A New Study Adds to the Debate Over Dairy

Highlights: 
  • The Dietary Guidelines for Americans recommend choosing low- and non-fat dairy products based on the saturated fat content of whole-fat dairy, which has been associated with increased LDL (“bad”) cholesterol. However, this topic has recently been debated within the nutrition community.
  • This observational study found that intake of whole- and low-fat dairy (more than 2 servings per day) was associated with a reduction in the risk of major cardiovascular events and mortality.
  • Though the results of this study are strengthened by its large and diverse sample size, there are limitations such as a restricted collection of dietary intake data and its observational study design. This type of study cannot provide direct evidence that consuming dairy products prevents cardiovascular disease or mortality.

A new study published in The Lancet is hot off the presses, and the results may surprise you: Higher intake of total dairy (more than two servings of dairy per day) was associated with lower risk for mortality and cardiovascular disease. But what do these findings mean for you? Should you make the switch from skim to whole milk? We’ve assessed the study and put the findings into perspective. Read on to get our take.

Why Was This Study Done?

The purpose of this study was to assess any associations between total dairy and specific types of dairy products with mortality and major cardiovascular disease.

This research adds to a hot debate in the nutrition community, with some research showing that reducing saturated fat reduces cardiovascular risk and other research showing the opposite. Moreover, whole-fat dairy products are not currently recommended by the Dietary Guidelines for Americans.

Methods

This research was part of the Prospective Urban Rural Epidemiology (PURE) study, a large multinational cohort study of 136,384 individuals aged 35–70 years from 21 countries on five continents. It’s one of the most diverse observational studies done to date. In fact, we’ve written about a previous study from this cohort before.

Intake of full-fat and low-fat dairy products (defined as milk, yogurt, yogurt drinks, cheese and mixed dishes prepared with dairy) was assessed using a single country-specific food frequency questionnaire (FFQ) at the beginning of the study. Participants were asked how often they had consumed specific foods and drinks on average in the past year, and the dairy products were classified as either low-fat or full-fat. Butter intake was not measured in some of the FFQs, and cream and ice cream were not included in the published analysis, as far as we could see.

From this information, participants were grouped into four categories: no dairy (28,674 people), less than one serving per day (55,651), one to two servings per day (24,423) and more than two servings per day (27,636). Study participants were followed for about nine years before the results were assessed.

Results

Dairy consumption was associated with a lower risk of cardiovascular disease and death. Compared to people who didn’t eat dairy, those who consumed more than two servings per day had lower total mortality rates (3.4 percent versus 5.6 percent), decreased risk of major cardiovascular disease (3.5 percent versus 4.9 percent), and decreased risk for stroke (1.2 percent versus 2.9 percent).

Among people who ate only full-fat dairy, those who consumed about three servings per day had slightly lower mortality rates than people who ate less than half a serving per day (3.3 percent versus 4.4 percent), and a similar pattern was seen for cardiovascular disease (3.7 percent versus 5.0 percent). No statistically significant differences in mortality or cardiovascular disease risk were seen when it came to low-fat dairy. Higher intake of saturated fats from dairy was not associated with total mortality or major cardiovascular disease.

Strengths and Limitations

There’s no denying that this study had a very large and diverse sample size. This might be the first of its kind to look at dairy consumption and cardiovascular disease in such a wide range of countries. But despite these strengths, it remains an observational study, a type of study design that has a great deal of limitations. We’ve written about these points before, but importantly, observational studies cannot prove cause and effect—that is, we can’t conclude that eating more dairy prevents people from dying or having a heart attack.

Also, even though the study controlled for several health and environmental factors such as age, education, smoking status, family history and dietary intake of fruit, vegetables, red meat and starchy foods, there may be other confounding variables that differentiate people who are willing and able to consume more dairy in these areas versus those who will not or cannot. For example, people with more expendable income may be able to buy these foods, while lower income people cannot. Notably, individual income was not included in the statistical models that aim to account for potential confounding factors; instead, specific countries were described as “low-”, “middle-” or “high-income”.

Another major pitfall was that the study only measured what participants consumed only at one point in time and didn’t conduct any follow-up measurements of dietary intake, so it’s impossible to tell if the participants changed their diet habits over time. The authors of the study acknowledged this point and highlighted one of the common downsides of observational studies: Following up with participants is time-consuming, labor-intensive and expensive, which makes continual information collection difficult, if not impossible.

Putting the Study into Context

So after all of this, you’re probably still wondering which kind of yogurt to put in your grocery cart. And the answer is, well, complicated. As we mentioned, the Dietary Guidelines recommend low- or non-fat dairy, and that’s usually the standard that we look to for advice. However, full-fat dairy products have recently picked up steam in nutrition circles and research like this indicates that they may not be as “bad” for us as we’ve traditionally thought.

In The New York Times, the study’s lead author notes that current dietary guidelines are based on the presumed harms of saturated fatty acids on a single risk marker, LDL cholesterol. But dairy products include many different nutrients, including protein and calcium. Singling out one nutrient as “bad” or “good” while not considering the full nutrient profile of the food has historically produced unexpected, and sometimes harmful, results.

Until we know more about how saturated fat from dairy products affects our health, it’s important to choose dairy foods that you like, while considering calorie and fat intake and talking with your healthcare provider if you have concerns. They’ll be able to take that information and apply it in the context of, say, your LDL levels and determine if any dietary adjustments could or should be made.

There’s no doubt that this debate isn’t over, and you can bet we’ll be ready to talk it through with you in the future.

This blog includes contributions from Alyssa Ardolino, RD, and Megan Meyer, PhD.

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