ONE of the most rigorous randomised controlled studies ever done on the effect of a diet on cognitive performance was conducted in Spain in 2015, and the results were published in the journal JAMA Internal Medicine.
The study investigated whether a Mediterranean diet supplemented with antioxidant-rich foods influences cognitive function compared to a low-fat diet.
The randomised clinical trial comprised 447 cognitively healthy volunteers from Barcelona, Spain, with a median age of 66.9. They were enrolled in the Prevención con Dieta Mediterránea nutrition intervention trial from October 1, 2003, to December 31, 2009. All patients underwent neuropsychological assessment at induction and were offered retesting at the end of the study.
It was part of a more extensive five-year investigation called PREDIMED of the effects of diet on cardiovascular health. Participants were randomly assigned to eat one of the following:
A Mediterranean diet supplemented with 33 ounces (935 g) a week of extra-virgin olive oil;
A Mediterranean diet supplemented with an ounce a day of mixed nuts;
A controlled low-fat diet.
The conclusion was that in an older population, a Mediterranean diet supplemented with olive oil or nuts was associated with improved composite measures of cognitive function. The authors speculate that the benefits to cognition likely come from the antioxidant and anti-inflammatory effects of foods like olive oil and nuts: “Oxidative stress and vascular impairment are believed to partly mediate age-related cognitive decline, a strong risk factor for the development of dementia."
In 2022, a further study of 6321 Hispanic or Latino adults, also published in JAMA, found that “high adherence to a Mediterranean diet was associated with better cognitive performance and decreased 7-year learning and memory decline among middle-aged and older Hispanic or Latino adults. A culturally tailored Mediterranean diet may reduce the risk of cognitive decline and Alzheimer's disease in this population."
Interest in the so-called Mediterranean diet began in the 1950s when it was noted that people in Spain, Greece, Italy and other countries bordering the Mediterranean Sea had much lower rates of heart disease and tended to live longer than their counterparts in the U.S.
According to the Mayo Clinic, the foundation of the diet is plant-based foods, such as whole grains, vegetables, legumes, fruits, nuts, seeds, herbs and spices. Fish, seafood, dairy and poultry are included in moderation. Red meat and sweets are eaten only occasionally.
Olive oil is the primary source of added fat in the Mediterranean diet. Olive oil provides monounsaturated fat, which research has shown helps lower total cholesterol and low-density lipoprotein (or “bad") cholesterol levels. Nuts and seeds also contain monounsaturated fat.
Fatty fish, such as mackerel, herring, sardines, albacore tuna and salmon, are rich in omega-3 fatty acids. These poly-unsaturated fats help fight inflammation, and omega-3 fatty acids also help decrease triglycerides, reduce blood clotting, and lower the risk of stroke and heart failure.
What we know
There is no “special brain food", but there is compelling research to indicate incorporating certain foods into your diet, and cutting out others, can help to protect your heart and blood vessels — and support cognitive fitness, especially in older people.
This article from Harvard Medical School supports this view.
“The range of foods you choose from day to day can have an enormous impact not only on your weight, heart health, and cancer risk, but also on your mood, your mental sharpness, and your risk of developing dementia.
“Nutritionists emphasise that the most important strategy is to follow a healthy dietary pattern that includes a lot of fruits, vegetables, legumes, and whole grains. Protein should come from lean sources, such as fish, and fats should be healthy, such as olive or canola oil."
Canola oil is generally considered a “healthy" oil because it is very low in saturated fat (7%) and, like olive oil, is high in mono-unsaturated fat (63%) and contains a significant level of poly-unsaturated omega-3.
Specific food groups
The Harvard article (“Foods linked to better brainpower") identifies some food groups that other studies have also shown to support the heart/brain benefits (hint: they fall very much within the remit of the Mediterranean Diet).
Green, leafy vegetables
Leafy greens like kale, spinach, collards, and broccoli are rich in brain-healthy nutrients like vitamin K, lutein, folate, and beta-carotene.
Fatty fish contains omega-3 fatty acids, healthy unsaturated fats that have been linked to lower blood levels of beta-amyloid. This protein forms damaging clumps in the brains of people with Alzheimer's disease. Try to eat fish at least twice a week but choose varieties low in mercury (canned sardines or light tuna are a good option). Flaxseeds, avocados, and walnuts are also high in omega-3.
There is evidence that flavonoids, the natural plant pigments that give berries their brilliant colour, can help to improve memory.
This 2012 study was conducted by researchers at Harvard's Brigham and Women's Hospital and published in the Annals of Neurology journal. They investigated the relationship between the consumption of strawberries and blueberries and memory decline in women.
