Trans fats have a well-earned bad reputation. For years, health officials have warned people to avoid industrial trans fats, the kind once widely found in partially hydrogenated oils used in some processed and fried foods.
But not all trans fats come from the same place. Small amounts also occur naturally in dairy foods such as milk, yogurt, butter and cheese. A new review suggests those naturally occurring dairy trans fats may not carry the same heart health risks as industrial trans fats.
The review, published in Nutrition Research, was funded by the National Dairy Council in the U.S. and the Centre National Interprofessionnel de l’Economie Laitière, a French dairy interbranch organization. Several authors also work for or receive funding from dairy industry or interbranch organizations, according to the University of Reading. That funding does not automatically discount the findings, but it is important context for a study focused on dairy foods.
Researchers analyzed evidence from 22 studies involving people in Europe, Canada and the United States. The review looked at two types of research: 10 controlled dietary trials that measured blood lipid biomarkers after people consumed dairy foods with naturally enhanced trans fats, and 12 long-term cohort studies that tracked blood levels of dairy trans fats and later cardiometabolic outcomes.
Professor Ian Givens, one of the study’s lead authors and a researcher at the University of Reading, said the findings may help clear up confusion over the word “trans fat.”
“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,” Givens said. “This research should give people reassurance that dairy, eaten as part of a balanced diet, is not something to worry about for your heart.”
Industrial trans fats are strongly linked to heart disease. They are created when liquid oils are partially hydrogenated, a process that makes fats more solid and shelf-stable. Because of those risks, partially hydrogenated oils have been removed or restricted in many food supplies.
Naturally occurring trans fats are different. They are produced in the digestive systems of ruminant animals such as cows, sheep and goats, which means small amounts can be found in dairy foods and some meats.
In the controlled trials included in the review, people consumed dairy foods with naturally enhanced trans fat levels and were compared with people consuming regular dairy foods. Across those trials, which involved trans fat intakes ranging from 1.3 to 13.2 grams per day, researchers reported no meaningful differences in blood lipid levels between the groups.
The long-term studies told a similar story. Those studies followed people for years, in some cases for more than two decades, and measured dairy trans fat levels in the blood. Higher levels were not linked with a greater risk of heart disease, stroke, cardiovascular death or type 2 diabetes.
That does not mean butter, cheese or whole milk should be treated as unlimited heart-health foods. The review focused on dairy trans fatty acids, not every nutrition question related to dairy fat. Dairy foods can vary widely in saturated fat, sodium, added sugar, calories, fermentation and overall nutrient profile. A sweetened yogurt, a piece of cheese and a glass of milk are not identical foods simply because they all contain dairy.
A trans fat listed on a food label may not tell the whole story about where that fat came from or how it behaves in the body.
That distinction can be confusing for consumers. For years, “trans fat” has been treated as a single category to avoid. Public health warnings have largely focused on industrial trans fats, which have clear evidence of harm. But dairy trans fats occur naturally in small amounts and include different fatty acids than those produced through partial hydrogenation.
The review adds to evidence suggesting naturally occurring dairy trans fats do not appear to raise cardiometabolic risk in the same way industrial trans fats do. Still, because the research was funded by dairy organizations, and because reviews depend on the quality and design of the studies they include, the findings should be interpreted with transparency and caution.
The bottom line is not that “trans fats are fine.” Industrial trans fats remain a concern and are best avoided. The more accurate message is that dairy trans fats appear to be a different story, and food labels do not always capture that nuance.