Wuhan, China — On March 6th, Professor Pan An from the School of Publish Health, HUST, and colleagues were invited to write a review on Cell Metabolism, a leading biomedical journal in the field of metabolism with an impact factor of 20.565.
This review discussed the association between diet and cardiovascular health from the perspective of epidemiologists, reviewed recent epidemiological studies on dietary patterns and cardiovascular health, and pointed out the possible methodological issues in a recent study from the Prospective Urban and Rural Epidemiology (PURE) cohort.
Cardiovascular disease, particularly coronary heart disease and stroke, is the leading cause of disability-adjusted life years and death all over the world. During the past few decades, a large number of studies have broadened people’s understanding of the association between diet and cardiovascular health in a great detail.
Divergent results, however, have often caused confusion among patients, health professionals, scientists, policy makers and the general public. For instance, the PURE study demonstrated the relationship between macronutrient intake and mortality via analyzing self-reported dietary data from more than 135,000 participants from 18 countries, including China, in a follow-up of 7 years. The study concluded that “high carbohydrate intake was associated with higher risk of total mortality, whereas total fat and individual types of fat were related to lower total mortality.” This article has caused intense discussions in the scientific community and misinterpretation and reprinting of many media, since its publication on Lancet in September 2017. Specifically in China, due to the high level of carbohydrate consumption in the traditional diet pattern, it received more attention.
Carbohydrates are found in a variety of foods and are the main source of daily energy intake for most people. The traditional classification relying on polymerization and chemical structure – monosaccharides, oligosaccharides and polysaccharides – could not distinguish the quality of carbohydrates and impacts on health. Recent studies have increasingly focused on glycaemic index and glycaemic load, the amount and type of dietary fibres, and the degree of food processing. Numerous studies have increasingly shown that high-quality carbohydrate intake, for example lower glycaemic index and glycaemic load, lower sugar-sweetened beverages and added sugars, more dietary fibre and whole grains, can significantly reduce the risk of type 2 diabetes and cardiovascular disease.
On the aspect of fat consumption, the latest 2015-2020 Dietary Guidelines for Americans has eliminated the previous upper limit for total fat intake, but focused on the different types of fat, instead. A series of studies have confirmed that replacing saturated fats with polyunsaturated or monounsaturated fats can significantly reduce the risk of cardiovascular disease. The use of refined carbohydrates (such as refined starch, white rice, added sugars, etc.) instead of saturated fat did not significantly reduce the risk of cardiovascular diseases, which also suggested that refined carbohydrates and saturated fat have no significant difference in cardiovascular health.
In the PURE study, the researchers did not distinguish the types of carbohydrates. It is obviously not reasonable to mix low and high quality carbohydrates together. People living in numbers of the developing countries included in the PURE study, suffer from poverty and food shortage and consume a “poverty diet”, which contains many refined carbohydrates, such as white rice and refined wheat products, whereas the amount of fruit and vegetables, high quality protein and fat is remarkably low. Moreover, their health awareness or medical service was low. Therefore, the correlation between high carbohydrate consumption and high mortality observed in the PURE study largely reflected the relationship between poverty-related factors and death. This emphersized the importance of paying attention to confounding factors in epidemiological studies.
On the other hand, one-third of the participants in the PURE study came from China, but their dietary intake data were questionable. National surveys reported that the Chinese population has consumed an average of 30% of their daily calories from fat since 2002, and in some metropolitans the proportion is almost 40%. Nevertheless, the total fat intake in the PURE study was only 17.7%, which casts doubt on the validity of the study’s dietary assessment procedures. So far, the study authors have not responded to data quality publicly.
In the past decades, nutritional epidemiology has formed its own unique series of practical and theoretical principles, and its latest developments have increasingly emphasized the essence of the holistic dietary patterns. For instance, a large number of prospective cohort studies and some clinical trials have shown that the Mediterranean diet, DASH diet and AHEI diet can reduce the risk of cardiovascular disease. With the popularization of genomics and other multi-omics technologies such as metabonomics, the development of the “precision nutrition” will be promoted greatly further via applying multi-omics methods to large cohort studies and combining with some new dietary measurement methods and dynamic observations such as repeated measurements by the wearable devices.
Professor Pan An and his colleagues underlined that it is the quality of the dietary and the sources of different nutrients (such as fat and carbohydrates) that should be highlighted rather than the quantity. Although the recommendation of food categories from different dietary patterns differs from one another, healthy dietary patterns are generally rich in whole grains, vegetables, fruits, fish, legume and nuts, moderate amounts of low-fat or skim dairy, whereas the consumption of red meat, processed meat, refined grains, sugar-added foods and beverages is as little as possible.
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For more details of the paper, please visit: https://doi.org/10.1016/j.cmet.2018.02.017
