Researchers reviewed evidence from 22 studies involving thousands of participants in Europe, Canada and the United States. Their findings indicate that naturally occurring dairy trans fats act differently in the body from industrial trans fats. While industrial trans fats are strongly associated with heart disease, the naturally occurring forms found in dairy did not appear to carry the same risk.

The first-of-its-kind research, published in the journal Nutrition Research, could also help consumers better understand the distinction between different types of trans fats and provide greater clarity around labeling policies that may contribute to confusion.

Professor Ian Givens, one of the lead authors from the University of Reading, said: "People hear the words 'trans fats' and assume the worst, but the trans fats in your morning milk, yogurt, butter or cheese are not the same as the ones from industrial partially hydrogenated fats. This research should give people reassurance that dairy, eaten as part of a balanced diet, is not something to worry about for your heart."

Natural and Industrial Trans Fats Have Different Effects

Trans fats are a type of unsaturated fat. They occur naturally in the milk of animals such as cows, sheep, and goats, but they can also be produced artificially during the manufacture of partially hydrogenated fats.

Industrial trans fats, which can be present in some processed and fried foods, have been strongly linked to an increased risk of heart disease. The researchers wanted to determine whether the trans fats naturally found in dairy foods should be viewed in the same way.

Controlled Trials Find No Meaningful Change in Blood Lipids

The researchers examined two main types of evidence. The first came from ten controlled dietary trials in which participants consumed dairy foods containing naturally enhanced levels of trans fats and were compared with people consuming regular dairy products.

Scientists then measured blood lipid biomarkers that are commonly used to assess heart disease risk. Across all ten trials, participants consumed between 1.3 and 13.2 grams of trans fat per day.

The results showed no meaningful differences in blood lipid levels between those consuming dairy foods with higher levels of natural trans fats and those consuming regular dairy products.

Long-Term Studies Show No Higher Heart or Diabetes Risk

The second group of evidence came from twelve long-term cohort studies that followed thousands of people over many years, with some studies lasting more than two decades.

Researchers measured levels of dairy trans fats in participants' blood and compared them with later health outcomes. Across these studies, higher levels of dairy trans fats were not associated with an increased risk of heart disease, stroke or cardiovascular death.

Higher blood levels of dairy trans fats were also not associated with a greater risk of developing type 2 diabetes.