Fatty complexities.

Fatty Complexities

George Kamilar thought he had finally figured it out. For people with high cholesterol, chicken and fish were safe, meat was not. But then he heard about a study saying beef and chocolate do not raise cholesterol. "It's very confusing," says Kamilar. "There's so much information bombarding you, you don't know what to believe."

George Kamilar isn't the only person feeling confused these days. A recent study from the University of Texas sent shock waves through the medical community. It confirmed what researchers have suspected for years: All saturated fats are not created equal.

But the new study isn't as promising as chocaholics and the meat industry would have us believe. In short, beef and chocolate are not yet off the hook.

You might say Scott Grundy has done it again. Two years ago, the researcher at the University of Texas reminded the nutrition world that monounsaturated fats like olive oil have a place in a diet designed to lower blood cholesterol. Previously, experts had overlooked monos, encouraging people to eat more polyunsaturated fats only. But compared to highly saturated fats, both monos and polys lower cholesterol.

In 1988, Grundy made headlines once again. This time, he tackled stearic acid, a saturated fat found in beef, chocolate, and many other foods. To understand his findings, you have to first know what fats are made of.

FAT FUNDAMENTALS

The backbone of every fat molecule is glycerol, a slippery liquid used to make soaps and skin lotions. Attached to this backbone are two or three branches. These are the fatty acids that make such a difference in a fat's impact on health.

Some fatty acids are saturated with hydrogen atoms. Others are mono-unsaturated--that is, there's room for more hydrogens at one location on the branch. Still others are poly-unsaturated. They have room for more hydrogens at several locations.

You may wonder what hydrogen atoms have to do with blood cholesterol. So do researchers. So far, they don't know exactly why unsaturated fatty acids tend to lower blood cholesterol levels. Nor do they understand why saturated fatty acids raise cholesterol. They only know it happens.

Or at least, it usually happens. Grundy and co-worker Andrea Bonanome showed that stearic acid is one of the few saturated fatty acids that does not raise cholesterol. [1] They weren't the first to notice stearic acid's unexpected behavior. Ancel Keys, then with the University of Minnesota, and Mark Hegsted, now with Harvard's New England Primate Research Center in Massachusetts, independently published similar findings more than 20 years ago.

"In the early sixties, we found that cocoa butter raises cholesterol less than it ought to based on its saturated fat content," says Hegsted. "That led us to look at stearic acid."

In fact, stearic acid isn't the only saturated fatty acid that fails to raise blood cholesterol. Butyric, caproic, caprylic, and capric acid don't either.

Researchers don't know what makes stearic acid unusual, but do have a clue that might explain why these four saturated fatty acids appear to be safer than others. Their shorter size seems to be responsible. Longer fatty acids pass from the intestines into lymph ducts, which dump them into the general bloodstream where they can clog blood vessels.

In contrast, short- and medium-chain fatty acids bypass the lymphatic system. They are absorbed into a vein that goes directly to the liver, where they are likely to be "burned" for energy.

FROM FATTY ACIDS TO FOODS

What Grundy and Bonanome fed the volunteers in their study, you wouldn't serve to guests. It was a liquid formula consisting of 40 percent sugar, 20 percent casein (a milk protein), and 40 percent fat. The fat was soybean oil, heavily hydrogenated and processed so that half of it was stearic acid, and roughly half was monounsaturated.

All that processing was necessary because nature doesn't make fats that contain only one saturated fatty acid. And that's precisely why Grundy's study--for all its elegance as a scientific experiment--won't lead to major changes in what George Kamilar eats.

Take beef, for example. Roughly half of its saturated fat is stearic acid, but the other half is largely palmitic acid, which does hike blood cholesterol levels. The same holds true for chocolate.

What's more, beef is so fat-laden that even without stearic acid, it still adds a bellyful of saturated fat to the average person's diet. Red meat (beef and pork) is the largest source of cholesterol-raising fat in the average American's diet. [2] Plus, beef contains an additional slug of cholesterol, which has its own power to raise blood cholesterol.

And even if all the fat in beef or chocolate were heart-healthy, we would still need to watch our intake, because fat of any kind is loaded with calories and also appears to boost the risk of breast and colon cancer.

In an editorial accompanying the study in The New England Journal of Medicine, Irwin Rosenberg and Ernst Schaefer of Tufts University said as much. [1] "This study should not change our chief dietary message to the American public," they concluded.

Even Grundy's staff changed its tune after the original press releases went out. "When the study was released, we saw a lot of dumb headlines saying you can eat beef and lower your cholesterol," says Tommy Bosler, spokesperson for the University of Texas. "But our study was done with pure stearic acid, and people eat food."

That wasn't the only point of confusion. "Stearic acid only lowers cholesterol when it's replacing cholesterol-raising saturated fats in the diet," explained Bosler. "It's misleading to call stearic a cholesterol-lowering fat."

The study does have other implications. Corporate research offices are probably already buzzing with plans to create Crisco-like shortenings made almost exclusively of stearic acid. Such a fat would presumably make a flaky pie crust without leaving a crust on your arteries.

Finally, the new research will almost certainly spawn fresh claims of innocence by the meat and chocolate industries (see box). These claims--which could even appear in advertising--will probably throw consumers like George Kamilar into a cloud of confusion.

"After a while, you begin to wonder who's right," says Kamilar. "And when it comes to food, doctors are no help at all."

[1] N. Eng. J. Med. 318: 1244, 1270, 1988.

[2] Am. J. Epidem. 122: 27, 1985.

[3] Nutr. Res. 8: 287, 1988.

[4] J. Nutr. 85: 67, 1965.

[5] Lancet 1: 1105, 1960.

[6] J. Nutr. 76: 255, 1962.

[7] J. Amer. Oil Chem. Soc. 35: 10, 1958.

[8] Can. J. Biochem. Physiol. 37: 575, 1959.

[9] Nutr. Rev. 45: 205, 1987.

[10] Nutr. Rev. 46: 173, 1988.