On Sep 22, 2021, CNN published an article: People Who Eat More Dairy Fat Have Lower Risk of Heart Disease, Study Suggests. This click-bait title hooked us, and we scanned the article, waiting for the catch. As expected, the title is erroneously blown out of proportion—please don’t start shoveling full-fat Greek yogurt into your mouth to prevent a heart attack. We had our scientist take a look at the study that prompted this overblown CNN headline, and we found some major flaws. Here’s what the study claims, where it goes wrong, and why it still isn’t a good idea to incorporate dairy into any diet.
The Study
Published in the PLOS Medicine Journal in 2021, the study—Biomarkers of Dairy Fat Intake, Incident Cardiovascular Disease, and All-Cause Mortality—set out to learn more about the associations between dairy fat intake and one’s risk of heart disease. The researchers conducted their own cohort study of 4,150 Swedish adult participants, produced a systematic review, and conducted a meta-analysis of 18 other studies to support their findings. The goal was to challenge the assumption that all saturated fats negatively impacted LDL cholesterol and consequently increase one’s risk of heart disease.
To analyze the amount of dairy-based saturated fat in each participant, fasting blood tests were drawn and researchers specifically looked at the levels of fatty acids—pentadecanoic acid, among others—that are highly associated with dairy foods. Based on this single blood draw and participants’ dietary recall, the authors concluded that increased levels of dairy fat intake were associated with lower rates of cardiovascular disease. The result was a mere correlation. To be clear, the evidence did not suggest any causation between increased dairy fat intake and reduced risk of heart disease.
The Flaws
Several factors within this study are enough to raise our eyebrows and seriously question the validity of its conclusion. For this section, we are focusing on the cohort study.
The initial age of the participants is concerning. While individuals with known heart disease were exempt from the study, this is an illness that can go undetected for some time. According to the American Heart Association, 40 percent of men and 30 percent of women have already developed some sort of cardiovascular disease by the age of 60. If over a third of participants potentially had heart disease upon entering the study, the research doesn’t do what it intended—it’s not analyzing the role saturated dairy fat may have in delaying CVD onset, because many of the participants already had it—they just weren’t showing symptoms.
The single sample to measure select fatty acids is also a major red flag. One fleeting point in time is not significant enough to draw conclusions. Esteemed researcher and physician, Dr. Michael Klaper, says, “A lab result is hardly ever conclusive on its own. You need two points to make a line. Are things resolving or worsening?” The participants’ blood samples were used to support their dietary recall, though only markers for dairy intake were measured. There were no markers to back up the participants’ claimed consumption of fresh produce—a food group that plays a key role in cardiovascular health. Any respected researcher knows that validity is gained through multiple data points—not a shot-in-the-dark isolated sample.
What Really Reduces the Risk of Heart Disease
Based on the cohort study and systematic review, the authors of this study found a reportable correlation between increased dairy fat consumption and reduced risk of heart disease (of course, based on questionable research methods outlined above). However, they were clear in that more research is needed to connect correlation to causation: “Our findings support the need for clinical and experimental studies to elucidate the causality of these relationships and relevant biological mechanisms.” This study is not meant to dictate dietary guidelines—the authors are clear on that. Still, CNN exaggerated its findings with a headline that would fool anyone scrolling through their news feed to think dairy products are heart-healthy.
When consuming any food, one needs to look at the whole package. Yes, dairy contains calcium and protein, but it also contains cholesterol, bovine hormones, and inflammatory compounds. Due to the many flaws in this study, we can’t be certain that dairy fat is benign when it comes to heart health (in fact, there are several studies that say otherwise), but we can be certain that whole foods such as grains, legumes, fruits, and vegetables are not negatively associated with cardiovascular issues and may in fact play a role in reducing one’s risk of heart disease. Taking care of your heart isn’t complicated, and a shoddy study shouldn’t take the focus away from the benefits of plant-based food.
For more on heart health and the relative risk of heart disease, listen to our podcast with cardiologist Dr. Monica Aggarwal.
