Natural trans fat in dairy did not raise heart disease risk in a new review

Trans fat has had one reputation for twenty years: the thing nutrition labels started listing because it was worse than saturated fat, and the thing the FDA spent most of a decade pushing out of the food supply. A review published this year complicates that reputation, for one specific category: the trans fat that occurs naturally in dairy.

The study

A systematic review and meta-analysis led by Constance Gayet-Boyer, with co-authors including D. Ian Givens at the University of Reading, pooled 22 studies: 10 randomized controlled trials and 12 prospective cohort studies, drawn from Europe, Canada and the United States. It was published in Nutrition Research (volume 150, pages 33 to 48), posted online in March 2026 and covered as news through October, after the University of Reading's press office promoted it.

The trials tested diets enriched with dairy trans fat against regular dairy, with intakes ranging from 1.3 to 13.2 grams a day, and measured standard cholesterol and lipid markers. Across all 10 trials, the only statistically significant difference was a small decrease in HDL cholesterol (mean difference −0.05 mmol/L) in the higher-trans-fat group, not an increase in anything considered harmful. The 12 cohort studies, which measured circulating levels of the dairy trans fats vaccenic acid and trans palmitoleic acid in people's blood and followed them over time, found no association between higher levels of either compound and cardiovascular disease, cardiovascular death, or type 2 diabetes.

A corrigendum to the paper was later published (Nutrition Research 152:171), which the journal's own record does not explain in enough detail to say what it changed; the figures above are the ones repeated consistently across the University of Reading's release and the subsequent news coverage.

The caveat that has to come first

The review was funded by the National Dairy Council in the United States and by CNIEL, the French dairy industry's trade body. Two of the paper's authors work directly for CNIEL, a third has received funding from Dairy Management Inc., and Professor Givens has received funding from multiple international dairy organizations over his career. Food writer and NYU professor Marion Nestle flagged it on her Food Politics site as an "industry-funded study of the week."

None of that means the numbers are wrong. It does mean this is a review of existing evidence, conducted and written by researchers tied to the industry whose product it is assessing, and it has not yet been independently replicated. Treat the finding as a real data point pointing toward "dairy trans fat looks different from industrial trans fat," not as a closed question.

Why the chemistry is genuinely different, not just the funding

This is the part of the story that holds up regardless of who paid for the review. Industrial trans fat is produced by partially hydrogenating vegetable oil, a process that creates a broad mix of trans-fat isomers. The trans fat in dairy and beef is made by an entirely different route: bacteria in the stomachs of cows, sheep and other ruminant animals partially hydrogenate the fat in what the animal eats, a process called biohydrogenation. The dominant product of that process is a single compound, vaccenic acid (trans-11 18:1), which the body also converts in small amounts into conjugated linoleic acid, a fat that has been separately studied for potential health benefits rather than harms.

That is why the FDA's 2015 determination, which found that partially hydrogenated oils are no longer "generally recognized as safe," applies specifically to that industrial process. The agency's own rule explicitly does not reach naturally occurring trans fat from ruminant sources. Dairy and beef have been exempt from the regulatory crackdown the whole time, not because regulators overlooked them, but because the chemistry was understood to be different from the start. This review is an attempt to test whether the health outcomes bear that distinction out, and on the evidence pooled here, they do.

One nuance worth keeping: not every trans fat made by rumen bacteria is this same reassuring story. A different ruminant-derived isomer, trans-10 18:1, has been flagged in some research as behaving more like industrial trans fat. This review's conclusions are about the dairy trans fat pool as a whole and the two compounds it specifically tracked, not a blanket statement that every trans-fat molecule a cow produces is automatically fine.

What foods actually carry it

Precise per-serving figures for vaccenic acid are not available the way they are for a vitamin, because food composition databases generally report total trans fat rather than breaking out the ruminant-derived kind, and the amount in any dairy or beef product shifts with how much fat the animal's diet contained (grass-fed animals produce meaningfully more than grain-fed ones). What is well established is the ranking:

• Butter, the most concentrated source, since it is almost entirely dairy fat
• Cream and full-fat cream products
• Cheese, hard and aged cheeses generally carrying more than fresh, low-fat cheeses
• Whole milk, more than reduced-fat or skim, because the trans fat travels with the milk fat
• Yogurt made from whole milk, more than fat-free yogurt
• Beef and lamb fat, including the fat in ground beef, roasts and lamb chops
• Low-fat and skim dairy, carrying a fraction of what the full-fat version of the same product does
• Poultry, fish, eggs and plant foods, carrying essentially none, since the biohydrogenation that produces it is specific to ruminant digestion

The one number from this review that is reliable is a whole-diet figure, not a per-food one: the trial diets that tested dairy trans fat intake spanned 1.3 to 13.2 grams a day, which gives a sense of the range a realistic diet heavy in full-fat dairy can reach.

Is there a recommended amount?

No official body sets a recommended intake for dairy trans fat specifically, and this review does not propose one. The only trans-fat number in wide circulation is the American Heart Association's longstanding advice to keep total trans fat, from any source, under 1% of daily calories, about 2 grams on a 2,000-calorie diet. That guidance predates this review and was built around the industrial kind; whether it should be read differently for the dairy-derived kind is exactly the question this review raises without settling.

Too little, and too much

Too little is not a meaningful category. Dairy trans fat has no known required function in the body, and nobody is at risk from eating none of it.

Too much is where industrial and natural trans fat still diverge sharply in the evidence. For industrial trans fat, the case is not in dispute: the World Health Organization estimates it causes roughly 500,000 deaths a year worldwide from coronary heart disease, which is why WHO has pushed for its global elimination since 2018 and why the US effectively removed it from the food supply by 2018. For the dairy-derived kind specifically, this review found no comparable signal across 22 studies, but one review, funded by the product's own industry, is not the same evidentiary weight as two decades of research on the industrial kind. The honest summary: there is real reason to think dairy trans fat is not the same hazard, and not yet enough independent evidence to say the question is closed.

Tracking it in AIM

AIM does not track trans fat, industrial or dairy-derived, as standard, so add it as a custom metric if you want to watch it: give it a name, a unit (g), and either no target or the AHA's roughly 2 g per day ceiling if you want one to log against. Any custom nutrient works the same way.

Worth being direct about a limit here: a nutrition facts label lists total trans fat without separating the industrial kind from the dairy kind, and a photograph cannot do that separation either. Watching total trans fat is a reasonable proxy for cutting back on the only kind with an established, undisputed case against it, industrial trans fat, since fried and packaged foods are still where most of it comes from. It is not a way to isolate vaccenic acid specifically. Estimates from a photograph carry real uncertainty for any micronutrient-level figure, because content varies with the animal's diet, the cut and the preparation in ways no image contains. Treat the week as meaningful and any single day as approximate.