A Mediterranean-style diet that is rich in oily fish, fresh vegetables and nuts could help cut the risk of dementia, research suggests.
New studies presented at the Alzheimer's Association International Conference in London examined links between diet and dementia and found that following a nutrient-rich diet helps keep the brain healthy.
In a study on almost 6,000 people, led by the University of California at San Francisco, scientists found that those who stuck the closest to a Mediterranean or similar diet over the course of a year were 30% to 35% less likely to have low scores on cognitive tests than those who did not stick to such a diet.
This was even after taking into account factors such as smoking, exercise, overall health and socio-economic status.
Claire McEvoy, co-author of the research, said the benefits of healthy eating seem to exist on a sliding scale.
"Even moderate adherence to these high-quality dietary patterns showed a protective association with cognitive function," she said.
Dr Maria Carrillo, chief science officer for the Alzheimer's Association, said the study showed that changing your dietary pattern "really is quite impactful".
She told Fox Business: "You can change your trajectory of cognitive decline if you are adherent, for example, to Mediterranean diets or other diets that are low in saturated fats, low in processed flour and processed sugar.
"Good fats are important. Fats found in fish and good meats, as opposed to red meats, are all very good for your brain."
She said another study from Columbia University had shown that poor nutrition may increase inflammation in the body and lead to brain shrinkage.
She said: "People that perhaps eat a lot of junk food and processed foods may end up having less brain cognition over time as they age and may actually have smaller brains."
A Mediterranean diet includes vegetables, fruit, nuts, seeds, fish, olive oil and whole grains, while being low in red and processed meat, and with alcohol kept to a minimum.
People who are considered to get maximum benefit from the diet have less than one alcoholic drink a day for women, or one to two for men.
They also eat several servings of fruit and vegetables per day, one serving of wholegrains and up to four servings of fish per week.
Another study on more than 2,200 older adults, from the Karolinska Institute in Sweden, found that people who stuck to a Nordic diet that consists of non-root vegetables, fruit, fish and poultry enjoyed a better cognitive status than those who ate a less healthy diet.
And another study on more than 7,000 people in the US found that older women who ate diets traditionally thought of as heart-healthy, such as a Mediterranean diet, were less likely to develop dementia.
Keith Fargo, the Alzheimer's Association's director of scientific programmes and outreach, said: "Although the idea that a healthy diet can help protect against cognitive decline as we age is not new, the size and length of these four studies demonstrate how powerful good dietary practices may be in maintaining brain health and function.
"That said, we must understand that what we eat is just one part of the puzzle.
"Adapting our lifestyles as we get older, for example by exercising regularly, watching what we eat and engaging in lifelong learning, is important in order to maximise the potential to reduce risk of cognitive decline and dementia."
Dr Doug Brown, director of research and development at the Alzheimer's Society, said: "These studies continue to build on the increasing evidence that suggests a Mediterranean-style diet that's rich in oily fish, fresh vegetables and nuts can help to maintain your memory as you get older, as well as maintaining your heart's health.
"We're starting to see evidence that this diet can not only help maintain memory, but also reduce the risk of dementia."
Another study from the University of Wisconsin found that people who experience hearing loss could have more problems with memory and thinking in later life than those with normal hearing.
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