Not all fiber is equal; Doctors share which types really promote longevity.

Fiber is known to be a crucial part of a healthy diet as it promotes satiety and gut health.

As trends like “fibermaxxing” make high-fiber consumption more popular, understanding the best sources is increasingly important for individual health, according to nutritionists.

Longevity expert Peter Attia, a Stanford University physician based in Austin, Texas, discussed how fiber aligns with a healthier lifestyle in a preview of his latest “Ask Me Anything” episode of “The Peter Attia Drive” podcast.

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People who adopt a beneficial habit, such as eating a high-fiber diet, tend to do “many other healthy things,” according to the doctor.

“They may be exercising more. They’re much less likely to smoke. They’re probably sleeping more,” he said. “You’re very likely capturing other healthy habits when you try to simply measure one thing.”

For this reason, it can be difficult to “unravel” the specific effects of fiber, Attia said, since people who eat more fiber also tend to consume other beneficial plant nutrients and generally choose healthier lifestyles.

Different types of fiber

According to Attia, different types of fiber are known to work differently in the body.

“There are many things that are classified as fiber, [and] a wide range of physical properties that a particular fiber might have, but these different properties produce different effects on the body,” he said.

“Some fibers primarily provide microbiome support because they are actually fermented by gut microbiomes. Some fibers may improve blood sugar…and others simply increase stool bulk.”

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Soluble fiber dissolves in water, while insoluble fiber does not, and each type plays a different role in digestion.

Insoluble fiber includes vegetables, fruit skins, whole grains and bran, according to Attia. It will remain “virtually intact” as it moves through the digestive system, adding bulk to stool, reducing constipation, and supporting regular bowel movements.

Insoluble fibers are not fermented by intestinal bacteria, but they stimulate the lining of the intestine to release water and mucus, which “dilutes toxins in the colon” and speeds up “intestinal transit,” the doctor said.

More soluble or viscous fiber can absorb water and create a gel in the intestine that can cause slower gastric emptying, reduce blood sugar spikes and potentially lower cholesterol levels, according to Attia.

Some examples of soluble fiber include pectin (found in fruits), beta-glucan (found in whole oats), and psyllium husk, which is a plant most commonly consumed as a supplement.

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Some soluble fibers belong to a subgroup called fermentable or prebiotic fibers. These fibers are broken down by intestinal bacteria to produce short-chain fatty acids (SCFAs), compounds like butyrate that help maintain intestinal health, regulate pH, improve metabolism and reduce inflammation, according to several studies.

“My mantra is ‘baby steps’ every time I introduce fiber… Little by little goes a long way.”

Fermentable fibers are found in foods such as beans, pectin, and inulin, as well as prebiotic sources such as onion, garlic, asparagus, and chicory root. They are also present in certain resistant starches, including green bananas, legumes, and starchy cooked foods such as potatoes, rice, and pasta.

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Resistant starches, although fermentable, are not soluble, Attia noted. They are classified into several types:

• RS1: Found in whole grains, seeds and legumes.
• RS2: Found in raw potato starch, green bananas, and corn starch (commonly used in fiber supplements).

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Most diets consume a combination of fiber types. Plant-based foods, especially those with skin, along with oats, beans and legumes, tend to be the richest sources, Attia shared.

Benefits of diets rich in fiber

Some key benefits of a high-fiber diet include satiety and weight management, glycemic control, cardiovascular health and colorectal cancer prevention, Attia said.

Robin DeCicco, a certified holistic nutritionist in New York, shared with News Digital in a previous interview that increasing your fiber intake can be “quite beneficial.”

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“Everything from gastrointestinal health to cardiovascular health, weight management, prevention of diabetes and certain cancers, to feeling fuller throughout the day and minimizing cravings for sugars and starches are all major benefits of fiber intake,” she said.

Because health is individualized, DeCicco cautioned that those with preexisting gastrointestinal conditions could experience complications from introducing too much fiber at once.

“If your system is not used to fiber and starts to become overloaded, you can easily become bloated, crampy and constipated,” he said.

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According to DeCicco, it’s “easier on the stomach” to distribute, since the fiber can build up in the stomach and cause a flashback.

“That’s why it’s especially important to incorporate fiber slowly,” she said. “My mantra is ‘baby steps’ whenever I introduce fiber to any client. Little by little goes a long way toward long-term health.”