The American Fiber Gap 🥦

As someone who follows a vegetarian diet and sometimes eats multiple portions of beans a day, I was surprised to find out that most Americans are not getting enough fiber in their diets. Fiber is a type of carbohydrate that passes through the body undigested. Though perhaps best known for its role in supporting regular bowel movements, fiber also offers several significant health benefits.

alt text: An array of fruits, vegetables, nuts, and seeds.

“Adequate intake of dietary fiber is associated with digestive health and reduced risk for heart disease, stroke, hypertension, certain gastrointestinal disorders, obesity, type 2 diabetes, and certain cancers.” This is due to its numerous benefits: it slows down glucose absorption, helps to stabilize blood sugar levels, and also contributes to lower cholesterol and reduced inflammation. 

The Dietary Guidelines for Americans have identified fiber as a “nutrient of concern” since 2005 because of the significant gap between total fiber intake and fiber recommendations. In 2021, it was found that only 5% of men and 9% of women in America are getting the recommended daily amount of dietary fiber. On average, American adults consume between 10 to 15 grams of total fiber daily. The USDA recommends that adults under 50 years old aim for 25 grams of fiber each day for women and 38 grams for men. For those over 50, the recommended amounts decrease to 21 grams for women and 30 grams for men.

This is an issue that is impacting Americans, but even more specifically, non-Hispanic Black adults. A 2014 study conducted by the Alliance for Potato Research and Education found that non-Hispanic Black adults consumed 21% less dietary fiber compared to the overall U.S. adult population. On average, Black adults were getting only 44% of the recommended daily intake of fiber.

alt text: Shawn Baker eating a large steak.

What is causing fiber to be a “nutrient of concern” in America? There are a few factors at play. Firstly, because of gym culture and fad diets, Americans are preoccupied with protein and carb consumption. When we think about the deterioration of the American diet, the focus is often on the excessive amounts of sugar, salt, and calories rather than on whether enough fiber is being ingested. According to nutritionist Julie Jones, “People are so busy avoiding carbs, they forget that these [fiber-rich] foods give [them] important dietary components.” 

Another reason we aren’t consuming enough fiber is because our food culture revolves around ultra-processed foods. Rather than enjoying fruits, vegetables, beans, nuts, and seeds, over 50% of the calories consumed by Americans come from ultra-processed foods. On any typical day, almost 40% of Americans consume some form of fast food. These ready-made and processed meals usually lack fiber or contain very little of it. For example, a cup of cooked oatmeal has 4 grams of fiber, a pear has 6 grams, but a McDonald’s hamburger contains just 1 gram, and soda has none at all.

Throughout history, humans have evolved to eat plentiful amounts of fiber. Tanzania’s Hadza people are one of the few remaining hunter-gatherer groups on the planet. Their diets are a useful model for understanding just how much fiber early humans probably ate. Members of this tribe consume between 100 and 150 grams daily—equivalent to about 50 bowls of Cheerios and ten times the amount typically consumed by Americans. Their diet is abundant in roughage, consisting of tubers, berries, and baobab fruits—and they don’t eat any ultra-processed foods.

“It’s really just within the last 5,000 years, and definitely within the last 100 years, that we basically took all the fiber away,” researcher Jens Walter at the University of Alberta said. “The average amount of fiber consumed by now is a small fraction to what we evolved with.” Another factor is that our diets have also transitioned to become more meat-centered. Meat has replaced fibrous beans and lentils as the main source of protein in many parts of the world. 

You might be wondering how a lack of fiber actually affects your digestive system. In a study conducted by Georgia State University, researchers put one group of mice on a fiber-enriched high-fat diet and another on a low-fiber high-fat diet. The two sets of mice ended up having really different microbiomes. Rodents on the low-fiber diet had a marked reduction in the total number of bacteria in their gut and a less diverse microbiome compared to the mice on the high-fiber diet. 

Andrew Gewirtz, one of the researchers, explained that a lack of diversity in our gut microbiome can negatively impact health, particularly concerning the mucus layer that protects our intestines. This mucus, replenished by intestinal cell secretions, is covered with bacteria from our microbiome. Fiber nourishes these bacteria, maintaining a healthy microbiome. Another study in mice found that bacteria began to eat away at the mucus layer, bringing them into closer contact with the intestinal tissues when the bacteria in the digestive tract didn’t get any fiber. “The hypothesis is if we stop feeding the microbiome [fiber], the bacteria will resort more frequently to digesting that mucus barrier as a source of nutrients.” 

alt text: Mouse nibbling on corn on the cob.

If bacteria eating up the mucus layer sounds bad, well, it is. Bacteria that break down the mucus layer can worsen infections by allowing pathogens easier access to the intestine (especially on a low-fiber diet). Without the mucus barrier, diseases progress more quickly and can irritate intestinal tissue or trigger immune responses, increasing vulnerability to illness.

What can you do to prevent this?

Fiber consumption can begin as early as your morning breakfast. I like to put seeds, nuts, and berries in my morning yogurt to increase my fiber intake. If you don’t have access or the budget for fresh fruit, seeds and nuts are still a great option. They are economical, last on the shelf forever, and are a great source of fiber and nutrients. 

alt text: Bowl of Greek yogurt topped with seeds and raspberries.

Throughout the day, you can also be more mindful of what you are eating. Choose breads, pastas, and cereals made from whole grains, as well as brown rice. Eat fruits like apples and oranges instead of drinking their juice. Try to include vegetables with every meal—especially fibrous beans, peas, and lentils. Opt to snack on nuts, fruits—such as strawberries, raspberries, and blackberries—and popcorn.

Important tips as you increase your fiber

Make changes slowly to allow your gastrointestinal system to adjust. As you raise your fiber intake, be sure to also drink more water. If you experience any digestive issues, talk to your doctor before making significant increases in your fiber intake.

To conclude, fiber doesn’t just help us poop better, it nourishes our gut microbiome. Dietary fiber intake is associated with a decreased risk of death from any cause. Those eating the highest amount of fiber reduced their risk of dying by 23% compared to those eating the least amount of fiber. Another benefit of high-fiber diets is weight control. By helping you feel full longer after a meal or snack, high-fiber whole grains can help you eat less. 

Current fiber intakes are alarmingly low, with long-term implications for public health. However, making small, mindful changes to our diets to increase fiber every day can have an immense, positive effect on our collective health.