- The 2025-2030 Dietary Guidelines for Americans now list full-fat dairy as a healthy fat source, reversing decades of skim-only advice.
- A 12-week University of Toronto trial found three daily servings of full-fat dairy did not increase body weight, body fat, or cholesterol in 74 overweight adults.
- The "dairy matrix" theory suggests fat behaves differently within whole dairy foods than as an isolated nutrient.
- No large-scale trial has ever directly compared full-fat versus low-fat dairy for heart attack or death outcomes.
- The longstanding 10% saturated fat cap remains unchanged, with critics calling it arbitrary and unsupported by evidence.
The policy shift that changed everything
For decades, Americans were told to reach for skim milk. In January, Washington changed its mind.
The 2025-2030 Dietary Guidelines for Americans, released Jan. 7, list full-fat dairy among whole foods that supply healthy fats and name butter among suitable cooking fats. Earlier editions favored fat-free and low-fat dairy exclusively. The shift follows mounting evidence that the old advice—rooted in 1960s-era assumptions about saturated fat—was never properly tested against the alternative.
But the guidelines did not give full-fat dairy a free pass. They still tell people to keep saturated fat below 10 percent of daily calories, or about 22 grams on a 2,000-calorie diet. Three cups of whole milk supply about 14 grams.
The comparison that was never run
Benoît Lamarche, scientific director of the NUTRISS Centre at Université Laval's Institute of Nutrition and Functional Foods, objects to the old advice not because low-fat dairy was harmful, but because the comparison was never properly made.
Few studies have compared the two directly, and those that have show the same effect either way. The reason is practical: Trials long enough to measure heart attacks would need thousands of people followed for years, while about six weeks is the realistic limit for keeping people on a controlled diet. The federal advisory committee graded the evidence as limited, and the American Heart Association said the data were inadequate to draw conclusions about blood lipids, blood pressure, or cardiovascular death.
A new trial weighs in
In January, University of Toronto researchers published a 12-week trial in The Journal of Nutrition. Adults who ate three daily servings of full-fat dairy showed no meaningful increase in body weight, body fat, or blood cholesterol compared with those eating less. Blood pressure improved.
It is a real result, albeit a small one—with only 74 overweight adults. The trial was funded by the Canadian Dairy Research Cluster 3, a joint government and industry initiative, and the Mitacs Accelerate program.
A 12-week trial can rule out obvious short-term harm; it cannot show what happens over the decades in which heart disease develops. Harvey Anderson, the University of Toronto nutritional sciences professor who led the work, framed the takeaway modestly: Keep it simple, eat a variety of foods and not too much of anything.
Why the food may matter more than the fat
The idea behind the shift is called the "dairy matrix": the theory that fat behaves differently inside a whole food than on its own.
The starting point is undisputed. Saturated fat raises LDL cholesterol, and LDL contributes to the plaque that narrows arteries. The dispute is whether saturated fat behaves the same way inside a complex food as it does as an isolated nutrient.
The clearest test has been cheese against butter. When the two are matched for saturated fat, every randomized trial to date has found that cheese produces lower LDL cholesterol, according to Emma Feeney, an assistant professor at University College Dublin's Institute of Food and Health.
Feeney described two possible explanations. The calcium in cheese forms insoluble soaps with fat in the gut, blocking some of its absorption, and cheese retains more of the milk fat globule membrane, a thin layer of bioactive compounds that may also play a role.
The cap that remains unexplained
The same document that welcomed butter back kept the ceiling that constrains it. The threshold itself has never been well explained. Lamarche said no one can explain where the 10 percent cap comes from, calling it arbitrary.
An international expert panel convened in Amsterdam in 2024 concluded that milk, yogurt and cheese are neutrally associated with cardiovascular risk regardless of fat content. Neutral is not the same as protective.
The evidence no longer supports singling out dairy fat as uniquely harmful. Nor does it establish that dairy fat is uniquely beneficial—and the two claims are easy to confuse. Feeney said she would not like anyone to take away from this research that butter is a healthier fat than any other cooking fat.
What remains unsettled is whether the matrix effect holds over decades and whether it holds for butter. The trials that would answer it have not been run.
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