It’s a scientific oddity: an essential nutrient for whole-body health is a substance your body can’t even digest. And yet studies show that most Americans need more of it. Dietary fiber is one of the most misunderstood but vital components of your diet: it’s an aid to digestion, heart health, and weight loss—precisely because your body can’t use it.

The confusion is understandable. However, this guide should clear up any questions about the benefits of dietary fiber and highlight where to get more of this essential nutrient.

What exactly is fiber?

So named for the fibrous texture in foods that provide this nutrient, dietary fiber is a carbohydrate our bodies can’t process. With most simple carbohydrates, such as bleached flour, your body breaks them down into sugars. These sugars supply glucose to power your brain and energize the cells that make your body function. In excess, sugars can turn into fatty tissue and lead to health consequences like tooth decay, diabetes, and heart disease.

However, fiber molecules are special. Even though they are carbohydrates, your digestive system can’t break them down into sugars. Instead, the body passes them through the intestinal tract mostly unchanged. But while eating an indigestible substance would normally be bad for you, fiber actually cleanses the body while journeying through it. The health benefits vary based on which type you consume.

Soluble vs. insoluble fiber

There is common confusion about the terms soluble fiber and insoluble fiber. Both are indigestible; what differentiates them is whether or not they dissolve in water.

When you consume soluble fiber from grains like oatmeal or fruits such as apples, it turns into a gel-like substance in the body. Now imagine this gel mixing with other food in your stomach. Because of its sticky properties, it slows the digestive process. This is a good thing, even though it may not seem to be.

By slowing digestion, soluble fiber makes you feel full faster and suppresses your appetite longer, reducing calorie consumption and even preventing weight gain. It also slows the absorption of sugars into the bloodstream, alleviating spikes in blood glucose levels, and can even help lower blood cholesterol to promote a healthy cardiovascular system.

In contrast, when you get insoluble fiber from sources like whole grains and green, leafy vegetables, it remains mostly solid. Because it’s insoluble, this type of fiber attracts water as it courses through your intestinal tract, helping to keep you regular. On a macro scale, a meta-analysis reported by the National Library of Medicine concluded that fiber may actually reduce your risk of colorectal cancer.

This just scratches the surface of fiber’s many health benefits. As the Harvard T.H. Chan School of Public Health states, “Fiber appears to lower the risk of developing various conditions, including heart disease, diabetes, diverticular disease, and constipation. Fiber’s beneficial role in the gut microbiome . . . [may] alleviate the chronic inflammation associated with these conditions.”

Getting your fiber

It’s crucial to consider both soluble and insoluble fiber when making dietary choices. The average adult needs at least 25 grams of fiber a day, depending on age, sex, and other factors. However, most Americans only get about 15 grams. There are several reasons why this may be the case, including diets high in processed, simple carbohydrates and meat, which rarely offer fiber at all.

Despite this widespread deficiency, fiber is an extremely common nutrient. There’s little need to turn to supplements when you can add very accessible, high-fiber foods to your diet. The following are all excellent sources of soluble and/or insoluble fiber:

• Apples
• Beans and lentils
• Blueberries and other berries
• Brown rice
• Citrus fruits
• Fruits often confused for vegetables, like cucumbers and tomatoes
• Leafy vegetables like kale and spinach
• Nuts
• Root vegetables like carrots and potatoes
• Seeds
• Whole-wheat flour

This is just an abbreviated list; there are many other fiber-packed foods out there. In fact, you can safely assume that increasing your intake of many natural grains, fruits, and vegetables will boost your dietary fiber.

Final fiber thoughts

You may feel digestive discomfort, including pain and bloating, upon suddenly increasing your fiber intake. However, once you find a healthy balance in your diet, these symptoms should fade. Try to avoid getting this nutrient from supplements unless your doctor specifically recommends them since they are more likely to cause side effects.

Also, forgo processed foods like prepackaged meals and breakfast cereals, many of which are stripped of fiber during production. Some processed foods claim to be good sources of this nutrient, but oftentimes they only offer a few grams per serving. For an overall healthier diet, eat more whole foods. If you base your diet on fruits, vegetables, whole grains, and other fiber-packed foods, dietary fiber is just one of the many benefits to be found.

Finally, keep in mind that because you get calories and digestive bulk from fiber-rich meals, you’re likely to feel full before consuming excess levels. In fact, more Americans should be concerned about consuming too little fiber, not too much. Its many potential benefits, such as improved heart health and cancer prevention, are significant and make the nutrient a necessity for maximizing your health.

Be sure to discuss your fiber intake with your doctor.