In our latest interview, we spoke to Dr. Kathy Trieu from The George Institute for Global Health in the Food Policy Division about the impact of dairy fats on cardiovascular disease.
What provoked your latest research into dairy fats and cardiovascular disease?
We undertook this study on dairy fats and cardiovascular disease because there was increasing evidence to suggest that the health impact of dairy foods is more dependent on the type – such as cheese, yogurt, milk, and butter - rather than just the fat content. This raised doubts about whether the avoidance of dairy fats overall is beneficial for heart health.
A better understanding of the link between dairy fats and cardiovascular disease is important because dairy foods are being increasingly consumed worldwide and are a major source of nutrients.
What research has been carried out so far into cardiovascular disease and diet?
There is extensive evidence from randomized trials, epidemiological studies, population studies, and animal studies that all suggest a clear link between dietary habits and cardiovascular disease. These research findings have been widely used to inform national and international dietary guidelines aimed at preventing chronic diseases.
The Global Burden of Disease Study estimated that one of every three cardiovascular disease deaths worldwide were attributed to poor diets in 2019.
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What is dairy and what foods typically have dairy fats in them?
Dairy foods are any foods made from the milk product of animals, usually cow’s milk, although some are from the milk of sheep, goats, and other animals. Common dairy foods include milk, yogurt, cheese, butter, and cream and they contain varying levels of dairy fat.
Why do some dietary guidelines suggest that consumers choose low-dairy products?
Most dietary guidelines advise consumers to choose low-fat dairy products due to the high content of saturated fats and calories in full-fat dairy options. Increased intake of saturated fat can increase the ‘bad’ blood cholesterol (LDL) and the risk of cardiovascular disease.
However, increasing research shows that although dairy products can be rich in saturated fats, they are rich in other nutrients and can be part of a healthy diet. There is also more evidence suggesting that some dairy foods like yogurt and cheese can have more health benefits than others, like butter.
While most dietary guidelines continue to recommend low-fat dairy, others focus less on the fat content and rather on the type of dairy and the avoidance of sweetened products like flavored milks and yogurts.
Why could this information be potentially harmful?
There is good evidence to recommend unsweetened low-fat dairy, but there is more uncertainty about the health effects of full-fat dairy.
Recommendations to avoid dairy fat may be potentially harmful as consumers may select low-fat dairy options that are instead loaded with sugar. Eating too much sugar is known to be harmful, leading to weight gain, cardiovascular disease, diabetes, and tooth decay.
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Can you describe how you carried out your latest research into dairy fats and cardiovascular disease?
Our research involved measuring dairy fat consumption in over 4,000 Swedish adults based on blood levels of a particular fatty acid (called pentadecanoic acid 15:0) that is mainly found in dairy foods. The participants were then followed up for an average of 16 years to see how many had heart attacks, strokes, and other serious circulatory events, and how many died from any cause during this time.
In addition, we searched for all previously published studies that investigated the link between blood levels of fatty acids that reflect dairy fat consumption and cardiovascular disease or death, so that we could combine the findings and summarise all the evidence to date.
What did you discover?
In the Swedish study, after statistically adjusting for other known cardiovascular disease risk factors including things like age, education, lifestyle, dietary habits, and other diseases, the cardiovascular disease risk was lowest for those with high levels of the fatty acid (reflecting high intake of dairy fats). Those with the highest levels had no increased risk of death from all causes.
Combining these results with 17 other studies, involving a total of almost 43,000 people from the US, Denmark, and the UK confirmed the link between higher levels of these fatty acids, reflecting higher dairy fat intake, and lower risk of cardiovascular disease. These results are highly interesting but should be interpreted with caution.
We cannot determine any causality or mechanisms of the observed associations. As with any observational study, there is also a possibility that other lifestyle factors could have impacted the associations, despite our attempts to statistically control for these. However, our findings do not suggest any harm from dairy fat per se.
Many studies have relied upon people remembering the amounts and types of dairy foods that they have eaten. What are the limitations of this? How did your study differ?
Many studies that measure dairy fat consumption by asking people to remember and recall what they have eaten have several limitations.
Firstly, they rely on participants honestly reporting what and how much was eaten, although research shows people tend to report what is viewed as socially desirable, e.g. healthier foods or smaller amounts of unhealthy foods compared to what was actually consumed.
Secondly, they rely on the participant’s memory to recall and report all the food and beverages consumed (including whether they were low-fat or full-fat products) and the amount. This is particularly challenging when quantifying dairy fat intake because dairy is often incorporated in mixed dishes and therefore the quantity is difficult to estimate or can be forgotten, for example, cheese sprinkled on dishes or butter and cream used in cooking.
Thirdly, the recalled food intakes need to be matched up with data on the nutrient composition (i.e. dairy fat content) of the foods to estimate the amount of dairy fat consumed which is not always available or may be outdated, inaccurate, and not brand-specific.
Our study overcomes these limitations through objectively measuring blood levels of certain fatty acids that mostly come from dairy foods, thereby acting as a marker for dairy fat intake. However, despite the many advantages of using fatty acids as objective markers, there are some limitations. For example, we were unable to investigate associations of different dairy foods (like yogurt vs butter) with health outcomes and the levels of these fatty acids can be influenced by other factors than just intake of dairy fat.
What further research needs to be carried out to fully understand the health impact of dairy fats and foods?
Further research is needed to confirm that a higher intake of dairy fat causes lower cardiovascular disease risk. Our study currently shows there is an association between dairy fat and cardiovascular disease risk, but we do not have evidence that dairy fat per se causes this lower disease risk.
Similarly, more research is needed to understand the biological mechanism behind the observed link between dairy fat and cardiovascular disease, i.e. what nutrients or properties within dairy foods or dairy fats are lowering cardiovascular risk.
What are the next steps for your research?
To better understand these findings we need well-designed randomized controlled trials to investigate the health benefits of different types of dairy foods and to compare the effects of low-fat vs full-fat dairy foods.
Where can readers find more information?
About Dr. Kathy Trieu
Dr. Kathy Trieu is a Research Fellow at The George Institute for Global Health in the Food Policy Division. She is also a conjoint senior lecturer at the University of New South Wales. Her research is supported by an Early Career Fellowship from the National Health and Medical Research Council of Australia, and the National Heart Foundation of Australia.
Kathy completed her Ph.D. in the implementation and evaluation of population strategies to lower salt intake for the prevention of hypertension and cardiovascular disease at the University of Sydney. She also holds a Master of Public Health and a Bachelor of Applied Science in Nutrition degree from The University of Sydney.
Kathy’s research focuses on investigating diet-related causes of noncommunicable diseases; designing, implementing, and evaluating nutrition interventions; and influencing nutrition policies through modeling and evaluations. So far Kathy has worked with local academics, governments, and non-governmental organizations on nutrition and food-related research in 10 countries. Her research aspirations involve undertaking high-quality research that can usefully inform effective programs and policies to improve population-wide nutrition and health in countries around the world.