Fat-reduced dairy products are usually recommended over whole-fat dairy products, because they contain less calories and saturated fat. However, clinical trials do not consistently show an improvement of cardiometabolic risk factors when comparing low fat dairy consumption to whole-fat or overall dairy consumption (1-3). Similarly, the possible effects of dairy fat consumption on the risk of type 2 diabetes are not well established.
Summary | Imamura et al. showed that higher biomarker levels of dairy fat consumption were associated with a 29% lower risk of type 2 diabetes. Although there is still some uncertainty about the meaning of the biomarkers, this meta-analysis suggests that dairy fat consumption is possibly associated with a lower risk for type 2 diabetes.
In observational studies, total dairy consumption has been associated with a lower risk of type 2 diabetes (5). However, the evidence is inconsistent for different types of dairy foods such as milk, yogurt and cheese (5). To provide more clarity on this topic, Imamura et al. (2018) performed a meta-analysis to assess the association between biomarkers of dairy fat consumption and the risk of type 2 diabetes. This article is a summary of this meta-analysis.
Biomarkers of dairy fat consumption
Measuring dairy consumption with the use of self-reported dietary questionnaires can be inaccurate, since this kind of method depends on the memory of participants. It may also contain other errors due to subjective reporting. To reduce these limitations and measure dairy consumption more accurately, the current meta-analysis focused on studies that measured biomarkers of dairy fat consumption.
The following saturated and trans fatty acids were considered as biomarkers for dairy fat consumption (meaning they reflect dairy fat intake): pentadecanoic acid (15:0), heptadecanoic acid (17:0) and trans-palmitoleic acid (t16:1n7). Evidence for the use of these fatty acids as biomarkers includes that 1) levels of the fatty acids correlate with self-reported consumption of total dairy, high-fat and dairy fat based on 24-hour recalls or 7-day food records 2) levels of the fatty acids significantly increase after dairy consumption and decrease after replacing high fat dairy with low fat dairy in trials and 3) the fatty acids are correlated with each other even though they represent a different class of fatty acids.
How the meta-analysis was conducted
In the meta-analysis, 16 individual observational studies were pooled together. These studies met the following criteria:
- The studies included participants of 18 years or older who were free from diabetes at the time of fatty acid assessment.
- The studies measured circulating or adipose 15:0, 17:0 or t16:1n7 (at the start of the study).
- Participants were followed up for development of type 2 diabetes.
Three statistical models were used to assess the association of dairy fat biomarker levels (each of the fatty acids separately and their sum) and the risk of type 2 diabetes. Other factors that could influence the association of dairy fat consumption and type 2 diabetes risk (confounders) were indicated, such as age, sex, BMI, dyslipidaemia and many more, and included in the statistical models. In the third model, all indicated factors were included. In this way, the risk of type 2 diabetes in relation to dairy fat consumption was calculated independently of other (risk) factors.
The biomarkers and diabetes risk
Combining the 16 individual studies, the meta-analysis included more than 60.000 participants with an average follow up of 9 years. In the third model, higher levels of fatty acids 15:0, 17:0 and t16:1n7 were associated with a 20%, 35% and 18% lower risk of type 2 diabetes, respectively. A higher sum of the three fatty acids was associated with a 29% lower risk. The effects of higher biomarker levels seem to be stronger in woman compared to men. For example, a higher total sum of the three fatty acids was associated with a 33% reduced risk for type 2 diabetes in women, while for men this was a reduced risk of 23%.
Strengths and limitations of the meta-analysis
- The meta-analysis included a large number of participants which led to a large statistical power and generalizability of the results.
- Many potential confounders were included and adjusted for in the statistical analysis.
- Biomarkers are free from memory bias, which makes them preferable over self-reporting methods.
- Although there is evidence that the used biomarkers at least partly reflect dairy fat intake, they may also be influenced by unknown factors.
- Besides, it is not yet known how much intake of dairy fat the biomarkers reflect and if they reflect short term intake or long term intake. Therefore, more research into the determinants of levels of the biomarkers is needed.
- The biomarkers cannot distinguish between different food sources of dairy fat (e.g. cheese, yoghurt or milk). Therefore, it is not possible to draw conclusions about the effect of consumption of different dairy products on the risk of type 2 diabetes.
- Since observational studies can only assess associations and not causal relationships, more research is needed into the biological mechanism that underlies the observed lower risk for type 2 diabetes. Also, the findings support the need for intervention studies on the health effects of dairy fat.
Key points from the meta-analysis
- Low fat dairy products are usually recommended over whole fat dairy products, because they contain less saturated fat. However, studies do not consistently show an improvement of cardiometabolic risk factors when comparing low fat dairy to whole-fat dairy consumption.
- Similarly, the possible effects of dairy fat consumption on the risk of type 2 diabetes are not well established.
- This meta-analysis that included 16 observational studies assessed the association of biomarkers of dairy fat consumption and the risk of type 2 diabetes.
- Higher levels of the biomarker for dairy fat consumption was associated with a 29% lower risk for type 2 diabetes.
- It is not yet clear what the effect of different dairy products (such as cheese, yoghurt or milk) on the risk of type 2 diabetes is.
- More research is needed into the exact meaning and determinants of levels of the biomarkers and into the biological mechanism that underlies the observed lower risk for type 2 diabetes.
- Lawrence, G. D. (2013). Dietary fats and health: dietary recommendations in the context of scientific evidence. Advances in nutrition, 4(3), 294-302.
- Drouin-Chartier, J. P., Côté, J. A., Labonté, M. È., Brassard, D., Tessier-Grenier, M., Desroches, S., … & Lamarche, B. (2016). Comprehensive review of the impact of dairy foods and dairy fat on cardiometabolic risk. Advances in Nutrition, 7(6), 1041-1051.
- Benatar, J. R., Sidhu, K., & Stewart, R. A. (2013). Effects of high and low fat dairy food on cardio-metabolic risk factors: a meta-analysis of randomized studies. PloS one, 8(10), e76480.
- Imamura, F., Fretts, A., Marklund, M., Korat, A. V. A., Yang, W. S., Lankinen, M., … & Bassett, J. K. (2018). Fatty acid biomarkers of dairy fat consumption and incidence of type 2 diabetes: A pooled analysis of prospective cohort studies. PLoS medicine, 15 (10), e1002670.
- Gijsbers, L., Ding, E. L., Malik, V. S., de Goede, J., Geleijnse, J. M., & Soedamah-Muthu, S. S. (2016). Consumption of dairy foods and diabetes incidence: a dose-response meta-analysis of observational studies. The American journal of clinical nutrition, 103(4), 1111-1124.