Many of us could be suffering from a rapidly ageing brain caused by fibre deficiency – a dietary flaw that could explain why Alzheimer’s and dementia are the leading causes of death in the UK. That’s according to experts dietitian Dr Emily Leeming and nutritional psychologist Kimberley Wilson, who shared the theory during this year’s Cheltenham Science Festival.
Dementia, a neurodegenerative disease which causes memory loss, is “a model of accelerated brain ageing – it’s as if you turned the dial up on ageing,” Wilson said.
“That’s why this is relevant to everybody – not just people who think they may have a risk factor for Alzheimer’s. Everyone who cares about keeping their brain sharp should be thinking about these things.”
According to Leeming and Wilson, a fibre deficiency – something that most adults suffer from – is one such risk factor.
Yet most people in the UK are fibre deficient. “We need at least 30g of fibre a day for good health,” Leeming told BBC Science Focus. But UK adults are only getting around 19g a day, while US adults are consuming as little as 15g.
“There are a number of factors likely behind why we aren’t getting enough fibre into our diets,” Leeming said.
“The 2023 Broken Plate report [by charity The Food Foundation] found that healthy foods, like fibre-rich fruits and vegetables, are twice the price of less healthy (and low-fibre) foods like ultra-processed foods, with ultra-processed foods making up 60 per cent of the UK diet.”
How does fibre protect the brain?
Wilson called fibre “one of the underappreciated protectors of the brain”. When you feed your gut microbes fibre, one of the byproducts when they metabolise it is short-chain fatty acids.
These support the lining of the gut, but they can also cross into your bloodstream and travel to your brain. Here, they are one of the few things that can get through your blood-brain barrier (BBB): the very selective structure that controls what goes into your brain like a “bouncer outside the nightclub,” according to Wilson.
Short-chain fatty acids protect the junctions within the BBB to stop anything toxic getting through. “One of my questions is: are we losing some of the protective benefits from fatty acids on the blood-brain barrier because our diets are so deficient in fibre? People don’t tend to make that link,” Wilson said.
What can we do if we are fibre deficient?
According to Leeming, fibre is essential to the health of your gut. It “sweeps away any build-up” and helps you feel fuller and more satisfied. It has also been shown to help with managing your blood sugar levels and blood pressure. Plus, the fatty acids that support your brain health also fight inflammation.
To improve your fibre levels, Leeming’s top tips are:
- Focus on adding fibre-rich foods like rye bread and beans into your diet.
- Snack on a handful of nuts a day, or add a mix of nuts and seeds to your breakfast.
- Make half your plate veggies.
- If you’re looking for something sweet, 85 per cent dark chocolate is surprisingly high in fibre, containing about 11g/100g.
- Keep the skin on potatoes and root veggies like carrots and parsnips, for an extra boost.
"Eating more fibre is not only linked to lower risk of colorectal cancer, type II diabetes and heart disease, but it can also help you feel healthier and more energised today," Leeming said. "It also feeds your gut microbiome, which is involved in every aspect of your health.”
About our experts
Kimberley Wilson is a Chartered Psychologist, with a master’s degree in nutrition and the author of How to Build a Healthy Brain and Unprocessed: How the Food We Eat is Fuelling our Mental Health Crisis.
Dr Emily Leeming is a Registered Dietitian and research fellow at King's College London. She holds a BSc in Nutrition, MSc in Nutrition and Dietetics, and a PhD in the impact of diet on the gut microbiome. Her new book is called Genius Gut: The Life-Changing Science of Eating for Your Second Brain.