Key Takeaways
- Most American adults consume roughly half the recommended daily amount of fibre.
- Fibre feeds beneficial gut bacteria, which plays a role in immune and metabolic health.
- Soluble fibre helps slow glucose absorption, supporting steadier blood sugar levels.
- Increasing fibre intake gradually — with adequate water — helps avoid digestive discomfort.
- Whole grains, legumes, vegetables, and fruits are among the richest everyday fibre sources.
Dietary Fibre
Dietary fibre is a type of carbohydrate found in plant foods that the human body cannot fully digest or absorb. Unlike sugars and starches, fibre passes relatively intact through the stomach and intestines, where it performs a range of important functions. It supports healthy digestion, feeds beneficial gut bacteria, helps regulate blood sugar, and contributes to feelings of fullness after eating.
Fibre is broadly classified as soluble (dissolves in water, forming a gel-like substance) or insoluble (does not dissolve, adding bulk to stool). Most whole plant foods contain a mix of both types, each with distinct physiological effects.
The Forgotten Nutrient in Plain Sight
Nutrition conversations tend to orbit protein, fat, and carbohydrates — the macronutrients that dominate food labels and diet debates alike. Fibre, technically a carbohydrate subtype, rarely gets the same attention, even though decades of research link adequate intake to lower risks of heart disease, type 2 diabetes, colorectal cancer, and all-cause mortality. Understanding what fibre actually does in the body makes it easier to see why it deserves a more prominent place in everyday eating decisions.
For a broader look at how all three macronutrients function together, see our guide to protein, carbohydrates, and fats.
~15g
Average daily fibre intake for US adults
According to data cited by the U.S. Dietary Guidelines Advisory Committee, average intake is roughly half the recommended amount for both men and women.
25–38g
Recommended daily fibre intake for adults
The Academy of Nutrition and Dietetics recommends 25g/day for women and 38g/day for men, based on estimates of adequate intake from U.S. dietary reference values.
19%
Reduced risk of type 2 diabetes with high fibre intake
A meta-analysis published in The Lancet (2019) found diets high in dietary fibre were associated with a 19% lower risk of developing type 2 diabetes compared to low-fibre diets.
What Fibre Actually Does in Your Body
Fibre's most widely recognised role is keeping digestion regular — insoluble fibre adds bulk to stool and speeds transit through the colon, reducing the time that waste material spends in contact with the intestinal lining. But its effects reach well beyond bowel habits.
Blood sugar regulation: Soluble fibre dissolves in water to form a viscous gel in the digestive tract, slowing the rate at which glucose from food enters the bloodstream. This blunting effect on blood sugar spikes is particularly relevant for reducing insulin demand after meals, and research published in journals like The Lancet has found high-fibre diets consistently associated with improved glycaemic markers.
Cardiovascular support: Soluble fibre — particularly beta-glucan found in oats — can bind to bile acids in the gut and promote their excretion. The liver then uses cholesterol to make more bile acids, which can modestly reduce circulating LDL cholesterol levels over time.
Satiety and appetite: Fibre slows gastric emptying (the rate at which food leaves the stomach), extending feelings of fullness. This mechanism is one reason high-fibre meals tend to reduce overall calorie intake without requiring deliberate restriction. See how this connects to daily energy management in our article on food and fatigue.
Increase Fibre Gradually to Avoid Discomfort
If your current diet is relatively low in fibre, a sudden large increase can cause bloating, cramping, or gas as your gut bacteria adjust. Add one or two new high-fibre foods per week rather than overhauling your diet at once. Drinking plenty of water alongside fibre-rich foods also helps the digestive process run smoothly.
Fibre and the Gut Microbiome
The colon is home to trillions of bacteria, collectively known as the gut microbiome. Many of these organisms ferment fibre — particularly the fermentable, soluble varieties — producing short-chain fatty acids (SCFAs) like butyrate, acetate, and propionate as byproducts. SCFAs serve as fuel for the cells lining the colon, help regulate immune responses, and may influence inflammation throughout the body.
Diets consistently low in fibre tend to reduce microbial diversity over time, a pattern that emerging research associates with a range of metabolic and inflammatory conditions. That said, this is still an active area of science, and establishing clear cause-and-effect relationships is complex. Our companion article on gut health and diet covers what the current evidence supports — and where uncertainty remains.
“Dietary fibre is not a single compound but a diverse family of plant components. The variety of fibre in your diet matters as much as the total amount, because different fibres feed different microbial species.”
— nutrition research consensus, Reflected across multiple systematic reviews on dietary fibre and the gut microbiome
Practical Ways to Eat More Fibre
Reaching adequate fibre intake does not require specialised foods or radical changes. The most fibre-dense options are also among the most affordable: legumes (lentils, chickpeas, black beans), whole grains (oats, barley, whole wheat), vegetables, and fruits with their skins on.
- Swap refined grains: Replacing white rice with brown rice or white bread with 100% whole-grain bread adds several grams of fibre per serving.
- Add legumes regularly: A half-cup of cooked lentils delivers around 8 grams of fibre. Adding them to soups, salads, or grain bowls is a low-effort, high-payoff habit.
- Keep fruit and vegetable skins on: The skin of apples, potatoes, and pears contains a significant share of the food's total fibre.
- Increase gradually: Jumping from a low-fibre diet to a high-fibre one too quickly can cause bloating and gas. Adding one or two high-fibre foods at a time, alongside adequate fluid intake, helps the gut adapt.
For evidence-informed habits you can build around these choices, see our article on nutrition habits worth building.
This article is for general informational and educational purposes only and is not a substitute for professional medical or dietary advice. Speak with a qualified healthcare provider before making significant changes to your diet, especially if you have an existing health condition.