Consumers who see 0 g trans fat on the Nutrition Facts label are probably unaware that they are consuming trans fats, U.S. researchers say. (Damian Dovarganes/Associated Press)

Nearly 10 per cent of top-selling packaged foods in the U.S. contain trans fats — and many of them are labelled as having zero grams per serving, says a new study published Thursday.

The study, published in the Centers for Disease Control and Prevention (CDC) journal Preventing Chronic Disease, looked at 4,340 packaged foods and found that nine per cent of those products contained partially hydrogenated oils.

"These findings, which are consistent with FDA research findings, provide evidence of the prevalence of industrial trans fat and show that most products that contain partially hydrogenated oils are labelled as containing zero grams of trans fat (84 per cent)," Jennifer Clapp, acting director of healthy eating and active living at New York City's health department and her co-authors concluded.

Food manufacturers use trans fats to extend shelf life. Consuming trans fat raises low-density lipoprotein (LDL), or "bad" cholesterol and increases the risk of heart disease, experts say.

The U.S. Food and Drug Administration has tentatively determined that partially hydrogenated oils, the main dietary source of industrial trans fat, are not "generally recognized as safe" for consumption.

"This labelling is cause for concern because consumers, seeing the 0 g trans fat on the Nutrition Facts label, are probably unaware that they are consuming trans fats," said Clapp.

Companies are allowed to label products as having zero trans fat as long as the amount is limited to 0-0.5 grams of trans fat per serving.

In the study, over half of food categories had at least one product with partially hydrogenated oils, including baked goods and snack foods such as cookies, crackers and frozen entrees.

The study was funded by philanthropists and donors including the WK Kellogg Foundation and the U.S. Department of Health and Human Services.