Low-fat dairy products may not be healthier than full-fat, researchers say, challenging decades of common knowledge linking full-fat dairy to weight gain and cardiovascular conditions.

For decades, scientists and nutritionists preached switching to low-fat dairy to counter obesity and cholesterol, but new research suggests otherwise and goes a step further to indicate that, instead, a full-fat dairy serving could even offer some health benefits.

Research by Harvey Anderson, professor at the University of Toronto, adds to growing evidence that full-fat dairy can be part of a healthy diet.

The researchers found that eating three servings of full-fat dairy per day did not negatively affect body weight, body composition, energy metabolism, or blood lipid levels, as per a report published in The Journal of Nutrition.

So, what did the research find and how? And does low-fat make any difference?

What does the study show?

The researchers at the University of Toronto assigned 74 adults with overweight or obesity to one of three dietary groups, studied between September 2020 and February 2023.

One group followed a low-dairy, calorie-restricted diet; the second group followed an energy-neutral diet with three servings of dairy each day; the third group ate an unrestricted diet with three daily servings of dairy. Those assigned to the dairy groups were supplied with full-fat dairy products during the study.

After 12 weeks, researchers found no meaningful differences in weight gain, body composition, or cholesterol levels between people following the low-dairy diet and those eating three servings of dairy each day.

The research cites food guides in Canada and the United States recommending three servings of low- or no-fat dairy a day for adults, noting that the countries are not recognising recent evidence that full-fat dairy may be beneficial.

The study found that participants consuming more dairy showed improvements in blood pressure and better intake of calcium, protein and vitamin D.

“Those that had three servings of dairy didn’t have adverse levels of blood cholesterol or lipids or evidence of insulin resistance,” Anderson told the ScienceDaily website.

Why has full-fat dairy been frowned upon?

The basic nutritional logic has been straightforward: whole-fat dairy contains substantial saturated fat, and saturated fat raises LDL cholesterol, known as “bad cholesterol”; therefore, cutting the fat content of dairy should reduce cardiovascular risk.

Dietary guidance treated saturated fat as a major health risk and encouraged people to switch from whole milk and other full-fat dairy to low-fat or fat-free versions.

The underlying logic was not entirely wrong. Saturated fat raises cholesterol, and replacing saturated fat with unsaturated fats, particularly polyunsaturated fats found in foods such as nuts, seeds and vegetable oils, is associated with lower cardiovascular risk.

However, a large Harvard analysis published in 2016, involving more than 220,000 participants across three US cohorts, found that dairy fat itself was not associated with higher cardiovascular disease risk, but replacing dairy fat with polyunsaturated fat was associated with a 24 percent lower cardiovascular risk, while replacing it with vegetable fat was associated with a 10 percent lower risk.

Prof Anderson, who led the latest research, said the evidence from human research has not always matched those concerns. Some studies, including recent research led by Temerty Medicine professor Kozeta Milliku, have even reported positive or protective effects associated with dairy consumption, he noted.

How does new research counter it?

Existing popular understanding suggests that removing dairy fat was expected to help prevent excess weight gain. The new study complicates this assumption.

If three servings of full-fat dairy per day do not cause measurable increases in weight, body fat, or cholesterol, it suggests that the presence of dairy fat in a person’s diet does not automatically translate into the adverse metabolic effects that the old model predicted.

It also challenges the idea that the fat content printed on the dairy label is, by itself, a useful proxy for the food’s health effects.

However, the bigger question it posed was for the food matrix itself.

Older nutritional thinking often focused on individual nutrients: saturated fat was considered a risk factor, so a food containing more saturated fat was presumed to be worse.

But researchers are increasingly looking at dairy as a whole food matrix containing protein, minerals, vitamins, carbohydrates and fat. The way those components interact may affect how the body responds to the fat.

In simpler words, the health effects of a food may depend on how its components interact rather than simply on the amount of one nutrient it contains.

“With dairy products, it’s got two proteins – casein and whey – that are bound together with fat and with nutrients mixed in,” says Anderson.