The Fibre Gap: Why Most People Don't Eat Enough and What That Means

The Scale of the Fibre Gap

Despite fibre being one of the most researched and consistently recommended dietary components, intake across the US population falls well short of guidelines. Data from national nutrition surveys suggest the average American eats around 15–16 grams of fibre per day — roughly half of what is typically advised for adults.

This shortfall is sometimes called the "fibre gap," and it reflects broader patterns in modern eating: diets heavy in ultra-processed foods, refined grains, and animal products, with relatively few whole plant foods. The gap is not a personal failing — it is a structural feature of the food environment most people navigate daily.

Fibre deficiency does not usually announce itself the way a vitamin deficiency might. Instead, its effects accumulate quietly: irregular digestion, unstable blood sugar, and, over time, elevated risk of chronic disease. Understanding what fibre actually does is the first step toward appreciating why the gap matters.

What Fibre Does Inside Your Body

Fibre's main job is to move through your digestive system doing structural work rather than providing calories. Soluble fibre, found in oats, apples, and legumes, absorbs water and forms a thick gel in the gut. This gel slows digestion, which helps steady the release of glucose (sugar) into the bloodstream — an important mechanism for blood sugar regulation.

Insoluble fibre, found in wheat bran, most vegetables, and whole grain foods, does not dissolve. Instead, it adds bulk and encourages food to move more efficiently through the intestines, supporting regularity and reducing constipation.

A third category — fermentable fibre — deserves special mention. Certain fibres, including those in garlic, onions, legumes, and oats, are fermented by bacteria in the large intestine. This fermentation produces short-chain fatty acids that feed the gut lining and support a healthy microbiome. For a deeper look at how your gut uses food, see our guide on gut health and diet.

Where Fibre Actually Comes From

All dietary fibre comes from plants. Animal products — meat, dairy, eggs, fish — contain none. This matters because diets that are heavily animal-based without intentional inclusion of plant foods will almost always fall short on fibre.

Whole grains are one of the most accessible fibre sources: oats, barley, brown rice, quinoa, and whole wheat bread all contribute meaningfully. Legumes — lentils, chickpeas, black beans, and kidney beans — are among the most concentrated sources available. Fruits and vegetables vary widely; apples, pears, broccoli, carrots, and Brussels sprouts tend to rank higher than iceberg lettuce or cucumber.

Nuts and seeds also contribute, with chia seeds, flaxseeds, and almonds being particularly notable. Eating a variety of these foods across the day, rather than relying on any single item, tends to cover both soluble and insoluble needs more effectively.

It is also worth noting that fibre is not evenly distributed throughout a plant food. Apple skin contains far more fibre than apple juice. Potato skins contribute more than mashed potato. Minimally processed, whole-form foods consistently outperform their refined or juiced counterparts.

Health Consequences of Consistently Low Fibre Intake

Research consistently links low fibre consumption with several health concerns. Constipation is the most immediate and widely recognised — without enough insoluble fibre and fluid, stool becomes harder to pass. But the longer-term associations are more significant.

Lower fibre diets are associated with higher rates of type 2 diabetes, cardiovascular disease, and certain gastrointestinal conditions. Soluble fibre in particular is linked to modest reductions in LDL ("bad") cholesterol, a known risk factor for heart disease. Disruptions to the gut microbiome from inadequate fermentable fibre may also have downstream effects on immune function and inflammation, though research in this area is still evolving.

Fibre deficiency does not operate in isolation — it often accompanies lower intake of other beneficial plant compounds. Our related explainer on micronutrient deficiencies covers the overlap between nutrient-poor diets and common shortfalls.

This article is for general informational purposes only and does not constitute medical or dietary advice. Consult a qualified healthcare professional or registered dietitian for guidance specific to your health needs.

Practical Ways to Close the Gap

The most evidence-backed approach to increasing fibre intake is straightforward: add more whole plant foods to everyday meals. A few practical adjustments can make a meaningful difference without requiring a complete dietary overhaul.

• Swap refined grains for whole grains — choose whole wheat bread, oats, or brown rice in place of white versions.
• Add legumes regularly — lentils and beans can be added to soups, salads, and grain bowls with minimal effort.
• Eat fruit whole rather than juiced — preserving the skin and flesh retains far more fibre.
• Keep vegetables varied and minimally processed — raw or lightly cooked vegetables retain more fibre than heavily processed ones.
• Increase intake gradually — jumping from very low to high fibre quickly can cause gas and bloating. A steady increase over several weeks is easier on the gut.
• Drink plenty of water — fibre works best when adequately hydrated; insufficient fluid intake can worsen rather than improve digestive comfort.

If you want to take a broader look at your eating patterns, our weekly nutrition self-check offers a structured way to reflect on your current habits, including fibre, hydration, and variety.