WHAT IS IT about trans fat that makes me want to spend all night on Craigslist.org's rants and raves board? As of Jan. 1, 2006, we consumers will see yet another line item on nutrition labels: trans-fat content. According to a recent article in the Chicago Tribune, "The Food and Drug Administration estimates that within three years after trans fat food labeling is available, Americans will change their eating behavior, which will prevent 600 to 1,200 cases of coronary heart disease and 250 to 500 deaths per year." How realistic are these statistical projections, considering the negligible effect that nutritional labeling has had on health to date? Nutrition labeling on packaged foods has been mandatory in the United States for the past 13 years, but this has not made Americans healthier; quite the contrary.

Nutrition, according to a U.S. Department of Agriculture article ("What People Know and Do Not Know about Nutrition"), ranks second after taste in determining what foods people choose to buy. But this ranking doesn't reveal how much more influential taste is than nutrition as a deciding factor. Because trans fat improves taste, "mouth-feel" (industry-speak for texture), and shelf life, it lurks in most any snack food you might be tempted to grab – crackers, chips, cookies, even many supposedly healthy cereals. A form of fat created by adding hydrogen atoms to unsaturated fatty acids, trans fat (a.k.a. hydrogenated or partially hydrogenated oil) increases the risk of heart disease and raises LDL (bad cholesterol) levels. The double whammy: trans fat also lowers your HDL (good cholesterol). The chemistry of fats is fascinating stuff. For a simple explanation – with pictures! – check out "Questions and Answers on Trans Fat Proposed Rule" on the FDA Web site (www.cfsan.fda.gov/~dms/qatrans.html).

Americans aren't going to change their eating habits because of trans-fat labeling. There were plenty of reasons to drop the bag of Doritos even before trans fat reared its hydrogenated head on the nutrition roster. If, as the FDA anticipates, positive results from trans-fat labeling do come to pass, it will be because manufacturers are rushing to find substitutes for the trans fats in their products so they won't be vilified by the media and watchdog groups. Whole Foods is actually banning products with trans fat from its stores. Good-bye, Tofutti Cuties; au revoir, Mueslix.

Remember the years when butter was in the doghouse and margarine was the way to go if you were worried about your cholesterol? Well, now it turns out margarine is loaded with trans fat, a substance that currently enjoys roughly the same reputation as snake venom. Not to say that butter is back in favor; instead, margarine too has fallen from grace. It's no wonder that "many people find it difficult to put nutrition advice into practice, not least because they view the advice as ephemeral," as Marion Nestle writes in Food Politics. However, as Nestle points out in her enthralling study of the Byzantine chess games between federal regulatory bodies and the food industry, advice on healthy eating hasn't actually changed much in a long time: eat lots of plant matter (veggies and fruits) and stay in shape.

It can be easy to lose sight of this basic tenet in a thick smoke screen of information, hype, and advertising. My Yahoo! e-mail account runs nonstop banner ads for diets – Atkins, e-diets, the Zone – each contradicting the other on what foods to eat or not eat to achieve that model body. Down the street a billboard for Wheat Thins (major trans-fat offender) urges me to "Get Carried Away" with a cartoon of a tiny woman with a giant head getting lifted off the ground by a kite. A bag of chips or a cooking spray claims to be "fat free" by making the serving size absurdly small.

Speaking of fat and mixed messages, my favorite recent read is Jeffrey Steingarten's dogged collection of essays The Man Who Ate Everything, especially the piece, "Why Aren't the French Dropping like Flies?" The French, who eat "four times as much butter as we and more than twice as much cheese and lard" – foods high in saturated fat and containing trans fat – have the second-lowest rate of heart disease on earth. If your reaction to this news is anything like mine, a wide grin is slowly spreading across your face, and the strains of "Enjoy yourself, enjoy yourself, it's later than you think" have started warbling in your head. Presently, you will skip out of the house to twirl around a lamppost. I was lucky enough to have my skipping lead me to a sidewalk sale of cookbooks, where I picked up a long-coveted copy of The Cooking of Provincial France. Hello, butter, my old friend.