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Food fat lingers in older folks' blood.

Food Fat Lingers in Older Folks' Blood

It seems that everything slows down as we get older, and new findings on how we handle dietary fat bear this out.

Three years ago, a study at ARS' Human Nutrition Research Center on Aging at Tufts showed that older people have significantly more fat circulating in their blood after a fat-rich meal than younger people do. Since elevated triglycerides - as fats are called - contribute to the risk of heart disease, the finding has important implications.

While it could mean that older people absorb more fat than younger people, Ernst J. Schaefer and Jeffrey S. Cohn, who are with the center's Lipid Metabolism Laboratory, think it more likely that older people are simply slower at moving fat out of circulation.

To find out, they joined with Stephen A. Krasinski and Robert M. Russell, also at the center, who had found that older people also have higher blood levels of vitamin A than their younger counterparts. Since the vitamin is fat-soluble, it gets packaged together with triglycerides in intestinal cells before entering the blood and stays with the fat-rich particles in circulation. So they reasoned they could use vitamin A as a marker to gauge how fast the body cleared dietary fats from the blood by measuring the vitamin's clearance rate.

Eighteen men and women - half of them under 30 years old and the other half over 60 - participated in this study. After an overnight fast, they ate a meal of soybean oil containing a large dose of retinyl ester - a form of vitamin A - as the marker. Then each donated about a pint of plasma, which was reinjected 2 days later after another overnight fast. By withdrawing blood samples before and at regular intervals after the plasma infusion, the researchers tracked the disappearance of infused vitamin A and related that to triglyceride levels throughout the same period.

"Vitamin A remained in the blood of the over-60 group almost twice as long as it did in that of the under-30 group," says Schaefer, a medical doctor who oversees lipid metabolism research at the center. "Mean residence time of the vitamin was 57 minutes in the older group and 31 minutes in the younger. We think the difference is due to less active liver receptors," he says, referring to the proteins on the surface of liver cells that usher these fat-rich particles inside.

Schaefer says, "This is another good reason for older people to restrict their fat intake to some extent - these particles potentially lead to plaque buildup." - By Judy McBride, ARS.
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Title Annotation:triglycerides purge faster from the blood streams of the young than the old
Author:McBride, Judy
Publication:Agricultural Research
Date:Jan 1, 1991
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