PURE study findings: Should dietary guidelines on fat be challenged?

Posted on: September 11, 2017

Recent findings from the Prospective Urban-Rural Epidemiology (PURE) study involving 135.000 people from 18 countries found that high intake of fat was negatively associated with total mortality and non-cardiovascular disease, while high carbohydrate intake was positively associated. The study was published in the  last week. Based on these finding, the authors called for a reconsideration of global dietary guidelines. However, data of this very large observational study, should be put into perspective and treated with caution.

About the PURE study
The PURE study documented diet in 135.335 individuals, aged 35-70 years, from 18 different counties across the world.Consumption of carbohydrates, total fat and types of fat were calculated from validated food frequency questionnaires and country-specific nutrient databases. Additional questionnaires were administered simultaneously, to collect a large variety of co-variables (e.g. age, education, physical activity, etc), which were included in the multivariable association models. The primary outcomes were total mortality and major cardiovascular events. Secondary outcomes were all myocardial infarctions, stroke, cardiovascular disease mortality, and non-cardiovascular disease mortality.

The main findings
During a follow-up period of 7.4 years, 5796 people died and 4784 had a major cardiovascular event; 2143 people experienced a myocardical infarct, and 2234 were hit by a stroke. Total mortality and non-cardiovascular disease mortality were positively associated with total carbohydrate consumption (46.4 - 77.2 en%;) and  related negatively to the intake of total fat (10.6 - 35.3 en%).

Associations of these clinical outcomes with saturated (2.8 - 13.3 en%), monounsaturated (3.4 - 12.5 en%) and polyunsaturated (2.1 - 8.5 en%) fatty acid intakes were also significant and negative. In general, macronutrient intakes were not associated with cardiovascular risk. The risk of stroke, however, appeared lower the higher the saturated fat consumption.

Reaction and response
Responding to the findings, Dr Gerard Hornstra, Professor emeritus at Maastricht University, pointed out that in the overall impressive study, replacing macronutrient were not taken into account. “This is a major weakness, since differences in calories consumed from one macronutrient are usually balanced by the compensatory intake of energy from one or more of the other macronutrients”

Although, the large number of volunteers included is a strength of the study, the variations in lifestyle, socioeconomic status, access to proper medical care, etc. might be too large for adequate adjustments. “I would have welcomed separate risk analyses for the seven regions the 18 countries had been categorized into. This would facilitate the comparison of the results  with similar studies in the literature, which have mainly been performed in North America and Europe”, said Hornstra.

Another strength of the present study is the broad range of carbohydrate intakes, which possibly explains the stronger association between carbohydrate intake and total mortality in earlier studies. It should be mentioned, though, that in the present  study the risks of total mortality and of major cardiovascular disease only start to increase at dietary carbohydrate levels of 60 and 65 en%, respectively. “Such intake levels are uncommonly high for European countries and therefore, these observations lend hardly any support for advocating the use of low carbohydrate/high fat diet in Europe”, he said.

The use of food frequency questionnaires to assess food and nutrient intake is usually considered a major limitation in observational studies, as it potentially leads to misclassification and may attenuate potential associations. “However, it’s the only practical way to measure food and nutrient intakes in large populations and, therefore, the results should be treated with caution”, according to Hornstra.

For more information on the study please contact us at info [at] palmoilalliance [dot] eu