The PURE study; low fat diets increase risk of death

This was the nutrition news in August 2017. More evidence of the mainstream media trying to confuse the public and reinforce the nations poor food choices. The public love to read stories that support their bad habits. Thankfully, many plant-based physicians have given a more scientific critique of the data. So, what is the background to this story? There have been 3 back to back papers published in the Lancet Journals reporting the results of the PURE study (Prospective Urban Rural Epidemiology), which followed 135, 335 individuals from 18 low, middle and high-income countries. A country-specific food frequency questionnaire (FFQ) was completed at baseline and the group was followed for a median of 7.4 years. 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. Nutrient intake was classified into carbohydrates, fats and protein. Fats were subdivided into saturated, monounsaturated and polyunsaturated. The main conclusions that have been reported by the media are that the higher the intake of carbohydrates, the higher the risk of disease and death and that vegetables/fruits/legumes can improve health and mortality but eating 3 portions a day is sufficient and the beneficial effects plateau at this level of intake with increasing number of portions not having an additional benefit.

There are some positive aspects to this study. It is large and includes people from low and middle income countries that are not usually represented in nutrition studies. In addition, it does confirm to some extend that the type of fat in the diet matters; mono and polyunsaturated fats are better than saturated fats. However, I think the there are many aspects of the study that should make us wary of the conclusions. A whole essay could be written in this regard but I summarise some salient points that I think are important.

The study only asked participants at baseline about food intake and therefore assumes that dietary intake did not change over this 5-10 year period. The FFQ relies on peoples memory of what they ate over a preceding time period and this has inherent inaccuracies. Carbohydrates were not broken down into different types i.e. refined versus whole foods. The study was conducted from 2003 so it can be assumed that much of the carbohydrates eaten are refined, especially in high-income countries. This is likely to account for the detrimental effect of carbohydrates on health outcomes. Those eating the highest carbohydrate and lowest fat diet were from low and middle income countries and therefore the inferior health outcomes could also be explained by poverty, less food security (as evidenced by lower protein intake) and less access to healthcare. Those eating the highest fat diets i.e. high-income countries, had a lower risk of non-cardiovascular mortality; Is this not just a reflection of access to healthcare? This is not even mentioned in the paper. There is a paradox between the papers. One paper concludes that vegetables, fruits and legumes improve health outcomes but the other concludes that high carbohydrate diets are detrimental to health. What are vegetables, fruits and legumes if not carbohydrates! The papers did not find any associations of these major macronutrients on cardiovascular disease and mortality.

The conclusions therefore were that the status quo is fine; carry on eating saturated fats. However, when cardiovascular disease is the main cause of death in high-income countries, shouldn’t we be recommending a diet a that can prevent, arrest and potentially reverse cardiovascular death?

The observational data presented in these papers has to be read in the context of previous data from more robust interventional and randomised studies that proceed it. It can not replace the information that we know already. The discussion sections of the paper fails to mention these studies. We already know from interventional and randomised studies that a shift to a more low fat (i.e. less than 10% of calories), whole food plant based diet or traditional Mediterranean diet consisting predominantly of whole grains, legumes, vegetables and fruits can reduced the risk of cardiovascular disease, diabetes and hypertension. It can control and reverse type 2 diabetes better than medication and it can prevent, arrest and reverse heart disease. These facts have been proven with more robust trial methodologies than the PURE study. In addition, observational data from earlier decades when traditional diets in places like India, Africa, China and Japan were composed of predominantly whole plant foods and did not include processed or refined carbohydrates demonstrated that these communities had very a low incidence of lifestyle-related diseases such as heart disease, diabetes and cancer. These communities that are still consuming traditional, mainly plant-based diets (‘blue zones’ ) and living longer than any other communities around the world.

Once again, the media have provided sensationalised headlines to promote a diet that will please agribusiness, large food corporations and big-pharma. If we continue to eat a diet high in saturated fat we will continue to be fat and sick and the only people to benefit will be pharma and food corporations that are profiting from our ill health.