For years, medical experts and the Food and Drug Administration (FDA) have called trans fatty acids (TFAs), aka trans fat, the bane of the American diet. They say it can lead to memory loss, contribute to diabetes, and heighten risk of death. Trans fats are so bad that food manufacturers have hidden them in food, trying to trick consumers into eating what could potentially harm them. However, a new study published in the European Heart Journal has found that trans fats might not be as bad as people think.

Before you start gobbling down McDonald’s fries or an entire package of Oreos, let’s clear something up: Trans fats are still bad for you in large quantities, but low levels of them may not be as harmful, according to study researchers led by Dr. Marcus Kleber, a post-doctoral researcher at the Vth Department of Medicine at Heidelberg University in Germany. In fact, Kleber’s team found that low levels of artificially manufactured trans fats weren’t as harmful, while naturally occurring ones that appeared in foods, like dairy and meat products, could even be beneficial.

Artificial trans fats are produced when hydrogen is added to liquid oil to solidify it, a process called hydrogenation. Trans fats are used in everything from the aforementioned McDonald’s fries, to cakes, pies, biscuits, and basically any fried item. Consuming high levels of trans fats can lead to high blood pressure, heart problems, stroke, diabetes, and possibly even infertility, Alzheimer’s, and some forms of cancer.

For the study, Dr. Kleber and his team looked at data from the Ludwigshafen Risk and Cardiovascular Health (LURIC) study, which took place between 1997 and 2000 and involved 3,316 people who had signed up after undergoing coronary angiographies to determine cardiovascular health. Kleber’s study involved 3,259 of these people, 30 percent of whom died over the course of the 12 years.

The researchers analyzed the red blood cell membranes of patients to find their total concentrations of trans fats, as well as to distinguish between concentrations of artificial and natural trans fats. Using the blood samples, they compared it to information on deaths, causes of death, medical histories (particularly diabetes and blood pressure), and other factors, such as whether a patient was taking cholesterol-lowering drugs, how much they exercised, and if they smoked.

“We found that higher concentrations of TFAs in the membranes of red blood cells were associated with higher LDL or 'bad' cholesterol, but also with lower body mass index, lower fats in the blood (triglycerides), and less insulin resistance and, therefore, a lower risk of diabetes,” Kleber said in a press release. “We were surprised to find that naturally occurring TFAs were associated with a lower rate of deaths from any cause, and this was driven mainly by a lower risk of sudden cardiac death.”

Kleber was surprised to find “that increases in the concentrations of industrially produced TFAs were not followed by increased mortality.” This differs from studies done in the U.S., and Kleber believes it was because the German participants showed lower levels of trans fats in their blood than what might be found in a typical American.

The patients with the highest concentrations of naturally occurring trans fats also had a 37 percent lower chance of sudden cardiac death when compared to those with lower levels. The associations between naturally occurring and industrially made trans fats and death were not statistically significant, the study found.

“Our results show that the low levels of industrially produced TFA we found in the LURIC study did not pose a health risk, and therefore could be regarded as safe,” Kleber said. “We also found that trans-palmitoleic acid (a naturally occurring TFA found in milk and meat from ruminant animals [like cows and sheep]) is associated with better blood glucose levels and fewer deaths from any cause, but especially a lower risk of sudden cardiac death.”

Source: Kleber, M, et al. Trans Fatty Acids and Mortality in Patients referred for Coronary Angiography - The Ludwigshafen Risk and Cardiovascular Health Study. European Heart Journal. 2015.