Eating almonds significantly decreased levels of two biomarkers for oxidative stress in a group of 27 male and female volunteers with elevated cholesterol. The study was conducted by scientists funded by the Agricultural Research Service, the Almond Board of California, and the Canada Research Chair Endowment.

Coauthor Jeffrey Blumberg is director of the Antioxidants Research Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts University in Boston, Mass. He and colleagues reported the findings from this study in the Journal of Nutrition.

HNRCA scientists analyzed blood and urine samples from the subjects who had consumed three different dietary treatments, consisting of the same amount of calories each, for one month. The study was a cross-over, randomized clinical trial, so each subject received each treatment in random order.

Treatments consisted of a "full dose" of almonds, defined as 73 grams daily (about 2.5 ounces), a "half-dose" of almonds plus a half-dose of muffins, and a full-dose of muffins as a control. The subjects consumed a low-fat background diet and were counseled on strategies to maintain weight and to consistently follow their usual exercise routines throughout each test phase.

The researchers wanted to investigate possible antioxidant effects from eating almonds.

The team found that when the volunteers ate the full dose of almonds, their concentration of two biomarkers of oxidative stress — plasma malondialdehyde (MDA) and urinary isoprostanes — were significantly lowered. MDA decreased by nearly 19 percent compared to the start of the study in the full-dose almond group. Isoprostane decreased by 27 percent in both the almond groups when compared to the control period, suggesting a possible threshold effect for that biomarker.

While this study helps to show the antioxidant benefit of eating almonds, further research is needed to shed light on the individual contributions of vitamin E and polyphenolic constituents, such as flavonoids, found in almonds and other tree nuts. The study did not demonstrate a minimum amount of dietary almonds that would result in a biological effect.