The study of Dehghan et al. (2017) “Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study” 1 is a part of a large-scale epidemiological study Prospective Urban Rural Epidemiology (PURE), which an ultimate aim was to examine the relationship between societal influences, lifestyle behavior, and cardiovascular risks in human population 2. In the recent study, Dehghan et al. (2017) examine the association between carbohydrate and fat consumption with cardiovascular risks and related mortality. The study included about 135 000 individuals aged 35-70 years in 18 countries on 5 continents followed for 7.4 years on average. The general conclusion of the study is that high carbohydrate consumption, but not total fat or different types of fat, were associated with higher cardiovascular risks. For these reasons, the authors propose that current “dietary guidelines should be reconsidered” 1. Although the study has a few weaknesses, being one of the largest observational studies to the association between nutrition and cardiovascular risks, it can significantly contribute to the future public health measures and studies.
To better understand the relation between nutrition and the burden of cardiovascular diseases in low- and middle-income countries, the authors searched for relevant articles in PubMed in the last 50 years. Justifying their study by the lack of evidence about the association between nutrition and cardiovascular risks on a global scale, with most of the studies from European and North American countries, the authors included 18 countries classified as high-income, middle-income, and low-income countries and measured a number of parameters to strengthen the study. By now, it is one of the most comprehensive studies pointing out that high carbohydrate intake is harmful while total fats, as well as saturated and unsaturated fatty acids, have no adverse effects on mortality related to cardiovascular diseases.
The study included more than 130 000 participants in different countries. Information about demographic factors, socio-economic status, lifestyle, health history, physical activity, and food intake was collected using questionnaires at the individual levels, household, and community. Even though dealing with this number of participants, they succeed to overcome some methodological problems. For instance, for those countries that did not have questionnaires available, new ones were developed using a standard method. They also adjusted models for sex, gender, and education and categorized countries into seven regions due to different culture-dependent dietary patterns. Furthermore, they maximize the significance of the results within regions by taking into consideration the differences in food intake that might occur, such as the difference in carbohydrate intake between Asian and non-Asian countries, with higher intake in Asian countries. Based on the nutrition intake, they even categorized participants into region-specific categories.
The results of this comprehensive study are clearly presented especially considering the number of countries involved, number of participants with wide variability in diet, lifestyles, and disease incidence, different parameters measured, and the time period of the study. The main results clearly state that higher carbohydrate intake is associated with an increased risk of cardiovascular risks and mortality unlike higher total fat and/or different types of fat, which were not associated with cardiovascular risks and mortality. Consequently, their results do not support the recommended guidelines of total fat and saturated fat intake proposed by the World Health Organization (2018) 3 and suggest the revision of current dietary guidelines. This, however, opens a lot of questions since a single study, even with impressive numbers of participants and researchers involved such as the reviewed one, is not enough to change global guidelines.
Despite being a large and detailed study, a few weaknesses can be observed and some of them are even noted by the authors themselves. Namely, the food frequency questionnaires used for the study did not measure absolute intake and the nutrient database used for these questionnaires was not the same for all the countries with most of them based on the United States Department of Agriculture food composition database. Further, food intake was measured only at baseline and possible changes in dietary habits or lifestyles were not taken into consideration. For the latter one, the authors did not expect to affect the results although daily lifestyle habits are associated with cardiovascular risks 4, 5. As authors also mentioned, they were unable to quantify different types of carbohydrate and to measure trans-fat intake. Despite the fact they proposed ApoliproteinB-to-ApoliproteinA1 ratio as strong lipid predictor of cardiovascular risk, the measurements of the ratio were not observed in this article, though the results are presented in the associated article 6 from the PURE study. One of the limitations of the study is using questionnaires in data collection since questionnaires may not be very accurate as they depend on subjective interpretation, which could affect the assessment of the real association between nutrients and cardiovascular risks. Yet, they are still commonly used in studies with a great number of participants. As Ramsden and Domenichiello (2017) point out, it seems that there are a lot of questions open for the future research. They suggest further research that will observe the effects of different animal products rich in saturated and unsaturated fatty acids, micronutrient deficiency, and different types of carbohydrates (refined sugar or whole grain) intake on cardiovascular risks and mortality 7. Furthermore, the information about the dominant fat types of the food, as well as the food habits in different regions of the countries included in the study is not reported and for the future research, it may be interesting to involve this information as well.
The comprehensive study of Dehghan et al. (2017) offers valuable insights into the relationship between nutrition and cardiovascular risks. It is one the largest observational study that included more than 100 000 participants in 18 different countries and about 200 researchers. Together with the associate study 6, its results will certainly contribute to the public health and maybe even influence the current dietary guidelines. Still, future research on this topic is necessary and the authors themselves are aware of some of the weaknesses and limitation of their study. Overall, this is one impressive large-scale study that opens a lot of questions about the effects of macronutrients in chronic diseases. It should incite further research in this area and include more countries and more relevant parameters, especially before reconsidering the global dietary guidelines as proposed by the authors.