Trans in trouble.
August 1990: Millions swear they'll never again believe another word of nutrition advice.
Why? A new study says that trans fatty acids are bad for your heart. Suddenly, folks are (mistakenly) saying that butter is better than margarine.
It's not just margarine that's at stake. Trans fatty acids are found in shortening and hundreds of cakes, cookies, chips, and fried foods that are made with "partially hydrogenated" oils.
Earlier charges that trans fatty acids cause heart disease or cancer have never held up (see NAH, March 1988). But a new study, by Ronald Mensink and Martijn Katan, of the Agricultural University in the Netherlands, raises important questions.
That's not to say trans fatty acids are artery-cloggers. A broad study with such implications must be confirmed. And the fats in our foods may effect cholesterol differently than those used in the Dutch experiment.
Until the early 1990s, if you wanted a solid fat for your pie crust, you had to choose between lard, butter, or beef tallow. In 1911, Procter and Gamble changed all that when it introduced Crisco, a shortening made by hydrogenating a liquid oil (cottonseed).
Hydrogenating--or adding hydrogen--makes oils more solid, in part because they end up somewhat more saturated. And saturated fats stay solid at room temperature.
Hydrogeneration also converts some of the oil's monounsaturated (and a few of its polyunsaturated) fats from the naturally occurring cis structure to a trans structure.
Trans fats are "stiffer," which helps keep the oil from oozing out of your brownies or potato chips. And, trans fats are listed as unsaturated fats on product labels--a plus for companies tyring to woo consumers.
The question is, do trans fats raise or lower your blood cholesterol? That's what Mensink and Katan tried to find out.
The Dutch researchers fed 59 young men and women three almost identical diets for three weeks each. (1) The only difference was that ten percent of the calories came from one of three fats:
* oleic acid, the monounsaturated cis fatty acid normally found in olive oil,
* the trans version of oleic acid, or
* a saturated fat.
The people eating the trans fats ended up with higher total and LDL ("bad") cholesterol than those eating the cis fats, though not as high as those eating the saturated fats. Worse yet HDL ("good") cholesterol levels were lowest on the trans-fat diet.
The drop in HDL, combined with the rise in LDL, made the trans fats "at least as unfavorable as...the cholesterol-raising saturated fatty acids," concluded Mensink and Katan.
Because the Dutch team set out to compare monounsaturated trans fats to their cis cousins, they used "margarines" that were formulated to contain high levels of those fatty acids. That raises several questions:
* Would the polyunsaturated fats in ordinary margarine counteract the damage done by the trans fats? Since polys lower cholesterol levels, margarine's impact may not be so bad. On the other hand, "Mensink's and Katan's trans diet might be closer to the composition of vegetable-oil shortenings, which tend to be lower in polyunsaturated fats thn margarines," says Edward Emken, of the U.S. Agricultural Research Service in Peoria.
* Would a smaller amount of trans have a negligible effect? Most Americans eat about four to seven grams of trans fatty acids per day, says Emken. The Dutch-study participants ate 33 grams.
* Would trans fats produced by hydrogenation have the same effect? Rather than hydrogenate their oils, the Dutch researchers converted cis fats directly to trans by a process called isomeration.
"With isomerization, you get a lot of other fatty acids that aren't in our shortenings and margarines," says Fred Mattson, a hydrogenation expert formerly with Procter and Gamble and the University of California School of Medicine in San Diego.
* Would a longer study on different people yield different results? "I'd like to see a five to six week study, because it takes a little longer than three weeks for cholesterol levels to stabilizeM," says Emken.
What's more, the young adults in the Dutch study had low cholesterols. "Work needs to be done with a middle-aged population with cholesterols in the 220 to 280 range," says Emken. "If trans fatty acids lower their DHL, there's more reason to be concerned."
THE BOTTOM LINE
Trans, shmans. You should eat less fat to avoid cancer and obesity, not just heart disease. That includes fatty fried or baked goods made with partially hydrogenated oils.
But don't switch back to butter--it's saturated fat and cholesterol are known arterycloggers. Instead, use a teaspoon or two of olive oil for cooking. And if you can't dab oil on your bread (as they do in the Mediterranean), use a soft tub diet margarine, not a stick.
(1) N. Eng. J. Med. 323:439, 1990.