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Bagel sandwich with salmon
Salmon, often eaten with bagels, contains a healthful omega-3 fatty acid known as DHA, short for docosahexaenoic acid.

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Secrets of Fish Oil Compound Probed

By Marcia Wood
December 3, 2007

A compound found in oil-rich fish such as salmon reshaped the blood lipid profiles of volunteers in an Agricultural Research Service-led study.

Research chemist Darshan S. Kelley of the ARS Western Human Nutrition Research Center in Davis, Calif., and federal and university co-investigators conducted the study of DHA, or docosahexaenoic acid, a polyunsaturated fatty acid thought to improve cardiovascular health.

The research, reported earlier this year in the American Journal of Clinical Nutrition, is likely the first to analyze—in high-triglyceride males—DHA's effects on both fasting and post-meal triglycerides, and on quantities and sizes of HDL, LDL and VLDL cholesterol particles. High triglycerides, high cholesterol and a high number of small particles of LDL cholesterol in the blood increase risk of cardiovascular disease, the nation's leading cause of death, according to Kelley.

The study is also one of only about a dozen, in humans, to probe the effects of DHA alone, rather than in tandem with another natural oil, EPA, or eicosapentanoic acid. EPA occurs with DHA in fish oil.

Half of the study’s 34 volunteers, age 39 to 66, consumed about one-half teaspoon of DHA daily, in addition to regular meals, for 90 days. The other half received olive oil in place of DHA oil.

Blood samples taken after fasting, and within eight hours after meals, showed that DHA reduced by 22 percent the number of small LDL (low-density lipoprotein) particles. LDL’s small particles are the size most harmful to the cardiovascular system. DHA increased the number of large LDL particles by 127 percent. Since large LDL particles are less harmful than small ones, some researchers believe large LDL particles do not harm the arteries.

DHA also lowered triglycerides by 24 percent in both the fasting and post-meal samples. The after-meal effect, shown in only a few other studies, may be of particular interest to medical professionals looking for alternatives to conventional triglyceride-lowering therapies, according to Kelley.

ARS is the U.S. Department of Agriculture's chief scientific research agency.