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Fruits and vegetables have been the focus of many studies investigating the role of diet in cognitive function. Yet research has turned up inconsistent results, likely due to small sample sizes and study durations that were too short to find a protective effect.

Now, a large study spanning two decades has linked eating plenty of fruits and vegetables from middle to late adulthood to significant protection from memory loss. And certain fruits and vegetables were found to be especially protective.

The study, published last month in the journal Neurology, followed 27,842 male health professionals (dentists, optometrists, pharmacists, podiatrists and veterinarians) for 18 to 22 years. The researchers tracked participants’ diets every four years and assessed their subjective cognitive function (SCF) twice during the study.

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SCF – scored good, moderate or poor – is assessed using a self-reported questionnaire that measures changes in memory and cognition. It’s thought to capture the earliest signs of cognitive decline.

The findings

Total vegetable intake (more than five daily servings versus less than two), total fruit intake (three daily servings versus 0.5) and fruit juice intake (daily consumption versus less than once a month) were each associated with a significantly lower risk of moderate and poor SCF.

The link became even stronger after accounting for other risk factors such as body weight, physical activity, heavy smoking, high blood pressure, high cholesterol and depression.

When researchers looked at specific categories of produce they found that leafy green vegetables (e.g. spinach, kale, lettuce) and berries provided significant protection against cognitive decline.

Tomatoes (especially tomato sauce), brussels sprouts, bell peppers and cantaloupe were also tied to a lower risk of moderate and poor SCF.

The protective effect of fruit juice was attributed to orange juice; participants who drank it daily were 47 per cent less likely to have a poor SCF score than those who drank orange juice less than once a month.

It’s thought that antioxidant nutrients and other phytochemicals in vegetables and fruit help keep your brain healthy as you age. Leafy green vegetables, tomatoes and orange juice, for instance, are excellent sources of carotenoids, compounds that help shield brain cells from free-radical damage.

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Berries are packed with polyphenols, phytochemicals that fight harmful free radicals and dampen inflammation. Polyphenols have also been shown to remove toxins that can interfere with brain function.

Strengths and limitations

Unlike previous studies, the large sample size and more than 20 years of follow-up provided insight into the relationship between long-term intake of fruits and vegetables and later-life cognitive function.

The research was observational, though, and doesn’t prove cause and effect. Since the study was conducted in men, the findings may not apply to women.

As well, the self-reported questionnaire used to assess cognitive function could be prone to error. (However, growing evidence has identified subjective cognitive function as a precursor to mild cognitive impairment, a risk factor for Alzheimer’s disease.)

Even so, this new study lends supports to earlier findings.

In 2015, researchers from Rush University Medical Center in Chicago tied a dietary pattern called the MIND diet, rich in leafy greens and berries as well as other brain-friendly foods, to a slower rate of cognitive decline and lower risk of Alzheimer’s disease. (MIND stands for Mediterranean-DASH Intervention for Neurodegenerative Delay.)

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What to eat for brain health

Research suggests that the following foods can help maintain brain health as you age:

Leafy greens. Include these nutrient powerhouses – e.g., spinach, kale, Swiss chard, collards, rapini, arugula – in your diet at least six times a week. Besides eating salad, add leafy greens to soup, chili, pasta sauce and smoothies.

Berries. Eat berries – e.g., blueberries, blackberries, strawberries, raspberries – at least twice a week. Other polyphenol-packed fruits include acai berries, cherries, cranberries and pomegranate seeds. Blend berries into smoothies and protein shakes, toss them into leafy green salads and add them to oatmeal, pilafs and muffin and pancake batters.

Nuts. Eating nuts (all types) helps lower elevated blood pressure and LDL (bad) cholesterol and guards against Type 2 diabetes, risk factors for memory loss and Alzheimer’s disease. They’re also good sources of vitamin E, an antioxidant nutrient linked to a slower rate of cognitive decline. Include a small handful (one-quarter cup) in your diet at least five times per week.

Pulses. Kidney beans, black beans, chickpeas and lentils are packed with brain-friendly nutrients including folate and low-glycemic carbohydrates. Eating more pulses can also help lower blood pressure and cholesterol.

Fish. Oily fish such as salmon, trout, sardines and herring are plentiful in DHA, an omega-3 fatty acid essential for brain function. Eat fish twice a week.

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Olive oil. A rich source of monounsaturated fat, the type that helps reduce inflammation, extra-virgin olive oil also contains phytochemicals thought to remove beta-amyloid from the brain, a protein that can interfere with communication between brain cells.

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan.

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