It’s easy to get caught up in novelty and radical changes when it comes to eating better: Maybe the secret to a better diet is eating like a caveman, or only eating meat, or radically altering when you eat, right?

Hearing that you should eat more fiber, on the other hand, feels kind of stale, like something off of a poster from high school health class. Aren’t we past that? But that’s perhaps because we’ve paused stock of the full effect fiber can have. Nutritionists almost sound like they're shilling diet pills when they simply spell out the stuff it’s clinically proven to do: Not only does it lower cholesterol and inflammation in the body; it also helps regulate our levels of blood sugar by slowing glucose absorption. Taken together, those three effects have a huge impact on the development of chronic diseases later in life: heart disease, diabetes, all kinds of respiratory diseases.

It’s not like fiber is hard to get into your diet. It’s a catchall term for the indigestible parts of plant-based foods, so fruits, beans, vegetables, and whole grains are all excellent sources. But on average, Americans get about 16 grams of fiber per day—less than half of the amount we should be eating.

What Science Says

A commission set up by the World Health Organization sought to quantify exactly how much fiber people should eat by analyzing 40 years’ worth of data: 185 observational studies, as well as 58 clinical trials cumulatively involving close to 5,000 adults. Their results were published by The Lancet in January 2019, and generally settled on 25 to 29 grams a day.

Fiber is most commonly associated with improved bowel function, but it's so much more than just better poops. Researchers found that for every 8 gram increase of fiber eaten daily, deaths and incidents related to heart disease, Type 2 diabetes, and colorectal cancer decreased sometimes by as much as one quarter. A diet with more fiber in it also led to greater protection against stroke. Overall, the study found, people who consume more fiber are anywhere from 15% to 30% less likely to meet a premature death from chronic health conditions.

Nicola McKeown, an associate professor at the Friedman School of Nutrition Science and Policy at Tufts University, says the daily fiber intake of adults should be even higher. Citing recommendations handed down by the Food and Nutrition Board of the Institute of Medicine, she says that men under 50 should strive to eat 38 grams of fiber a day. (That's about a cup of chickpeas or two large bunches of broccoli.)

“Fiber can deliver a wide range of health benefits, including reducing blood cholesterol, reducing glucose levels, and keeping us regular by normalizing bowel function,” she says. (So, yeah, it's also better poops.)

Gut Check

In the Amazon rainforest, on the border between Venezuela and Brazil, lives a group of indigenous people called the Yanomami. With a total population of about 38,000, the Yanomami are the largest isolated group of indigenous people in South America. But the Yanomami are also known for something else: having the most diverse gut microbiome in the world, which is one of the cornerstones of good overall health.

“The Yanomami consume far higher amounts of fiber than we do in the U.S.,” says Noel Mueller, assistant professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health. “And they have no age-related rise in blood pressure.”

Inside the human gut are about 100 trillion different forms of bacteria, both good and bad. These are the microorganisms that, for instance, live in your colon and subsist on fiber. Maintaining your gut microbiome is crucial for maintaining your immune system.

“If we don’t consume enough dietary fiber, then our gut microbiota may have to rely on breaking down our gut mucosa for nourishment, which could potentially lead to having a leaky gut, when it becomes permissible to pathogenic microbes and toxins,” Mueller says.

Translated, what that means is that the dietary fibers we eat are broken down and metabolized by the bacteria in our guts. The byproducts of that breakdown can positively impact our health. But without enough fiber intake, the bacteria in our guts turn to eating the cells lining our intestines.

While the gut microbiome is as comprehensible as the Milky Way—scientists are still trying to determine the exact effect, if any, of gut-nourishing fibers on our overall immune health—the general rule for most Americans, Mueller says, is a simple one to follow.

“The more fiber, the better,” he says. “It’s foundational to a healthy diet."

Read More A Simple Rule for a Better Diet: Avoid Processed Foods

But don't throw away your canned beans just yet.

By Andrew Zaleski

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