Low fibre diets affect more than digestion, US doctor explains their impact on overall health

Fibre has long been recognised as a cornerstone of a balanced diet, but growing evidence suggests its role extends far beyond simply keeping digestion regular.

From helping regulate cholesterol levels and stabilise blood sugar to supporting gut bacteria and reducing the risk of colon cancer, fibre influences multiple systems within the body.

Despite its wide-ranging benefits, many people still fall short of the recommended daily intake, often unaware of the silent impact this can have over time.

Dr Kunal Sood, an anaesthesiologist and interventional pain medicine physician, is breaking down the far-reaching implications of low fibre intake, highlighting its effects beyond just digestion.

In an Instagram video shared on 1 March, the physician explains, "Low fibre intake does not just slow bowel movements. It alters bile acid handling, glucose absorption, gut microbiota fuel and long-term colon health.

Fibre supports cholesterol handling, glucose control, microbiome balance and colon integrity. Chronically low intake affects all of these systems long before symptoms appear."

Rise in LDL cholesterol

According to Dr Sood, soluble fibre forms a gel-like substance in the gut that binds to bile acids and cholesterol.

As these are excreted, the liver is prompted to draw more cholesterol from the bloodstream to produce additional bile acids, thereby helping to lower circulating cholesterol levels.

He explains, "Soluble, viscous fibres such as beta-glucan and psyllium form a gel that traps bile acids and cholesterol in the gut. This increases bile acid excretion, forcing the liver to pull cholesterol from the bloodstream to make more bile acids. Controlled-trial meta-analyses show meaningful LDL reductions with several major fibres."

Higher post-meal glucose spikes

Eating fibre also slows gastric emptying, thereby delaying the digestion and absorption of carbohydrates.

However, without adequate fibre intake, the physician notes that glucose enters the bloodstream more rapidly, resulting in sharp spikes in blood sugar and insulin levels.

He elaborates, "Viscous fibre slows gastric emptying and creates a diffusion barrier, meaning carbohydrates are digested and absorbed more gradually. Without enough fibre, glucose enters the bloodstream faster, producing higher peaks and larger insulin responses. Mechanistic and systematic reviews support this glycaemic effect."

Shift in gut bacteria and mucus barrier

Dietary fibre also serves as prebiotic fuel for beneficial gut bacteria, and chronically low intake can disrupt the microbiome, potentially leading to imbalances and a thinning of the protective mucus lining of the gut.

Dr Sood explains, "Many gut microbes rely on microbiota-accessible carbohydrates, a key component of dietary fibre. When fibre intake is chronically low, microbes shift toward degrading host mucus glycans, thinning the protective mucus layer. An animal model showed fibre deprivation led to mucus barrier degradation and greater pathogen susceptibility."

Increased risk of colon cancer

Dr Sood highlights that consistently low fibre intake may increase the risk of colon cancer over time.

Fibre adds bulk to the stool and promotes faster intestinal transit.

It also supports bacterial fermentation into short-chain fatty acids, which help protect the epithelium and maintain gut health — collectively lowering the risk of colon cancer.

He emphasises, "Large prospective dose-response analyses show about a 10% lower colorectal cancer risk per 10 g/day higher fibre intake. Proposed mechanisms include increased stool bulk and faster transit, fermentation to short-chain fatty acids like butyrate that support epithelial health and altered bile acid profiles that may be less irritating to the colon."