids and diverticular disease and aids digestive function by keeping intestinal muscles active.

Food Sources for Insoluble Fiber

Sources include whole grains, wheat bran, brown rice, leafy greens, cauliflower, green beans, potatoes with skin, almonds, walnuts, and fruit skins.

Comparison of Soluble vs. Insoluble Fiber

Both fiber types are found in most high-fiber plant foods but have different actions.


Feature	Soluble Fiber	Insoluble Fiber
Dissolves in Water?	Yes, forms a gel	No, passes through intact
Effect on Digestion	Slows down digestion	Speeds up digestive transit
Primary Function	Lowers cholesterol and blood sugar	Adds bulk to stool
Main Benefits	Heart health, blood glucose control, satiety	Regular bowel movements, constipation relief
Key Food Sources	Oats, beans, apples, carrots	Wheat bran, nuts, green beans, potato skins

Conclusion: A Balanced Approach to Fiber

Both soluble and insoluble fiber are vital for a healthy diet, offering unique benefits for managing blood sugar, cholesterol, and digestive regularity. The best approach is to consume a variety of plant-based foods for a healthy mix. Gradual increase and plenty of water help prevent side effects. A diverse diet supports heart health and a healthy gut microbiome.

Get More Fiber Into Your Diet

Here are some practical ways to boost your daily fiber intake:

Start with high-fiber breakfast cereals like oatmeal with berries and chia seeds.
Choose whole grains over refined grains.
Add legumes to meals.
Snack on whole fruits and raw vegetables.
Add seeds like flaxseed to smoothies or yogurt.

Frequently Asked Questions

The main difference is their interaction with water. Soluble fiber dissolves in water and forms a gel-like substance, whereas insoluble fiber does not dissolve and passes through the digestive system mostly intact.

Soluble fiber is most effective for lowering cholesterol. It binds to bile acids in the small intestine, which forces your body to use stored cholesterol to produce more, ultimately reducing blood cholesterol levels.

Insoluble fiber is primarily known for helping with constipation. It adds bulk to your stool and attracts water, which helps it move more quickly and easily through the digestive tract.

Yes, for optimal health, it is important to consume both. A balanced diet containing a variety of fruits, vegetables, legumes, and whole grains ensures you get the unique benefits of both soluble and insoluble fiber.

Foods rich in soluble fiber include oats, barley, nuts, seeds, beans, lentils, peas, and many fruits and vegetables, such as apples, carrots, and brussels sprouts.

Common sources of insoluble fiber are whole grains, wheat bran, whole-wheat flour, nuts, beans, and vegetables like green beans, cauliflower, and potatoes with the skin.

While fiber supplements can be an option, especially if recommended by a healthcare professional, whole foods are generally better. They provide a wider variety of fiber types, vitamins, and minerals that supplements often lack.