This is what really happens to your body when you don’t eat enough fibre

Despite the fact fibre is still overlooked by so many, a lack of it can wreak havoc on the body, particularly by causing digestive issues, affecting blood sugar, causing weight gain and making you feel tired. We asked registered nutritionist Rebecca Taylor to break it down for us.

Low fibre and your digestive system

Fibre plays a pivotal role in maintaining digestive health. When you don’t consume enough, the effects on your gut can be immediate and unpleasant.

“Fibre plays a key role in maintaining a healthy digestive system. Insoluble fibre adds bulk to stools and helps keep bowel movements regular, while soluble fibre supports gut bacteria by acting as a prebiotic,” explains Taylor. “A low-fibre diet can lead to constipation, bloating and an increased risk of conditions like diverticulitis and irritable bowel syndrome (IBS).”

Without adequate fibre you might notice your stools being smaller, harder and more difficult to pass. If this becomes chronic constipation, it can also cause things like haemorrhoids or anal fissures. A lack of fibre also disrupts your gut microbiome, as fibre serves as food for beneficial gut bacteria. “A healthy gut microbiome is essential for more than just digestion. Around 70% of our immune system resides in our gut,” explains registered nutritionist Zara Hiridjee. “Plus, certain gut bacteria produce short-chain fatty acids when they ferment fibre, which has been shown to reduce inflammation and support gut lining integrity.”

A fibre-deficient diet deprives these bacteria, potentially leading to dysbiosis, a state where harmful bacteria outnumber good bacteria. This imbalance can manifest as bloating, diarrhoea or increased susceptibility to gastrointestinal infections.

Over time, a low-fibre diet can raise your risk of serious digestive issues like diverticular disease. This condition involves the formation of small pouches in the colon that can become inflamed or infected. Studies also link low fibre intake with a higher risk of colorectal cancer, emphasising fibre’s long-term protective effects.

Low fibre and blood sugar

One of fibre’s key benefits is its ability to moderate the absorption of sugar into the bloodstream. When fibre is lacking, your body struggles to regulate blood sugar levels effectively.

“Fibre, particularly soluble fibre (found in oats, apples, bananas and avocados) slows the absorption of sugar into the bloodstream. This helps blunt spikes in blood sugar levels after meals,” explains Taylor. “Without enough fibre, carbohydrates are broken down and absorbed more quickly, leading to a rapid rise in blood sugar, followed by a crash. Over time, these fluctuations can contribute to insulin resistance and increase the risk of developing type 2 diabetes.”

Fibre also helps regulate cholesterol levels by binding to bile acids in the gut and preventing their reabsorption. A low-fibre diet may lead to higher cholesterol levels, exacerbating conditions like atherosclerosis, which is often linked to diabetes.

Low fibre and weight

Fibre is a secret weapon for weight management, and its absence can create challenges for those trying to maintain or lose weight. This is mainly because foods rich in fibre are more filling, according to Taylor. “They take longer to digest and help regulate appetite by promoting the release of satiety hormones. Without enough fibre, people may feel hungrier sooner, leading to overeating. Fibre also slows digestion, which helps maintain steady energy levels and reduces the likelihood of snacking on less nutrient-rich and more calorie-dense foods.”

Soluble fibre can also reduce some calorie absorption, according to a study in the British Medical Journal, because it forms a gel in the intestinal tract, which slows the absorption of digested protein, carbohydrate and fat into the bloodstream. This means those unabsorbed calories instead exit the digestive tract in faecal matter.

Blood sugar spikes and crashes can also result in cravings for sugary or high-fat foods to restore depleted energy levels. This can create a vicious cycle that is detrimental to weight management and overall health.

Low fibre and low energy

While fibre itself is not a source of energy, it supports a host of bodily functions that keep you feeling energised and alert. When your diet lacks fibre, fatigue may become a frequent companion.

“Fibre-rich foods, such as fruit, vegetables, wholegrains and legumes are nutrient powerhouses. A diet low in fibre is often also low in these key foods, potentially leading to deficiencies in essential vitamins and minerals like magnesium, B vitamins and iron,” Taylor says. “These nutrients are vital for energy production, so their absence can contribute to feelings of fatigue and brain fog. Additionally, blood sugar fluctuations from low fibre intake can leave you feeling drained.”

A fibre-packed diet can help maintain steady energy levels by moderating your digestion. This is why you might find yourself struggling to do sustained periods of physical activity.

What foods are rich in fibre?

It is important to get fibre from a variety of sources, as eating too much of one type of food may not provide you with a healthy balanced diet. But it’s simple to add fibre into your daily diet through breakfast, lunch, dinner and snacks. Fibre-rich foods include:

• Wholegrains such as wholewheat bread and pasta, porridge oats and bran flake cereals
• Legumes including lentils, chickpeas, black beans and kidney beans
• Fruits like berries, skin-on apples, oranges, pears and avocado
• Vegetables such as carrots, broccoli and spring greens
• Skin-on potatoes
• Onions and garlic

Fibre is more than just a tool for staying regular, it is an essential nutrient that affects everything from blood sugar regulation to weight management and energy levels. A low-fibre diet doesn’t just deprive your digestive system, it can throw your entire body off kilter.

By prioritising fibre-rich foods, you can help your digestive health, maintain balanced blood sugar levels and feel energised throughout the day. If you’re currently eating a low-fibre diet, gradually increasing your intake while drinking plenty of water can make the transition smoother and more effective.