Fibre: The Nutrient Most People Undereat and Why It Matters

Why Fibre Keeps Getting Overlooked

Fibre rarely commands the attention that protein or omega-3 fatty acids do, yet it is one of the most consistently under-consumed nutrients in the American diet. National nutrition surveys suggest the average US adult takes in roughly 15 grams of fibre daily — well below the 25–38 grams that health authorities recommend depending on age and sex.

Part of the reason is structural. Processed and refined foods — which make up a large share of the typical American diet — have had much of their fibre removed during manufacturing. White bread, for example, contains far less fibre than whole wheat bread made from the same grain. As ultra-processed foods have become more convenient and affordable, fibre intake has quietly declined.

Understanding fibre matters not just for digestion, but because its effects reach far beyond the gut. This article explains what fibre does, why the shortfall is consequential, and how to realistically eat more of it. For a broader look at how fibre fits within the full picture of healthy eating, see our complete nutrition resource.

What Fibre Actually Does in the Body

Fibre's best-known role is keeping digestion moving. Insoluble fibre adds bulk to stool and speeds transit time through the colon, which helps prevent constipation. Soluble fibre, found in oats, beans, and apples, dissolves in water to form a viscous gel that slows the movement of food through the small intestine. This slowing effect has meaningful downstream consequences.

When digestion slows, glucose from carbohydrates enters the bloodstream more gradually, resulting in a gentler rise in blood sugar. This is why high-fibre diets are consistently associated with better blood sugar control in research literature. The gel formed by soluble fibre also binds to bile acids in the gut — substances the body makes from cholesterol — and carries them out of the body. To replace those bile acids, the liver draws on circulating cholesterol, which may help explain the well-documented link between soluble fibre intake and lower LDL cholesterol levels.

Fibre also feeds the trillions of bacteria that make up your gut microbiome. Fermentable fibre — found in foods like onions, garlic, and legumes — serves as a prebiotic, fuelling beneficial bacterial strains that produce short-chain fatty acids. These compounds have been linked to reduced gut inflammation and may play a role in immune regulation, though research in this area continues to evolve.

“Dietary fibre is one of the most important — and most neglected — components of the diet. The evidence linking adequate fibre intake to reduced risk of cardiovascular disease, type 2 diabetes, and colorectal cancer is among the most consistent in nutrition research.”

— Walter Willett, Professor of Epidemiology and Nutrition, Harvard T.H. Chan School of Public Health

The Best Everyday Sources of Fibre

No single food delivers all the fibre your body needs, and different sources tend to supply different types. Variety is the most practical strategy. Below are the most fibre-dense everyday categories:

• Legumes: Lentils, black beans, chickpeas, and split peas are among the most concentrated fibre sources available — a cooked half-cup of lentils provides roughly 8 grams.
• Whole grains: Oats, barley, bulgur, and whole wheat bread contribute both soluble and insoluble fibre. Checking the nutrition label for grams of fibre per serving is a practical guide; reading a nutrition label can help you decode those figures accurately.
• Vegetables: Broccoli, Brussels sprouts, carrots, and artichokes are particularly fibre-rich. Most vegetables contribute meaningfully when eaten in whole form rather than juiced.
• Fruits: Pears, apples, berries, and avocados provide fibre alongside vitamins and beneficial plant compounds. Eating the whole fruit rather than drinking juice preserves the fibre content.
• Nuts and seeds: Almonds, chia seeds, and flaxseeds deliver fibre alongside healthy fats, making them easy additions to meals or snacks.

Fibre-rich foods also tend to be excellent sources of vitamins and minerals — another reason micronutrient intake often improves alongside fibre intake when people shift toward more whole plant foods.

How to Increase Fibre Without Digestive Discomfort

A sudden large increase in fibre intake often causes gas, bloating, or cramping as gut bacteria rapidly ferment unfamiliar substrates. Gradual change is more sustainable and comfortable. Adding one or two high-fibre foods per week — rather than overhauling the entire diet overnight — gives the microbiome time to adapt.

Hydration matters here. Fibre absorbs water as it moves through the digestive tract, so inadequate fluid intake can worsen rather than relieve constipation when fibre goes up. The connection between hydration and digestion is explored further in our article on hydration and nutrition.

Simple, sustainable swaps include choosing whole grain bread over white bread, adding a handful of beans to soups or salads, or swapping refined breakfast cereals for oats. These are modest changes individually, but they compound meaningfully across a full day of eating.

If you are experiencing persistent digestive symptoms or have an existing gastrointestinal condition such as irritable bowel syndrome, Crohn's disease, or diverticular disease, speak with a gastroenterologist or registered dietitian before significantly increasing fibre intake. Guidance tailored to your condition will be more appropriate than general population recommendations.

This article is for general informational and educational purposes only and is not medical or dietary advice. Please consult a qualified healthcare professional before making significant changes to your diet or if you have concerns about your nutritional health.