Fiber is both diet fad and fixture for good health – a doctor explains why there is no one-size-fits-all way to increase your intake

Most Americans do not consume enough dietary fiber, which is essential for health. The recommended daily intake is 25 grams for women and 38 grams for men, but from 2013 to 2018, only 4% of U.S. adults met these targets. On average, Americans consume about 16 grams of fiber per day. This shortfall is called the fiber gap. Fiber is found in plant-based foods like whole grains, fruits, vegetables, legumes, nuts, and seeds. It is a type of carbohydrate that the body cannot digest, yet it plays a critical role in maintaining digestive health, regulating blood sugar, and supporting heart health. Despite its benefits, fiber is often overlooked in favor of other nutrients, leading to widespread deficiency in the American diet.

Dietary fiber is not a single substance but a diverse group of carbohydrates with different properties and health effects. Fiber can be classified into two main types: soluble and insoluble. Soluble fiber dissolves in water and forms a gel-like substance, which can help lower cholesterol and stabilize blood sugar. Examples include psyllium husk, oats, and beans. Insoluble fiber does not dissolve and adds bulk to stool, aiding digestion and preventing constipation. Examples include wheat bran and many vegetables. Some fibers are also fermentable, meaning gut bacteria can break them down, producing beneficial compounds like short-chain fatty acids that reduce inflammation. The type of fiber matters because each has unique benefits for health.

High-fiber diets are linked to significant health benefits, including a lower risk of cardiovascular disease, colorectal cancer, and improved arthritis symptoms. Fiber helps manage weight by promoting feelings of fullness, which can reduce overeating. It also supports gut health by feeding beneficial gut bacteria, which produce substances that reduce inflammation. For example, viscous fibers like psyllium can improve bowel regularity and lower cholesterol. Fermentable fibers, such as inulin found in chicory root, support a diverse gut microbiome, which is associated with better immune function and lower inflammation. These benefits highlight why fiber is considered a cornerstone of a healthy diet.

Fiber and probiotics are often mentioned together in discussions about gut health, but they work differently. Fiber provides the material that gut bacteria ferment to produce beneficial compounds. Probiotics, on the other hand, are live microorganisms found in fermented foods like yogurt, sauerkraut, and kimchi. These foods contain good bacteria or yeast that can directly add to the gut microbiome. While fiber feeds the existing bacteria, probiotics introduce new bacteria. A 2021 study found that a diet high in fermented foods increased the diversity of gut bacteria and reduced inflammation, while a high-fiber diet enhanced the activity of fiber-digesting enzymes in gut bacteria. Combining both may offer synergistic health benefits.

Despite its benefits, increasing fiber intake can be challenging due to several barriers. Cost is a major factor, as some high-fiber foods like berries and nuts are expensive. Accessibility is another issue, as fresh produce and whole grains may not be readily available in all communities. Tolerability is also a concern, as highly fermentable fibers like inulin can cause bloating, gas, and discomfort, especially for those unaccustomed to high-fiber diets. Additionally, many fiber-rich foods require preparation, which can be time-consuming. These challenges explain why many people struggle to meet recommended fiber intake levels, even when they are aware of the benefits.

To increase fiber intake gradually, experts recommend starting with small amounts and slowly increasing over weeks to allow the gut to adapt. Staying hydrated is crucial, as fiber absorbs water and helps move waste through the digestive system. Choosing a variety of fiber sources is also important, as different fibers offer unique health benefits. Whole foods like oats, lentils, raspberries, and avocados are excellent choices. For those who struggle to meet fiber goals through food alone, supplements like psyllium husk can help. However, it is essential to find what works best for individual needs, as there is no one-size-fits-all approach to fiber intake.