Fiber is a type of carbohydrate that the body can’t digest. It's found in plant foods like fruits, vegetables, whole grains and legumes. Fiber comes in two main forms: soluble and insoluble, each offering unique health benefits. 

Soluble Fiber:

• Dissolves in water.
• Forms a gel-like substance in the digestive tract.
• May help lower cholesterol and improve blood sugar control.
• Sources include oats, barley, fruits and legumes. 

Insoluble Fiber:

• Does not dissolve in water.
• Adds bulk to stool, which can help with constipation.
• Sources include wheat bran, whole grains and the skins of some fruits. 

“It’s important to understand that while fiber is not something that humans can digest, we do harbor a gut microbiome that digest fiber for us,” explains gastroenterologist Peter Mannon, MD. 

Dr. Mannon went on to say that prebiotics—which can include fiber, resistant starches, fructans and polyphenols—are compounds used by gut bacteria. Prebiotics are not digestible by humans, but they affect the gut bacteria in a beneficial way. 

Many fruits, vegetables and grains are good sources of prebiotics, which are types of fiber that feed beneficial gut bacteria. Some excellent prebiotic foods include: 

• Leeks 

• Asparagus

• Apples 

• Oats 

• Barley

• Soybeans 

• Chicory root

• Flaxseeds

How much fiber do I need in my diet?

According to Dr. Mannon, the average person should aim for at least 25 grams of fiber per day. When looking for fiber rich foods, avoid highly processed foods, or foods with added sugar. The best foods for gut health are rich in fiber compared to their weight. 

“Concentrate on eating seeds, nuts, root vegetables, whole grains and beans,” says Dr. Mannon. “These groups tend to give you more fiber per ounce. Compare this to vegetables like lettuces or tomatoes which contain more water that fiber.”

When increasing the fiber in your diet, don’t try to double your fiber intake overnight. Instead, gradually increase it over 3-4 weeks so your gut has time to adjust. This helps minimize bloating or gas. 

Also, aim for fiber variety—don’t rely on the same source or a daily supplement.  Otherwise, you’ll miss an opportunity to promote all the healthy bacteria that benefit digestion. In fact, diversity in your gut microbiome is a keystone of good health.

How do I know if I’m getting enough fiber?

“One of the easiest to recognize signs that you’re not getting enough fiber is constipation,” says Dr. Mannon. “A low-fiber diet can also leave you susceptible to systemic inflammation.” 

Systemic inflammation has been linked to heart disease, obesity and metabolic syndrome. Studies have shown that a fiber-rich, prebiotic diet can help reduce this risk, making high-fiber foods an important part of an anti-inflammatory eating plan.

How do I increase my daily fiber intake?

“A good place to start when looking for high-fiber foods is on trusted website, such as a professional society of nutritionists or academic medical website,” says Dr. Mannon. “Use these resources to learn about the fiber content of foods versus their calorie content. For example, nuts are a good source of fiber and selenium, a trace mineral your body needs. But, nuts are also high in calories, so you’ll want to keep track of your portion size.”

When you’re aiming to add fiber from a variety of sources, start with meals that are easy to prepare. For example, you can make overnight oats by simply mixing oatmeal with milk (according to package directions) and refrigerating overnight. Add in a tablespoon of chia seeds to get up to 8 grams of additional fiber. In the morning, you can top it off with berries or sunflower seeds for even more fiber. 

When increasing your fiber intake, Dr. Mannon recommends a gradual approach. “If your goal is to reach 25 grams of fiber per day and you’re currently getting eight grams, increase your fiber intake by four grams per week over four weeks,” he explains. “For example, on week one, set a goal of 12 grams of fiber per day. The next week, increase your fiber to 16 grams, and so on until you hit your goal.”