CDC: There's more trans fat lurking in U.S. foods than you think

Nearly 1 in 10 processed food products sold in the United States has trans fat in it - but you'd never know it by glancing at the nutritional label on the back of the package, according to a study released Thursday by the Centers for Disease Control and Prevention.

The report underscores the need to ban synthetically produced trans fat from all food products, public health experts said.

"The sense is that trans fat is mostly gone from foods, and what we see is there's still a lot being used in packaged foods," said Christine Curtis, assistant commissioner in the New York City health department and an author of the study. "We think consumers are unknowingly consuming artificial trans fat and the recommendation is to consume as little as possible."

Trans fat, which is made from a manufacturing process in which hydrogen is added to oil to make it solid, has been linked to a variety of health problems, but most directly to worsening cholesterol levels. Even relatively small doses of just a couple of grams a day can increase so-called bad cholesterols and reduce good cholesterols, studies have shown.

Consumption of trans fat has fallen in the United States since the first major warnings emerged from doctors and public health authorities a decade ago. Several state and regional bans - including one in California - have removed trans fat from foods sold in restaurants and bakeries.

But trans fat is still remarkably pervasive in the U.S. food supply, according to the new study, which was done by the New York City Department of Health and Mental Hygiene.

The study analyzed nutritional data for 4,340 products. Researchers found that 391 of those products, or about 9 percent, listed partially hydrogenated oils - the main source of manufactured trans fat - in their ingredient information. But 330 of those products claimed to have zero grams of trans fat per serving on their nutritional label.

The labeling may seem misleading, but it's allowed under a federal loophole that states products with less than 0.6 of a gram per serving can claim to have zero trans fat. And that could be dangerous for unaware consumers, doctors say. A fairly small bag of potato chips, for example, could have up to 0.5 of a gram of trans fat per serving, and if that bag contains three servings, a consumer could easily eat 1.5 grams of trans fat and not even know it.

"That's the biggest danger: You're going to think you're not getting any trans fat," said Dr. Junaid Khan, a cardiothoracic surgeon at Alta Bates Summit Medical Center. "The takeaway form this is not only do you have to read the label, but you have to understand serving size, and you have to know that even if it says zero trans fat it may still have trans fat."

The U.S. Food and Drug Administration is considering a policy that would officially deem partially hydrogenated oils unsafe. If the trans fats are found to be unsafe, food manufacturers would be required to remove them from all products.

In the meantime, public health and nutrition experts say, consumers should be wary of any processed foods - and read labels carefully. If a product claims to have zero trans fat, it's time to read the ingredient list and look for the words "partially hydrogenated" or the letters "PHO," which stands for partially hydrogenated oils.

Erin Allday is a San Francisco Chronicle staff writer. E-mail: eallday@sfchronicle.com Twitter: @erinallday