Chocolate: heart-ier than you thought.

Although a saturated fat, stearic acid is unusual in that consumption of it does not raise concentrations of cholesterol in the blood. Why remains a mystery, though not for lack of investigation, notes Edward A. Emken of the Agricultural Research Service (ARS) in Peoria, Ill. He fed a deuteriumtagged quantity of five different fats -- including the saturated stearic and palmitic fatty acids -- to seven men.

Over the next 2 days, he monitored how their bodies converted and incorporated those fats. Animal data, he notes, had suggested that the body might not absorb stearic acid well, or preferentially converts most of it to a monounsaturated fat that would therefore have no effect on cholesterol.

But in a December supplement to the AMERICAN JOURNAL OF CLINICAL NUTRITION (AJCN), which focuses on stearic acid's effects, Emken reports finding that "no single metabolic difference between the [two saturated fats] is sufficiently large enough to fully explain the lower cholesterolemic effect of stearic acid."

He did detect small differnces in the fats' absorption, in their rates of desaturation (loss of hydrogen from the fats' chainlike backbone of linked carbon atoms), and in their incorporation by tissues. But at best, he says, these offer only a partial explanation of stearic acid's unusual cholesterol effect.

Emken's colleagues at ARS labs in Beltsville, Md., and San Francisco identified other differences in the way the body handles the two fats. Ten men who switched from a diet high in palmitic acid to a diet high in stearic acid formed smaller and apparently less activated blood platelets -- clot-forming elements in the blood. Moreover, their blood clotted more slowly during the stearic-rich portion of the 11-week study, Norberta W. Schoene and her coworkers report in the AJCN supplement. As a result, they conclude, these fats should not be seen as comparable risks for clot-based strokes.

Cholesterol watchers with a "fat tooth" can find stearic acid among the mix of fats in lean beef and other meats. But cocoa butter represents a concentrated source. In fact, a relatively fatty milk chocolate bar can be swapped for a low-fat daily snack possessing the same calories without raising low-density lipoproteins in the blood-- a major risk factor in heart disease. At least that's what Penny M. Kris-Etherton of Pennsylvania State University in University Park and her coworkers observed in their 14-week study involving 42 young men. It is also described in the December AJCN supplement.