Facts and Fictions: “The PURE Diet”

News has reached the lay public about what is termed the PURE diet. Over the last year, confusion and controversy have emerged. What was the study about and what makes understanding the findings of the study so challenging?

The Study

The Prospective Urban Rural Epidemiology (PURE) investigators conducted a large, prospective, cohort study, on 135,335 adults (35-70 years) from 18 countries in five continents enrolled from 2003-2013, with follow-up at about 7.4 years.1 Validated food frequency questionnaires were used to record dietary intake. Food intake (protein, fat, and carbohydrate) was categorized using quintiles and percentage of energy from nutrients was analyzed. Primary outcomes were total mortality and cardiovascular events such as heart failure, stroke, fatal cardiovascular disease, and non-fatal myocardial infarction.1 Using hazards ratios and multivariate Cox modeling, the research found that a high carbohydrate intake (providing > 60% of energy) was correlated with the following results: adverse impact on total mortality and on non-cardiovascular disease mortality. Additionally, they found that higher fat intake was correlated with a lower risk of total and non-cardiovascular disease mortality as well as stroke. 1 The researchers summarized that the findings of the PURE study do not support current clinical dietary recommendations to reduce total fat intake to less than 30% or current guidelines on saturated fats.

The Challenges

Many headlines portrayed the PURE study as the PURE DIET, yet the researchers more generally studied food intake in 18 countries. This attention to naming the study as a diet may have occurred because Americans are used to hearing about the latest new “diet.” However, this approach confuses the lay public. A particularly emphatic internet headline reads, “A low-fat diet might kill us, finds the new PURE study.”2 Preventive cardiology nurses must continue to help patients understand information about nutrition and prevention. Importantly, much discussion must occur between researchers and clinicians to determine how applicable the findings are to prevention in the US.

Many specific unanswered questions remain about the findings according to an article in Lancet:3

Further analysis by the PURE study investigators is needed to evaluate whether meats and dairy reduce mortality. To do this, a relationship of specific animal products3 to mortality must be determined.

The fact that some counties studied might have both micronutrient-poor carbohydrates and micronutrient-rich meats3 may be a confounder in carbohydrate versus fat comparisons in these country’s results. The PURE study group will need to sort out this possible intervening micronutrient variable.

The role of high carbohydrate in mortality is not clear.3 Clarification is needed about the associations between whole and refined grains, added sugars, and mortality.

The PURE study is not a randomized trial, and it has questioned long-held tenants on what constitutes a healthy diet for cardiovascular prevention.3 Further research, in the form of well-controlled randomized trials, is needed to replicate the findings before prevention cardiovascular nurses do actual large-scale clinical applications of its findings in practice.  

  1. Dehghan, M., Mente, A., Zhang, X., Swaminathan, S., Li, W., Mohan, V., Yusuf, S. (2017) Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. Lancet, 390, 2050-2062. doi: 10.1016/S0140-6736(17)32252-3
  2. Eenfeldt, A. A low-fat diet might kill you, finds the new PURE study. (August 31, 2107). https://www.dietdoctor.com/low-fat-diet-might-kill-finds-new-pure-study
  3. Ramsden, C. E., Domenichiello, A. F. (2017) PURE study challenges the definition of a healthy diet: but key question remain. Lancet, 390, 2018-2019. https://www.thelancet.com/journals/ lancet/article/PIIS0140-67361732241-9/fulltext

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