How a healthy diet can lower the risk of dementia

Everyone knows that adopting a healthy diet and lifestyle can help prevent common diseases, but it also plays a big part in the risk of developing dementia.

According to the World Health Organisation, more than 55 million people worldwide live with dementia, with nearly 10 million new cases every year. Dementia is driven by the same mechanisms as other chronic conditions, namely inflammation, dyslipidaemia, oxidative stress, insulin resistance and an unhealthy gut microbiome.

Therefore, adopting healthy diet and lifestyle habits can help to address these key risk factors and help to prevent or delay dementia⁽¹⁾.

What is a healthy diet?

In general, diet patterns centred around healthy plant foods, whilst being low or avoiding animal-derived and processed foods, are best for preventing chronic diseases, including dementia⁽²⁾.

This includes diet patterns such as the Mediterranean, dietary approach to stop hypertension (DASH) and Mediterranean-DASH diet intervention for neurodegenerative delay (MIND) and a fully plant-based diet⁽²⁾.

Diets high in animal and processed foods, and low in plant foods, increase inflammation and oxidative stress, promote lipid and glucose dysregulation and result in insulin resistance.

In contrast, healthy plant-based diets have been associated with lower levels of inflammation and are packed full of antioxidant compounds that help counteract different types of cellular stress, whilst promoting insulin sensitivity and a healthy gut microbiome.

Which foods are best to avoid or reduce?

Higher intake of saturated fat is associated with an increased risk of dementia⁽⁸⁾. Saturated fat in the diet comes predominantly from animal foods, and the consumption of processed red meat seems to be particularly bad for brain health⁽³⁾.

Diets high in refined sugars and carbohydrates also appear to impair cognitive function, both in the short⁽⁴⁾ and long term⁽⁵⁾, the latter in part due to the ability of sugar to increase inflammation and the risk of cardiovascular disease.

Interestingly even artificially-sweetened beverages, in some but not all studies, have been associated with an increased risk of dementia⁽⁶⁾.

Which foods can help prevent dementia?

The best foods for brain health are the brightly coloured fruit and vegetables⁽⁷⁾. Vegetables, particularly the green leafy varieties, appear more important than fruit in protecting against dementia, with the exception of berry consumption, which appears highly protective against cognitive decline⁽⁸⁾.

A recent study highlighted the importance of eating fruit and vegetables early in life to prevent later cognitive impairment⁽⁹⁾. This study recruited more than 3,000 participants in the United States aged 18-30 years, in the 1980’s, and followed them for 25 years, regularly documenting their dietary intake.

The research found that those consuming the most fruit and vegetables in younger age had the best cognitive function later in life. Vegetable consumption had a greater effect than fruit, with nutrients such as lycopene from tomatoes/red vegetables and beta-carotene from yellow/orange vegetables having the best effect.

Overall, it seemed that it was the fibre intake that was responsible for much of this beneficial effect on brain health. Fibre intake is correlated with lower risk of many chronic diseases that increase the risk of dementia, such as type 2 diabetes and high blood lipids. Fibre also benefits gut bacteria, which then can make short-chain fatty acids needed for brain hormone production and for reducing inflammation.

Eating fruit and vegetables that are high in flavonoids may be of particular benefit. Flavonoids are a class of polyphenols representing more than 5,000 bioactive compounds that are found in a variety of fruit and vegetables, including grapes, berries, apples and in tea. Several studies have reported a beneficial effect of flavonoids for preventing cognitive decline, reducing the risk by around 20%⁽¹⁰⁾.

Furthermore, an analysis of the prospective three-city cohort study in Europe, including 842 participants with a median age of around 75 years and followed for 12 years, showed that a higher intake of fruit, vegetables and plant-based foods providing polyphenols and other bioactive compounds was associated with the generation of beneficial compounds from the gut microbiota⁽¹¹⁾. These gut-derived compounds detected in the blood were associated with a reduced risk of cognitive decline.

Higher intakes of carotenoids from yellow/orange vegetables and dark leafy greens have also been found to protect brain health. A study that followed 927 elderly US residents for seven years found that those consuming the most carotenoid-rich foods had a 48% reduction in the risk of developing dementia⁽¹²⁾.

DHA (long chain omega-3 fatty acid) is very important for the developing brain and has also been shown to be important in protecting the aging brain. The brain is composed of around 50-60% fat and has a particularly high content of DHA. Regular consumption of fish appears to reduce the risk of dementia and it is thought that this is due to the high DHA content in fish⁽¹³⁾.

Interestingly, supplementation with DHA does not seem to consistently reduce the risk of dementia, so it may be that fish consumption is a reflection of a healthier diet where fish is replacing harmful foods such as processed and unprocessed red meat⁽¹⁴⁾.

Those on a plant-based diet will be mainly consuming short-chain omega-3 fatty acids from nuts and seeds, which is then converted to DHA. There is currently no evidence to suggest a lack of fish in the diet is detrimental for brain health when the diet is otherwise composed of healthy, minimally processed plant foods⁽¹⁵⁾. Long-chain omega-3 fatty acids can be obtained from algae supplements if required.

In addition, recent evidence suggests that vegetarians may have a reduced risk of developing dementia compared to non-vegetarians, suggesting that fish is not required for optimal brain health⁽¹⁶⁾.

International recommendations for a brain-healthy diet

In 2019, the World Health Organisation published guidelines for the prevention of dementia.

For a healthy diet, the following recommendation were made⁽¹⁷⁾:

• Eat a diet rich in fruit, vegetables, legumes (e.g. lentils and beans), nuts and whole grains (e.g. unprocessed maize, millet, oats, wheat and brown rice).
• Eat at least 400g (i.e. five portions) of fruit and vegetables per day
• Consume less than 10% of total energy from sugars, which is equivalent to 50g (or about 12 level teaspoons) for a person of healthy body weight consuming about 2,000 calories per day.
• Consume less than 30% of total energy intake from fats, choosing unsaturated fats, rather than saturated fats, and industrialised trans-fats (found in baked and fried foods, and pre-packaged snacks and foods, such as frozen pizza, pies, cookies, biscuits, wafers, and cooking oils and spreads) and ruminant trans-fats (found in meat and dairy foods from ruminant animals, such as cows, sheep, goats and camels). Keep saturated fat intake to less than 10% of total energy intake
• Eat less than 5g of salt (equivalent to about one teaspoon) per day.

Conclusions

We have enough evidence to support the important role of a healthy plant-based diet, alongside other health lifestyle habits for promoting brain health and preventing dementia. Lifestyle interventions not only reduce the risk of common chronic health conditions known to increase the risk of dementia, but also address the underlying pathogenic mechanisms at play in the development of dementia.

For more information on other lifestyle risk factors that can affect dementia, please click here.

About the author 

Dr Laura Freeman is a GP and lifestyle medicine physician. She is co-founder of Plant Based Health Online, an online lifestyle medicine healthcare service that supports patients to adopt healthy lifestyle habits for prevention and treatment of chronic illness.

You can find out more about Dr Freeman here or by visiting www.pbho.co.uk

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