Fibre & blood sugar: the underrated lever on your plate

Fibre is a carbohydrate the body can’t digest. That’s exactly what makes it valuable: it barely delivers glucose to the blood but positively influences how other nutrients are absorbed.

Two types with different effects

We distinguish soluble and insoluble fibre.¹ Soluble fibre – such as beta-glucan from oats and barley – forms a viscous gel in the gut. This gel slows sugar uptake and thus dampens the blood-sugar spike.¹² Insoluble fibre mainly aids digestion and is linked with a lower diabetes risk.²

What the studies show

Evidence level: established (meta-analysis)

A meta-analysis found that soluble (viscous) fibre in a typical amount of about 13 g per day – roughly a tablespoon – can lower HbA1c by around 0.6% on average.³ A high fibre intake is also linked with lower mortality in large cohort studies.⁴

How much makes sense?

Professional bodies recommend roughly 25 g per day for women and 30–38 g for men.¹ In reality, many people eat only about 15 g – so there’s a lot of untapped potential here. Good sources are oats, legumes, vegetables, fruit with skin and wholegrain products.

How fibre slows blood sugar

The effect works three ways. First, soluble fibre (in oats or legumes) forms a viscous gel in the stomach that slows gastric emptying and glucose absorption – the curve after eating becomes flatter. Second, insoluble fibre adds volume and satiety without becoming sugar itself. Third, fibre is fermented by bacteria in the colon, producing short-chain fatty acids that feed the microbiome and can support insulin sensitivity.

How to build it in – without bloating

Suddenly eating a lot more fibre often causes bloating. So: increase slowly, give the gut a few weeks, and drink enough – without water, fibre can be constipating. A practical start is the order on your plate: vegetables and protein first, then the carbs.