Junkfood Science: Keeping smart about fruits and vegetables

November 29, 2006

Keeping smart about fruits and vegetables

Mom was right about those veggies: Vegetables can help fend off age-related memory loss

Study: Vegetables May Keep Brains Young

Oh really?

The news tell us that eating our veggies can keep us sharp as we grow older but is there any evidence for that claim?

Fruits and vegetables are certainly a welcome part of all the foods we enjoy. While we want to believe that these brightly colored, crunchy treats also have special anti-aging benefits, the evidence is remarkably fuzzy. The study being reported in these news stories is a prime example of the findings of a weak study being greatly exaggerated — by both the media and scientists.

Lead researcher, Martha Clare Morris, chief of Rush University Medical Center’s Rush Center for Healthy Aging in Chicago, told reporters that the slowdown in cognitive decline among those who ate 2.8 or more servings of vegetables a day was “equivalent to about five years of younger age.”

The conclusion in the published study was considerably more conservative, and rightly so: “High vegetable but not fruit consumption may be associated with slower rate of cognitive decline with older age.”

This study was not a clinical intervention trial, carefully designed, randomized and controlled to demonstrate that fruits and vegetables were actually the reason for any differences in cognitive function among elderly people. It was looking for associations among a certain population.

At the beginning of the study, food frequency questionnaires were gathered from 3,718 retirees who were part of the Chicago Health and Aging Project. Their cognitive functions were then tested using fairly crude measures involving word recall, mini-mental state evaluations, etc. The researchers put all of this into their computers looking for associations between cognitive changes over six years and how often the older people ate fruits and vegetables. [Remember, food frequency questionnaires don’t measure how much people eat of various foods, just how many times they remember eating them.]

They found an association between less of a decline in cognitive function and a greater number of vegetable servings eaten. Compared to those eating only about one serving a day, there was a 40% lower decline among those eating almost 3 servings a day and 38% among those eating the greatest number of servings (4.1 servings). While expressed as relative risks those percentages sound impressive. But as we know, such numbers are untenable for these types of studies. And the actual differences on the cognitive test scores really bring home just how untenable those percentages are: a 0.019 standard unit difference and a 0.018 standard unit difference, respectively. Numbers so tiny that their ability to predict real-life differences is questionable, at best. In another universe, this would be considered a non-finding.

The researchers also didn’t factor for things well-known to affect mental function among the elderly, such as their living situations and degree of isolation, social support, degree of stimulation and interactions with people, depression, etc. They also didn’t consider activity levels, another indication of general physical and mental health.

Since it is popularly believed that antioxidant nutrients confer such anti-aging benefits, it is curious that the researchers couldn’t convincingly explain why they were unable to find any correlation with the number of servings of fruits eaten!

The take home message is usually to turn the page or change the channel when a study report uses words like association, link, correlation, or related. Except studies aren’t always reported accurately. Look closely at those headlines and news stories. They make several leaps of faith, based on no credible evidence:

1. vegies are associated with less mental decline

2. lack of vegies are the cause for reduced mental sharpness

3. eating more vegies can prevent a decline in mental function

Just because something sounds intuitively correct, doesn’t always make it so. And correlations can never show causation. Rolls-Royce owners enjoy greater general health, but buying a Rolls-Royce is certainly not going to make you healthier. Although you may feel better. :)

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