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A new study out of McMaster University says trans fats are linked to a greater risk of heart disease and death, but saturated fats are not.

The paper published today by the British Medical Journal with dietitian Russell deSouza as the lead author, analyzed data from over 70 studies on the long term effects of trans fats and saturated fats. They found that people who ate trans fats were, on average, 34% more likely to die and 28% more likely to have heart disease. Even people who ate refined sugar in place of trans fats had a lower risk of death.

But they didn’t find the same clear associations for saturated fats. People who ate saturated fats were no more likely to have heart disease or die than people who didn’t.

Trans fats were originally created in the early 1900s as a cheap, shelf stable alternative to products like butter. They start as healthier oils, like canola, that are liquid at room temperature then they’re injected with hydrogen and become more solid, like shortening. Their structure isn’t all that different than saturated fats but something about them makes them much more dangerous.

Trans fats are found in processed foods, including canned frosting, store bought baked goods, some microwave popcorns, coffee whiteners and sometimes shortening. The words ‘partially hydrogenated vegetable oil’ in an ingredient label indicates trans fats. They will also be listed in nutritional information. If they account for more than 5% of a product’s fat content, it’s considered to have a significant level of trans fat, but deSouza recommends avoiding them all together.

And while researchers didn’t find a clear case against saturated fats, they still suggest consuming less of them and opting for unsaturated fat sources instead, like vegetable oils, olive oil and nuts.