The study's findings suggested that women who consumed two or more servings of strawberries and blueberries per week experienced a delay in memory decline by up to two-and-a-half years compared to those who did not consume these fruits regularly. The researchers observed a potential protective effect of these berries on cognitive ageing and memory function in women.
Tea and coffee
Researchers at Johns Hopkins University have found that caffeine can be a memory enhancer.
After studying a series of images, participants who were given 200-milligram caffeine tablets were better at distinguishing these images from similar ones when tested the next day.
According to the senior author of the study, Michael Yassa, an assistant professor of psychological and brain sciences at the university, “We've always known that caffeine has cognitive-enhancing effects, but its particular effects on strengthening memories and making them resistant to forgetting has never been examined in detail in humans."
The double-blind study was designed to reveal a deeper interaction between memory and caffeine. In earlier studies where they used a standard recognition memory task, they did not see any effect of caffeine. Still, when they required the brain to make more difficult discrimination — what the study calls “pattern separation" — they found that caffeine did enhance brain function.
Their research, published in the journal Nature Neuroscience, shows that caffeine enhances specific memories at least up to 24 hours after it is consumed.
Walnuts. Nuts are excellent sources of protein and healthy fats; one type of nut, in particular, has been shown to improve memory.
This 2015 study from UCLA linked higher walnut consumption to improved cognitive test scores. Walnuts are high in a type of omega-3 fatty acid called alpha-linolenic acid (ALA), which helps lower blood pressure and protects arteries. So once again, what's good for the heart is good for the brain.
Tips to be ‘more Mediterranean’
Best Cognitive Diets, a booklet published by Harvard Medical School, outlines a range of tips for adopting a brain-and-heart-supporting Mediterranean-style eating plan:
- Replace red meat with fish — especially salmon, pollock, catfish, and canned light tuna, which are high in omega-3 fatty acids but low in mercury — at least twice a week.
- Cook with unsaturated fat like olive oil instead of butter, which is mainly saturated fat.
- Fill half of your plate with fruits or vegetables — the more colourful the produce you choose, the more antioxidants and nutrients you’ll consume. Berries, carrots, broccoli, red peppers, oranges, and spinach are all good choices.
- Drink wine (in moderation). A little red wine is good for blood vessels, but moderation is key.
- Make your grains whole grains. Check the labels to ensure the pasta, bread, and cereals you buy contain 100% whole grain. Oats, quinoa, barley, and rye are some of the healthiest whole grains.
- Grab a handful of nuts. Walnuts, almonds, and other varieties make great snacks because they’re packed with protein that fills you up, plus unsaturated fat.
- Have fruit for dessert. A bowl of berries will give your meals a sweet finale without adding a lot of fat and calories whilst adding antioxidants.
Dr Martha Clare Morris and colleagues at Rush University Medical Center and the Harvard Chan School of Public Health developed the so-called MIND diet (Mediterranean-DASH Diet Intervention for Neurodegenerative Delay) based on research they had done where they followed more than 1,000 older adults for up to 10 years. The participants were recruited from more than 40 retirement communities and senior public housing units in the Chicago area. They were free of dementia at the time they entered the study programme. The participants completed nine-year annual dietary questionnaires and had two cognitive assessments.
A MIND diet score was developed to identify foods and nutrients and daily serving sizes related to protection against dementia and cognitive decline. The study's results produced 15 dietary components classified as either “brain healthy" or unhealthy. Participants with the highest MIND diet scores had a significantly slower rate of cognitive decline than those with the lowest scores.
The MIND diet recommends specific “brain-healthy" foods to include and five unhealthy food items to limit. The healthy list has all the Mediterranean favourites, foods rich in vitamins, carotenoids, and flavonoids that are now believed to protect the brain by reducing oxidative stress and inflammation.
The unhealthy list includes:
- Less than five servings a week of pastries and sweets
- Less than four servings a week of red meat (including beef, pork, lamb, and products made from these meats)
- Less than one serving a week of cheese and fried foods
- Less than one tablespoon day of butter
Morris's research is astonishing.
Those with the highest MIND scores had a 53% lower rate of Alzheimer's disease. And even for participants with moderate MIND scores, there was a 35% lower rate of Alzheimer's compared to those with the lowest MIND scores.
These results didn't change even after adjusting for factors associated with dementia, like lifestyle behaviours, cardiovascular-related conditions (e.g. high blood pressure, stroke, diabetes), depression, and obesity.)
This supports the conclusion that what we eat and exclude from our diet can significantly impact our cognitive fitness.
So, while there might not be specific “brain foods," there most certainly is a give-your-brain-a-better-chance diet.
♦ VWB ♦
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