We're told repeatedly to eat more fruit and vegetables – they're packed with fibre, vitamins A and C, folate and hundreds of antioxidants including beta-carotene, lutein and lycopene.
What's more, a diet plentiful in fruit and vegetables has been linked to a lower risk of heart attack, stroke, high blood pressure, macular degeneration, even certain cancers.
Now, new study findings suggest there's another reason to boost your intake: Eating more fruit and vegetables – especially fruit – can protect your memory as you age.
Age-related cognitive decline – the subtle decrease in memory and thinking processes – is considered to be a normal consequence of getting older. (In some people, cognitive decline can progress to mild cognitive impairment, a risk factor for Alzheimer's disease.)
Previous research has linked certain diet factors – berries, spinach, fish, fruit and vegetables – with better cognitive performance.
Yet data on specific types of fruit and vegetables have been inconsistent, leading researchers to speculate that certain foods and nutrients act on different parts of the brain and affect cognition in unique ways.
The current study, published online in the American Journal of Clinical Nutrition, involved 2,533 healthy men and women, aged 45 to 60. Intakes of fruits, vegetables and specific nutrients were measured to determine associations with cognitive function.
Participants were followed for 13 years at which time they took tests to measure two components of cognition: verbal memory (the memory of words and their meaning) and executive function (mental processes involved in planning, problem solving and multi-tasking). It's verbal memory that's especially vulnerable to the effects of aging and Alzheimer's disease.
People with a higher daily consumption of fruit and vegetables (total servings combined) performed better on verbal memory tests than their peers who consumed less. So did individuals with a higher daily fruit intake and those who consumed more vitamin C-rich fruit and vegetables (combined).
High consumers ate, on average, eight daily servings of fruit and vegetables combined. Three of these servings consisted of vitamin-C rich produce and 4.4 of total servings consisted of fruit.
When the researchers looked at vegetables separately, they found no relationship between a high intake and memory. This suggests the association between high consumption fruit and vegetables and verbal memory is attributed to fruit.
A higher intake of vitamins C and E – from foods, not supplements – was also linked with better verbal memory. Vitamins C and E act as antioxidants, protecting brain cells from damage caused by free radicals.
Fruit intake had no effect on cognitive tests that measured planning, problem solving and multi-tasking skills. However, vegetable intake was linked with poorer performance. It's possible that pesticide residues in vegetables may increase the risk of cognitive impairment.
Keep in mind, however, this negative association was found only with one test, which was administered first. Test order can impact the results of cognitive testing; beginning psychological testing can induce anxiety.
According to these findings, fruit has a stronger impact on mental prowess than vegetables. It's possible that antioxidants are better preserved in fruit than vegetables, which are often cooked.
Even so, that's no reason to downplay vegetables in your diet. Green leafy vegetables such as kale, arugula, Swiss chard, collard greens, rapini and spinach – sources of vitamin E – have previously been shown to guard against cognitive decline. They're also excellent sources of lutein, an antioxidant that helps preserve vision as we age.
Based on evidence to date, the following foods and nutrients can help safeguard your thinking power as you age.
Fruit and vegetables
Aim for seven to 10 servings of fruit and vegetables (combined) each day. One serving is equivalent to a medium-sized fruit, ¼ cup dried fruit, ½ cup of cooked or raw vegetables, one cup of salad or ½ cup of 100-per-cent vegetable or fruit juice.
Make a plan to include these foods in all meals and snacks. And don't discount frozen produce. Frozen fruit and vegetables rival or outshine fresh as a source of vitamins and minerals. That's because processing and packaging takes place almost immediately after harvest, locking in more nutrients.
Vitamin C-rich produce
This antioxidant protects brain tissues from oxidative damage and inflammation, processes thought to increase the risk of cognitive impairment and Alzheimer's disease.
Aim to include at least three servings of fruit and vegetables high in vitamin C in your daily diet. Top fruits for vitamin C include cantaloupe, grapefruit, kiwi, mango, oranges, papaya, pineapple and strawberries.
Vitamin C-rich vegetables include broccoli, Brussels sprouts, cabbage, cauliflower, green and red peppers, kale and tomato juice.
Vitamin E-rich foods
This nutrient helps shield brain cell membranes from harmful free radicals. It's also thought to lessen the toxic effects of beta-amyloid, a sticky protein linked to Alzheimer's.
The best sources of vitamin E include wheat germ oil, sunflower seeds, sunflower oil, safflower oil, grape-seed oil, almonds, hazelnuts, mixed nuts, frozen spinach, beet greens, canola oil and papaya.
Berries and walnuts
These foods contain polyphenols, phytochemicals that protect brain cells by fighting free radical damage, reducing inflammation and increasing the clearance of toxic proteins that accumulate with age.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.