PURE study makes headlines, but the conclusions are misleading

Portside Date:
Author: The Nutrition Source
Date of source:
Harvard T. H. Chan School of Public Health

Last week, The Lancet published results from the Prospective Urban Rural Epidemiology (“PURE”) study that made headlines: “Study Challenges Conventional Wisdom on Fats, Fruits, and Vegetables;” “PURE Shakes Up Nutritional Field;” “Huge New Study Casts Doubt on Conventional Wisdom About Fat and Carbs.”

 Following over 135,000 participants spanning five continents, the study is indeed a large one. However, its findings are not as novel or disruptive as these sensational headlines suggest. Let’s take a closer look.

 Study data and findings

 PURE researchers collected self-reported dietary data from 135,335 people in 18 countries, and grouped them according to the amount of carbohydrate, fat, and protein they consumed. After tracking participants’ health over a seven year period, researchers found that those with the highest intake of dietary fat (35% of daily calories) were 23% less likely to have died than those with the lowest intake of fat (10% of daily calories). Oppositely, for carbohydrates, those with the highest intake (77% of daily calories) were 28% more likely to have died than those with the lowest intake (46% of daily calories). [1] From these findings the authors’ main conclusion is 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.”

Key methodological problems

The takeaway

Large-scale efforts to study the health effects of diet in developing countries are important, but this study is fraught with methodological problems—especially confounding by different degrees of socio-economical development in different countries and questionable dietary intake data. Dr. Frank Hu, Chair of the Department of Nutrition at the Harvard Chan School of Public Health, notes that one should look beyond the sensational headlines and the abstract of the paper:

The main messages for nutritional advice have not changed: follow a healthy dietary pattern that includes abundant amounts of vegetables, fruits, whole grains, legumes, and nuts; moderate amounts of reduced-fat dairy products and seafood; and lower amounts of processed and red meat, sugar-sweetened foods and beverages, and refined grains. Such a dietary pattern does not need to limit total fat intake but the main types of fat should be unsaturated fats from plant sources rather than animal fat.


  1. Dehghan M, Mente A, Zhang X, et al, on behalf of the Prospective Urban Rural Epidemiology (PURE) study investigators. Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. Lancet 2017; published online Aug 29.
  2. Zong G, Gao A, Hu FB, Sun Q. Whole grain intake and mortality from all causes, cardiovascular disease, and cancer: a meta-analysis of prospective cohort studies. Circulation 2016; 133(24): 2370-80.
  3. Butt MS, Sultan MT. Levels of trans fats in diets consumed in developing economies. J AOAC Int. 2009;92:1277-1283
  4. Hooper L, Martin N, Abdelhamid A, Davey Smith G. Reduction in saturated fat intake for cardiovascular disease. The Cochrane database of systematic reviews. 2015:CD011737

Shen X, Fang A, He J, Liu Z, Guo M, Gao R, Li K. Trends in dietary fat and fatty acid intakes and related food sources among chinese adults: A longitudinal study from the china health and nutrition survey (1997-2011). Public Health Nutr. 2017:1-10

Source URL: https://portside.org/2018-03-05/pure-study-makes-headlines-conclusions-are-misleading