Eating trans fat can take years off of your life. And you may be eating it in chips, crackers, and baked goods and not even know it.

Trans fat is created when vegetable or other oils are pumped with hydrogen at high temperatures. This process creates partially hydrogenated oil, an ingredient that lends manufactured foods like cookies and crackers a crispness and prolonged shelf life. Food product manufacturers have used partially hydrogenated oil in packaged food extensively since the 1920s, but scientists have increasingly recommended since the 90’s that consumers avoid it due to its harmful health effects.

In its 2002 report based on numerous studies linking trans fat to coronary heart disease, the National Academy of Sciences (NAS) concluded that “the only safe intake of trans fat is ‘zero.’” In 2006, a comprehensive review of studies of trans fat that was published in the New England Journal of Medicine concluded that, “On a per-calorie basis, trans fats appear to increase the risk of coronary heart disease more than any other macronutrient.” Other studies have suggested a link between trans fat consumption and increased risks for cancer, diabetes, Alzheimer’s disease, liver dysfunction, obesity, and infertility.

Since 2006, the Food and Drug Administration (FDA), motivated by the NAS report, has mandated that food product manufacturers list trans fat content on their products’ Nutritional Facts panels. Manufacturers responded by reducing the amount of trans fat in many of their products so they wouldn’t be viewed as unhealthy by consumers. This is where it gets tricky.

The FDA rules for the Nutritional Facts panels that appear on all retail food products allow for rounding; if there is less than half a gram of trans fat in one serving, then the trans fat amount in the panel is rounded down to “0 grams.” However, if you look at the ingredients list of many of these “zero trans fat” snack foods, “partially hydrogenated oil” is listed among the ingredients. If hydrogenated or partially hydrogenated oil appears in the ingredients list, and you’re eating what’s in the package, you’re consuming trans fat.

So if you want to live a long, healthy life, make sure you read the ingredients before you purchase or consume a food product to verify that partially hydrogenated oil is not on the list.