Health guidelines recommend consuming between 30 and 40 grams of fiber daily. For women, the minimum recommended intake is 25 grams, while men should aim for 30 grams. But, a significant portion of the Dutch and roughly half of the Belgian population fall short of these targets. The situation in Spain is similar and potentially more concerning: national studies and dietary surveys indicate that the average fiber intake among Spanish adults ranges from 12 to 20 grams per day, depending on the group and methodology—well below the European recommendation of at least 25 grams daily.
These figures reveal that most of the Spanish population doesn’t even meet the minimum recommended fiber intake, often consuming less than 20 grams daily. This is true even in traditional diets based on the Mediterranean eating pattern, which naturally includes more fruits, vegetables, legumes, and whole grains. This shortfall is a public health concern, as adequate fiber intake is linked to numerous health benefits.
This occurs despite the fact that dietary fiber plays a key role in preventing diseases, including cardiovascular illness, certain cancers, and metabolic disorders, and is essential for maintaining a healthy gut microbiome. The benefits for health are particularly significant when different types of fiber are combined. But how does it work exactly?
Not All Fiber Works the Same Way
Reading a food label might lead someone to believe that fiber is simply fiber. However, it’s more complex than that. “Fiber is an umbrella term for a large group of complex carbohydrates,” explains Hannah Holscher, a nutritionist at the University of Illinois Urbana-Champaign.
“Because there are so many different types of fiber, they also do different things in the body.” Nutritionists generally differentiate between soluble and insoluble fibers.
Soluble vs. Insoluble Fiber
Soluble fibers dissolve in water and in the intestines. They are found in foods like oats, legumes, and fruits. They form a gel-like substance that helps reduce cholesterol, stabilize blood sugar levels, and promotes a feeling of fullness.
Insoluble fibers, such as the cellulose present in nuts, seeds, and whole-grain products, do not dissolve. Their primary function is to add bulk to stool and assist food move smoothly through the digestive tract. Both types are essential for proper intestinal function.
Fiber and the Gut Microbiome
Fiber does more than just promote intestinal transit. It plays a crucial role in maintaining a healthy gut microbiome. Especially soluble and fermentable fibers are broken down by gut bacteria.
During this process, short-chain fatty acids are generated—metabolic products that reduce inflammation, regulate the immune system, and improve nutrient absorption. “Many Western diseases are related to a dysregulated immune system,” explains Erica Sonnenburg, a microbiologist at Stanford University. “Fiber helps keep that system in balance.”
A lack of fiber is associated with chronic intestinal inflammation, autoimmune diseases, allergies, and with an increased risk of cardiovascular disease and colon cancer. Understanding these connections is vital for preventative healthcare.
Even Microplastics Are Affected
Increasing research shows that dietary fiber can also help eliminate harmful substances, including microplastics. According to microbiome researcher Katrine Whiteson, fibers form a kind of matrix that binds to toxic particles and expels them.
Exactly how this works is still under investigation. But the message is clear: variety is key. Holscher recommends “a wide mix of plant fibers” in the diet.
How Much Variety Is Needed?
Some studies show that people who consume more than thirty different plants per week tend to have a more diverse gut microbiome. For example, a large-scale study indicated that consuming more than thirty distinct plants per week is associated with greater microbial diversity. However, Whiteson emphasizes that a causal relationship has not yet been demonstrated .
“I’ve worked with communities in remote areas of Ecuador,” she says. “They have a very diverse microbiome, even though their food choices are quite limited.” The takeaway: eating more fiber is more important than having a perfect fiber menu.
Ultra-Processed Foods Don’t Help
Fiber is scarce in ultra-processed foods. Manufacturing processes designed to preserve, enhance flavor, or improve texture often come at the expense of fiber. For example, the bran is removed from white flour.
Some people turn to fiber supplements, but the evidence of their effectiveness is limited. Concentrated fiber can cause discomfort, such as bloating or diarrhea.
“It’s always better to eat a plant than to take a supplement,” says Holscher. “Plants contain, in addition to fiber, proteins, phytonutrients, and other substances that work together.”
Practical, Affordable, and Sustainable
For those looking to increase their fiber intake, it’s best to do so gradually and with plenty of water. People with gastrointestinal or intestinal problems should do so under the supervision of a specialist. Whiteson sums it up simply: “Look for something you like, that is affordable, and that you can eat daily. That’s the best way to address your fiber deficit.”
Roeliene works as an editor for National Geographic. As a science journalist, she also contributes to the magazines Quest and KIJK, among others. She loves traveling, religious history, and brisk walking.
