Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study
The relationship between the roles of fat intake and different fatty acids in the onset of cardiovascular disease (CVD) and mortality is controversial. Newly posted under the “Cardiovascular Disease” section are the results of the Prospective Urban Rural Epidemiology (PURE) study (1). The PURE study is a large, epidemiological cohort study of individuals aged 35–70 years (enrolled between Jan 1, 2003, and March 31, 2013) in 18 countries with a median follow-up of 7·4 years (IQR 5·3–9·3). Dietary intake of 135,335 individuals was recorded using validated food frequency questionnaires. The primary outcomes were total mortality and major cardiovascular events (fatal cardiovascular disease, non-fatal myocardial infarction, stroke, and heart failure). Secondary outcomes were all myocardial infarctions, stroke, cardiovascular disease mortality, and non-cardiovascular disease mortality
During follow-up, 5796 deaths and 4784 major CVD events were recorded. 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. Total fat and types of fat were not associated with cardiovascular disease, myocardial infarction, or cardiovascular disease mortality, whereas saturated fat had an inverse association with stroke.
This is one of the most comprehensive studies to date to examine how diet affects health and mortality. The data from the PURE study shows that rather than lowering fat, more people might benefit from lowering the amount of carbohydrates they eat. The data suggested that those who ate high quantities of carbohydrates, which are found in breads and rice, had a nearly 30% higher risk of dying during the study than people eating a low-carb diet. And people eating high-fat diets had a 23% lower chance of dying during the study’s seven years of follow-up compared to people who ate less fat. The results point to the fact that rather than focusing on fat, health experts should be advising people to lower the amount of carbohydrates they eat. In the study, which involved 135,000 people from 18 different countries, the average diet was made up of 61% carbohydrates, 23% fat and 15% protein. In some countries, like China, south Asia and Africa, however, the amount of carbohydrates in the diet was much higher, at 63% to 67%. More than half of the people in the study consumed high-carbohydrate diets.
The researchers also examined the impact of fats and carbohydrates on blood lipids in the same PURE study participants. Consistent with other reports from Western countries, they found that while LDL (so-called “bad” cholesterol) increases with higher intakes of saturated fat, HDL (“good” cholesterol) also increases – so the net effect is a decrease in the total cholesterol/HDL ratio. They found that LDL cholesterol (the basis of many dietary guidelines) is not reliable in predicting effects of saturated fat on future cardiovascular events. Instead, ApoB/ApoA1 provides the best overall indication of effect of saturated fat on cardiovascular risk among the markers tested.
The initial studies linking fat to heart disease were conducted primarily in North America and Europe, which has the highest consumption of fat worldwide. In western cultures, where there is an excess of fat, reducing fat may play a role in lowering heart disease, as long as people aren’t replacing the fat with carbohydrates. In other parts of the world, where carbohydrates make up a large part of the diet, cutting back on carbs may make more sense than focusing on fat. Further research is required to determine optimal levels of fat and carbohydrates. The investigators suggest that dietary guidelines should be reconsidered in light of these findings.
Researchers at the 2017 European Society of Cardiology (ESC) Congress have also called for a reconsideration of global dietary guidelines on dietary fat intake. This discussion is based on increasing data that do not support the current recommendation to limit total fat intake to less than 30 percent of energy and saturated fat intake to less than 10 percent of energy. At the ESC congress, it was noted that limiting total fat consumption is unlikely to improve health in populations, and a total fat intake of about 35 percent of energy with concomitant lowering of carbohydrate intake may lower risk of total mortality.
In summary, the PURE investigators note that “For decades, dietary guidelines have focused on reducing total fat and saturated fatty acid (SFA) intake based on the presumption that replacing SFA with carbohydrate and unsaturated fats will lower LDL-C and should therefore reduce CVD events. PURE provides a unique opportunity to study the impact of diet on total mortality and CVD in diverse settings, some settings where over-nutrition is common and others where under-nutrition is of greater concern”.
Reference:
Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort studyDehghan, M, Mente, A, Zhang, X et al. Lancet; 29 August 2017. DOI: http://dx.doi.org/10.1016/S0140-6736(17)32252-3