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A bowl of white rice topped with stir-fried chicken and vegetables, including red, green, and yellow bell peppers, garnished with chopped green onions, on a blue surface with a second bowl of similar stir-fry in the background.
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Fibre and the Gut Microbiota

Dietary fibre is gaining attention for its important role in improving metabolic health and reducing inflammation, two key factors in conditions like obesity and type 2 diabetes. Gut microbes help break down dietary fibre through fermentation, producing beneficial compounds like short-chain fatty acids (SCFAs). These microbes respond rapidly to dietary changes, with fibre intake reshaping their composition sometimes within just two days.

Soluble fibres are fermented in the colon, producing SCFA’s, whereas insoluble fibres ferment more slowly but still contribute to microbial diversity and gut health. The fermentation process helps balance bacteria ratios, increases microbial diversity, and boosts beneficial species. Soluble fibre, in particular, may help improve metabolic markers and support weight loss in people with metabolic health conditions including type 2 diabetes.

Fibre Tyres

Fibre comes in two main forms, and each plays a unique role in the body:

  • Soluble fibre is found in fruits, vegetables, oats, barley, wheat, and legumes. It forms a gel-like substance in the gut, slowing digestion, reducing glucose absorption, supporting immune function, and lowering cholesterol levels

  • Insoluble fibre, mainly cellulose, is present in legumes, whole grains, and many fruits and vegetables. It adds bulk to stool, softens it, and helps regulate bowel movements. Unlike soluble fibre, it ferments more slowly in the colon.

Fibre Intake in the UK

According to the British Nutrition Foundation, the recommended daily intake of fibre is 30g for adults and adolescents over 16. However, most people in the UK consume only about 20g per day. The main sources of fibre for UK adults are:

  • Cereals and cereal products (38%)

  • Vegetables and potatoes (30%)

  • Meat and meat products (11%)

  • Fruit (8%)

Supporting Metabolic Health

Short-chain fatty acids (SCFAs) influence important pathways in the body, including metabolism, inflammation, and brain function. They help regulate insulin signalling, reduce fat storage in fat tissue, and improve insulin sensitivity, which if not controlled are risk factors for obesity and type 2 diabetes.

SCFAs also help maintain the gut barrier by strengthening the mucus lining (part of the gut wall) and preserving tight junctions (barriers) between cells, which protect against inflammation and oxidative stress.

Fibre-driven SCFA production also encourages the growth of beneficial gut bacteria while limiting harmful ones, contributing to fibre’s anti-inflammatory effects.

Daily Diversity for Microbial Health

What you eat over time affects the bacteria in your gut. Diets high in protein and fat usually support bacteria like Bacteroides. Diets rich in carbohydrates often help bacteria like Prevotella grow. Eating a lot of fibre can lower inflammation by reducing certain chemicals from fat cells and boosting helpful bacteria.

A 10-week randomized controlled trial involving 75 overweight or obese women tested fibre from wholegrains, fruits, vegetables, or a mix. All groups showed improvements in insulin and blood glucose, but the wholegrain group saw the greatest reduction in inflammation markers. Another study of 22 randomised controlled trials found that soluble fibre supplementation alone, significantly reduced body weight, BMI, waist circumference, insulin resistance, and fasting insulin levels, matching the effects of combined dietary and weight management interventions.

While processed foods with added fibre or supplements can help meet daily targets, they shouldn’t be the main source. Whole foods offer more than just fibre as they are lower in calories and rich in essential nutrients and compounds like polyphenols that nourish gut microbes.

Diet Approach

SCFA levels and quality depend heavily on diet. A fibre-rich diet, especially one with a variety of complex carbohydrates, including legumes, wholegrains and whole-wheat bread and rice, boosts microbial diversity and SCFA production. This diversity helps shape a healthier gut microbiome, which in turn supports better metabolic and cognitive outcomes.

In short, choosing fibre-rich foods can enhance SCFA production, strengthen gut health, and protect against chronic conditions like obesity and neurodegenerative diseases. A wide-range of fibre filled whole foods provides different fuel sources for the gut microbiome, helping to build a diverse and resilient bacterial ecosystem.

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