If you keep milk, butter, yogurt and cheese in your fridge, a review of 22 studies gives you clearer footing for that choice: the trans fats these dairy foods naturally contain were not linked to a higher risk of heart disease, stroke, cardiovascular death or type 2 diabetes. The research was published in the journal Nutrition Research, with lead authors from the University of Reading. It separates the natural trans fats in dairy from the industrial trans fats made from partially hydrogenated oils that have long been tied to cardiovascular harm.
The review pooled two kinds of evidence from thousands of participants in Europe, Canada and the United States. One set measured blood fats in controlled feeding trials. The other tracked health outcomes over many years in long-term cohort studies. Across both, the controlled trials showed no significant differences in blood lipid biomarkers apart from a slight decrease in HDL-C, and in the long-term studies higher blood levels of dairy trans fats were not associated with an increased risk of heart disease, stroke, cardiovascular death or type 2 diabetes.
What did the controlled trials measure?
The first set of evidence came from ten controlled dietary trials. In each, participants ate dairy foods with naturally enhanced levels of trans fats, produced by altering the cow’s diet, and were compared with people eating regular dairy. Scientists then measured blood lipid biomarkers commonly used to assess heart disease risk. Daily trans fat intake across the trials ranged from 1.3 to 13.2 grams.
Across the ten trials there were no significant differences in blood lipid biomarkers between the two groups, apart from a slight decrease in HDL-C. The paper, published in Nutrition Research (Elsevier), reports that among the ten trials “there were no significant differences in mean difference for any lipid biomarkers except for a slight decrease in HDL-C (mean difference: -0.05 mmol/L; confidence interval: -0.10 to -0.00) for TFA-enriched vs. regular dairy foods.” HDL-C is high-density lipoprotein cholesterol.
What did the long-term studies show?
The second set came from twelve long-term cohort studies that followed thousands of people over many years, with some running more than two decades. Researchers measured concentrations of dairy trans fats in participants’ blood, specifically trans vaccenic acid and trans palmitoleic acid, and compared them with later health outcomes.
Higher blood levels of these dairy trans fats were not associated with a higher risk of heart disease, stroke or cardiovascular death. They were also not associated with a greater risk of developing type 2 diabetes. The research is described as first-of-its-kind and could help consumers better understand the distinction between different types of trans fats.
Why natural and industrial trans fats differ
Trans fats are a type of unsaturated fat. They occur naturally in the milk of cows, sheep and goats, and they can also be produced artificially during the manufacture of partially hydrogenated fats. Industrial trans fats, found in some processed and fried foods, have been strongly linked to an increased risk of heart disease. The review found that naturally occurring dairy trans fats act differently in the body from industrial trans fats.
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.”
The research could provide greater clarity around labeling policies that may contribute to confusion. Industrial trans fats, which can be present in some processed and fried foods, have been strongly linked to an increased risk of heart disease.
What to do now
- Read ingredient lists for “partially hydrogenated” oils.
- If you track your cholesterol, note that the trials found no meaningful change in blood lipids from higher-trans-fat dairy, aside from a slight HDL-C decrease whose confidence interval reached zero.
FAQ
Are the trans fats in dairy harmful?
According to a review of 22 studies published in Nutrition Research and led by researchers at the University of Reading, the trans fats naturally present in milk, butter, yogurt and cheese were not linked to a higher risk of heart disease, stroke, cardiovascular death or type 2 diabetes.
How many studies did the review include?
The review drew on ten controlled dietary trials and twelve long-term cohort studies, covering thousands of participants in Europe, Canada and the United States. Some of the cohort studies followed participants for more than two decades.
Are dairy trans fats the same as industrial trans fats?
No. Industrial trans fats come from partially hydrogenated oils used in some processed and fried foods and have been strongly linked to heart disease. Natural dairy trans fats come from the milk of cows, sheep and goats and, based on the evidence in this review, did not show the same risk.
