USDA-ARS Investigates Why Whole Grains Aid Heart Health

A new study by USDA's Agricultural Research Service (USDA-ARS) aims to demonstrate why a diet rich in whole-grain foods has the ability to help keep triglyceride levels down when compared to a diet heavily--or completely--based on refined grains. According to a recent USDA-ARS report written by Marcia Wood, public affairs specialist, ARS, and published in Agricultural Research (2006; 54, 3:20-21), components in whole grains have the ability to block two very low-density lipoproteins (VLDLs), triglyceride and apolipoprotein CIII (apoCIII), both of which have been shown to increase the risk of heart disease.

Generally, high-density lipoproteins (HDLs) are considered "good" cholesterol, while health professionals have tagged LDL cholesterol with the "bad" moniker. VLDLs are the precursor to LDLs: VLDLs circulate through the blood, releasing triglycerides to fat and muscle tissue, until any remaining VLDLs are modified and converted into LDLs.

"In medical studies, apoCIII has been associated with high levels of triglycerides and increased risk of heart disease," notes Nancy L. Keim, the ARS research chemist who designed and led the whole-grain investigation at the Western Human Nutrition Research Center, Davis, CA. Studies have also shown that apoCIII interferes with lipoprotein lipase's ability to remove triglycerides from LDLs so that the triglycerides can be used or stored.

"VLDLs are naturally rich in triglycerides, so you want the lipoprotein lipase--your triglyceride-removing mechanism--to be very efficient," says Keim. "If the apoCIII protein on your VLDLs slows down the lipoprotein lipase, triglycerides may spend more time in your VLDLs instead of where they belong--in your muscles or fat tissue. The longer the triglycerides remain in your VLDLs, the more likely they are to be oxidized or to infiltrate your arteries. Neither outcome is good."

The study involved 10 women, age 20 to 45, who followed alternating whole-grain and refined-grain diets. According to the ARS report, during the first three days of the whole-grain phase, the subjects ate an average of six to eight servings of whole-grain foods, such as whole-grain breakfast cereal, pearled barley and rye crackers, every day. When on the refined-grains diet, the women ate such foods as refined-grain breakfast cereal, white rice and graham crackers. On the fourth day of each portion, the women ate breakfast at the Nutrition Research Center and provided blood samples for analysis. A follow-up study that will last for a longer duration and will include more subjects--including a mix of both men and women--is scheduled to begin later this year.

The 2005 Dietary Guidelines for Americans recommends that we eat three or more ounce-equivalent servings of whole-grain foods every day; an "ounce-equivalent" can include one slice of whole-grain bread, a cup of dry whole-grain cereal or one-half cup cooked whole-grain rice or cereal. However, the ARS report notes that current estimates have determined that 95% of Americans eat less than one serving per day. According to the Whole Grains Council, Boston, nearly half of all Americans do not eat any whole grains on a daily basis.

As Wood notes in her report, "Maybe results of Keim's investigations will be just the nudge we need to ensure that we get our daily measure of these nourishing grains."