The dietary fibre gap in the United States remains substantial, despite strong evidence linking fibre-rich diets with a lower risk of cardiovascular disease and colorectal cancer, as well as improved arthritis symptoms. Only 4% of US adults met recommended fibre levels between 2013 and 2018, with average consumption standing at about 16 grams a day.
Recommended daily intake is 25 grams for women and 38 grams for men. The shortfall has helped fuel growing interest in fibre-rich foods, supplements and products marketed as high in fibre.
However, the 2025 update to the American dietary guidelines has created confusion by placing high-fibre whole grains at the bottom of its inverted food pyramid, representing the smallest section. The written guidance continues to stress the importance of whole grains.
What dietary fibre does in the body
Dietary fibre is made up of carbohydrates that the body cannot digest. It is found in foods including raspberries, avocados, oats, other whole grains and lentils.
Fibre is also sold as a supplement, including psyllium husk powder. Isolated fibres such as inulin are increasingly added to snack bars, products marketed as keto-friendly carbohydrates and drinks.
Different types of fibre can have different effects. Psyllium is a viscous fibre that forms a gel when mixed with water, helping people feel fuller and potentially lowering cholesterol, improving blood sugar and blood pressure, supporting modest weight loss and making bowel movements more regular.
Other fibres are fermented by bacteria in the gut. These microbes produce proteins that can reduce inflammation in the body, while inulin is one example of a fermentable fibre that can be obtained from chicory root and Jerusalem artichokes.
Nutrition experts recommend eating a range of fibre-rich foods, which also provide other nutrients such as antioxidants, rather than relying on a single source.
Fibre and fermented foods
Fibre and probiotics support the gut in different ways. Fibre supplies material for bacteria already living in the gut, while probiotics provide additional live microbes through foods such as sauerkraut, yoghurt and kimchi.
A small 2021 study involving 36 healthy adults found that those following a high-fibre diet developed gut bacteria that were more active in producing enzymes to break down fibre. Participants eating more fermented foods developed a more diverse range of gut bacteria and had lower levels of inflammation.
The findings suggest that combining high-fibre and fermented foods may provide complementary benefits, although further research is needed to establish the most effective types, amounts and combinations of fibre.
How to increase dietary fibre
Cost, access and tolerability can all make it difficult to eat enough fibre. Berries, for example, can be expensive, while highly fermentable fibres such as inulin may cause bloating and discomfort, particularly among people who are not used to consuming them.
Increasing fibre gradually can give the body time to adjust. Staying hydrated is also recommended so the body has enough water to work with the fibre and support bowel health.
Some people may reach recommended levels through whole foods, while others may choose supplements or foods with added fibre. There is no single approach that suits everyone.
Jean Liew, assistant professor of medicine at Boston University, said more large and carefully designed clinical trials were needed to determine how fibre affects specific diseases and what dietary recommendations should be made.
Existing studies have established several health benefits, but the evidence does not yet answer every question about the ideal type or dose of fibre. Making high-fibre foods affordable and accessible, alongside educating the public, remains an important part of addressing the dietary fibre gap.
