Dietary Intervention Shows NeuroprotectionBy Rosalie Marion Bliss
March 31, 2009
Adding a moderate, but not high, amount of walnuts to an otherwise healthy diet may help older individuals improve performance on tasks that require motor and behavioral skills, according to an animal model study by Agricultural Research Service (ARS)-funded scientists. Walnuts contain polyphenols and other antioxidants and essential fatty acids.
The study was conducted by researchers with the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts University in Boston, Mass.
Neuroscientist James Joseph, psychologist Barbara Shukitt-Hale and coauthors Lauren Willis and Vivian Cheng reported the study in the British Journal of Nutrition. They are with the HNRCA's Neuroscience Laboratory. ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.
The aging brain undergoes many changes that can result in altered or impaired neuronal functioning. Such disruption can be attributed in part to alterations in "synaptic plasticity," or the ability of the connections between neurons to change in strength and function, and also by increased oxidative damage to neural tissue. In aged rodents, these impairments are seen as poor performance on age-sensitive tests of balance, coordination, and "spatial" working memory.
For the study, weight-matched, aged rats were randomly assigned to one of four diet groups. For eight weeks, the rats were fed special chow mixes that contained either 2 percent, 6 percent or 9 percent walnuts-or no walnuts-before undergoing motor and memory tests. For comparison, the 6 percent walnut study diet is equivalent to a human eating 1 ounce, or about 7 to 9 walnuts, a day. That counts as both a 2-ounce equivalent from the "meat and beans group" and 2 teaspoons toward a daily allowance of dietary oil, as described at MyPyramid.gov.
The study found that in aged rats, the diets containing 2 percent or 6 percent walnuts were able to improve age-related motor and cognitive shortfalls, while the 9 percent walnut diet impaired reference memory. Walnuts, eaten in moderation, appear to be among other foods containing polyphenols and bioactive substances that exhibit multiple effects on neural tissue, according to the researchers.