On Thursday the FDA made the surprise announcement that it would move to ban artificial trans fats, which are found in foods containing partially hydrogenated vegetable oils. The ban would not apply to naturally occurring trans fats, such as those found in meat and dairy products. Adoption of the proposal, which is open to public comment until Jan. 7, 2014, would mean that food producers who want to use partially hydrogenated oils would first have to prove to the FDA the safety of the ingredient.

Considering that the FDA's announcement this week declared preemptively "that there is no safe level of consumption of artificial trans fat," the burden of proof for future trans fat use would appear to be quite high.

What does trans fat research say?

Studies on artificial trans fats have found generally that they raise the amount of bad cholesterol (LDL) and lower the amount of good cholesterol (HDL) in the blood. (More here on HDL and LDL generally.)

But a recent meta analysis, Effect of Animal and Industrial Trans Fatty Acids on HDL and LDL Cholesterol Levels in Humans—A Quantitative Review, published in the open-access, peer-reviewed journal PLOS ONE in 2010, concludes that those negative effects may also be shared by natural trans fats. The study looked at the results from twenty-nine human studies in which subjects were fed artificial trans fats and six studies in which subjects were fed natural trans fats derived from milk fat. It found the impact of artificial and natural trans fats on HDL and LDL levels to be roughly equivalent.

Like the 2010 PLOS ONE study, a 2005 book by the Institute of Medicine that appears to form much of the basis for the FDA's action (the agency went so far as to link to it in yesterday's FDA press release) appears to make no distinction between artificial and natural trans fats.

What's more, the IOM appears torn over trans fats. On the one hand, it refers to them as "not essential" and says they "provide no known health benefit." The FDA cites these points, of course. But the IOM also concludes in the same paragraph "trans fatty acids are unavoidable in ordinary, nonvegan diets."

How much trans fats do we eat?

Thanks to the fact many food producers have responded to consumer demand and removed trans fats from their foods in recent years, the FDA's press release noted that "trans fat intake among American consumers has declined from 4.6 grams per day in 2003 to about 1 gram per day in 2012."

The American Heart Association, meanwhile, suggests Americans consume "less than 2 grams of trans fats a day." So if the FDA and AHA are correct, then current consumption levels—prior to and without any ban—are well within safe levels. Still, that didn't stop the AHA from endorsing the FDA's suggested ban.

And what about natural trans fats? According to the USDA, a pound of ground beef contains more than 8g of trans fat.

What is the FDA doing?

The FDA has required food labels to list trans fat content since 2006. As I've written before, though, where a warning will suffice, a ban is inappropriate. Here, it's also exceptional.

Attorney Mark Itzkoff told Politico that the FDA's move against trans fats was "virtually unprecedented."

Virtually, indeed.

Recall that the FDA forced Four Loko and other beers containing caffeine from the market in 2010, though the agency's procedural machinations were slightly different with Four Loko than they are with trans fats.

More recently, as I wrote about here, the FDA has been rattling its saber in the direction of caffeine, which could face a similar fate if the agency's move against trans fats is successful.

What would be the impact on food?

The proposed ban has already spurred its share of culinary requiems. Time has written obituaries for doughnuts, crackers, frozen pizza, coffee creamer, ready-made doughs, canned frosting, and some popcorn. Fox News, meanwhile, is mourning microwave popcorn, cookies, crackers, refrigerated dough, pie crust, margarine, and coffee creamer. Politico reported the ban could make foods taste worse and could also "could increase the saturated fat content of foods," since something will have to replace trans fats in the foods that presently contain them, and that something is simply different saturated fats.

Do trans fat bans work?

New York City banned trans fats in 2006. The ban was phased in gradually over two years. At least one study has shown what one might expect—that the city's trans fat ban caused New Yorkers to consume less trans fats. So trans fat bans work insofar as they ban some trans fats. But are New Yorkers healthier as a result? That's a more complicated question than it might first appear.

"Further reduction in the amount of trans fat in the American diet could prevent an additional 20,000 heart attacks and 7,000 deaths from heart disease each year," claimed the FDA as it announced its proposed ban.

Sure enough, according to my analysis of CDC data, New York City's rate of mortality from heart disease fell by 7.3% from 2006 to 2010.

Case closed? Not quite.

According to my analysis of CDC data, the national rate of mortality from heart disease fell by 9.3% during that same period. Obviously, the national decline—the rate of which was 21.5% higher nationwide than that found in New York City—can't be attributed to a national trans fat ban that has yet to take place.

What's more, consider that New York City also banned smoking in bars and restaurants in 2003. Smoking is a leading cause of heart disease and related death. New York City's overall smoking rate has fallen from 21.5% in 2002 to 14.8% percent in 2011 and to 14% today.

Though smoking rates have fallen nationally over the same period, from 20.9% in 2005 to 18.0% in 2012, according to CDC data, the smoking rate across the country is still higher than it is in New York City. And yet the national rate for deaths caused by heart disease fell by a greater percentage nationwide than it did in New York City from 2006-2010.

Do trans fat bans save lives? The burden of proof is on the FDA.

What's next?

The FDA will move to ban trans fats in a matter of months, after reviewing public comments on its proposal. It's clear that there are holes in the FDA's argument—many of which pertain to what appears to be the similar impact of artificial and naturally occurring trans fats. Perhaps opponents of meat consumption, including animal rights groups, might use this information to mount a legal challenge to prohibit the sale of beef and other foods that naturally contains trans fats. That idea may seem farfetched, but none too long ago so might have the FDA's Four Loko ban, its crackdown on caffeine, and the frontal assault it launched this week on artificial trans fats.