Key Takeaways
- Most US adults consume only about half the recommended daily amount of dietary fibre.
- Fibre supports gut health, blood sugar regulation, and cardiovascular health.
- Whole grains, legumes, fruits, and vegetables are the most effective fibre sources.
- Both soluble and insoluble fibre serve distinct but complementary roles in the body.
- Increasing fibre intake gradually — alongside adequate water — minimises digestive discomfort.
Dietary Fibre
Dietary fibre is a type of carbohydrate found in plant foods that the human body cannot fully digest or absorb. Unlike proteins, fats, or other carbohydrates, fibre passes largely intact through the digestive system, where it performs several important functions. It supports healthy digestion, helps regulate blood sugar, and feeds beneficial gut bacteria.
Fibre is classified into two main types — soluble (which dissolves in water to form a gel-like substance) and insoluble (which adds bulk to stool). Most plant foods contain a mix of both.
The Fibre Gap: Why It Matters
Despite decades of public health messaging around eating more fruits, vegetables, and whole grains, dietary fibre remains one of the most consistently under-consumed nutrients in the United States. The gap between recommended and actual intake is wide enough that the DGA has identified fibre as a nutrient of public health concern. Understanding why this matters begins with understanding what fibre actually does inside the body.
~15g
Average daily fibre intake for US adults
According to data cited in the Dietary Guidelines for Americans, the average adult consumes roughly 15 grams per day — about half the recommended amount.
25–38g
Recommended daily fibre intake for adults
The Dietary Guidelines for Americans recommend 25 grams daily for women and 38 grams for men, with needs varying by age and calorie intake.
95%
US adults not meeting fibre recommendations
Research published in nutrition journals estimates that approximately 95% of Americans fail to meet recommended daily fibre intake levels.
Fibre is technically a carbohydrate, but it behaves very differently from sugars and starches. To understand how it fits into the broader picture of what you eat, see our guide to macronutrients for an overview of how the body uses different food components.
Soluble vs. Insoluble Fibre: Two Types, Two Jobs
Soluble fibre dissolves in water to form a viscous gel in the digestive tract. This slows the absorption of glucose, which can help moderate blood sugar responses after meals, and it binds to bile acids in the gut — a process linked to modest reductions in LDL (low-density lipoprotein) cholesterol levels. Oats, barley, apples, citrus fruits, and legumes are reliable soluble fibre sources.
Insoluble fibre does not dissolve. It adds physical bulk to stool, reduces transit time through the colon, and is associated with a lower risk of constipation. Whole wheat, nuts, seeds, and many vegetables — including broccoli and carrots — are good sources.
Increase Fibre Gradually for Comfort
If your current fibre intake is low, aim to increase it by around 5 grams per week rather than all at once. Pairing the increase with adequate water intake — typically at least 8 cups per day — helps fibre move effectively through the digestive system and reduces the likelihood of gas or bloating.
Most plant foods contain a combination of both types. Focusing on variety across whole plant foods, rather than tracking each fibre subtype, is a more practical approach for most people.
What Research Links Fibre To
A substantial body of evidence associates higher fibre intake with a range of health outcomes. Epidemiological research has consistently linked diets rich in fibre to lower rates of type 2 diabetes, cardiovascular disease, and colorectal cancer, though it is important to note that diet patterns are complex and fibre alone is rarely the sole variable.
“Dietary fibre is not a single nutrient but a diverse family of compounds, each interacting with the gut in distinct ways. The variety of fibre in the diet may matter as much as the total amount.”
— David Katz, Physician and founding director of the Yale-Griffin Prevention Research Center
Fibre also plays a key role in gut microbiome health. Certain fibres — often called prebiotics — are fermented by beneficial bacteria in the colon, producing short-chain fatty acids that support the intestinal lining and immune function. This is an area of active research, and the full implications are still being explored.
When thinking about the relative value different foods offer, the concept of nutrient density vs. calorie density can be a useful lens — high-fibre whole foods often rank well on both measures.
The Best Food Sources of Dietary Fibre
No single food provides all the fibre variety the gut needs, which makes dietary diversity important. The following categories are among the most effective sources:
- Legumes: Lentils, chickpeas, and black beans deliver 12–15 grams of fibre per cooked cup — among the highest of any food.
- Whole grains: Oats, barley, quinoa, and whole wheat bread provide both soluble and insoluble fibre, along with B vitamins and minerals.
- Fruits: Raspberries, pears, and apples (with skin) are particularly fibre-dense relative to their size.
- Vegetables: Artichokes, broccoli, Brussels sprouts, and carrots are standout sources among common vegetables.
- Nuts and seeds: Chia seeds and flaxseeds are especially concentrated sources and can be added easily to existing meals.
You can learn more about spotting fibre content on product packaging in our guide to reading a nutrition label.
Practical Ways to Close the Gap
Increasing fibre intake does not require overhauling an entire diet overnight. Abrupt large increases can cause bloating and gas as the gut microbiome adjusts — a gradual approach over several weeks tends to be more comfortable and sustainable.
Some effective, evidence-aligned strategies include swapping refined grains for whole grain versions, adding a serving of legumes to soups or salads a few times per week, keeping the skin on fruits and vegetables where appropriate, and choosing whole fruit over juice. Drinking enough water is also important, since fibre absorbs fluid and works more effectively in a well-hydrated digestive system.
It is worth noting that not all nutrition claims around fibre are accurate. For a broader look at where popular nutrition messaging diverges from the evidence, see our examination of common nutrition myths.
This article is for general informational purposes only and does not constitute medical or dietary advice. Speak with a registered dietitian or qualified healthcare professional for guidance tailored to your individual health needs.