© Matthew’s Friends 2017
PURE STUDY REVIEW
Elizabeth Neal MSc PhD RD
Research Dietitian, Matthew’s Friends Clinics
Honorary Research Associate, UCL - Institute of Child Health
This paper, recently published in the Lancet, reports results from a large 10-year epidemiological study of individuals aged 35-70 years: the Prospective Urban Rural Epidemiology (PURE) study. Dietary intake of 135,335 participants from 18 countries (five continents) was recorded using country-specific validated food frequency questionnaires; this included seven worldwide regions representing low, middle and high incomes and prevalence of both over- and under-nutrition. The aims of the study were to assess the association of fat (total, saturated and unsaturated) and carbohydrate intakes with total mortality, major cardiovascular disease (CVD) events, CVD mortality, non-CVD mortality, myocardial infarction and stroke.
For intakes of each macronutrient (carbohydrate, fat and protein), participants were divided into five groups (quintiles) based on the percentage of total energy in their diets provided by that nutrient; this was also done for saturated, monounsaturated and polyunsaturated fatty acid intakes. Median participant follow-up was 7.4 years during which 5,796 died and 4,784 had a major CVD event. Incidence of mortality (total, CVD and non-CVD), major CVD events, myocardial infarction and stroke was compared between nutrient intake quintiles with adjustments for age, sex, socioeconomic status and poverty.
Results showed that a higher carbohydrate intake was associated with an increased risk of total mortality and non-CVD mortality (but not CVD or CVD mortality); this increasing trend in mortality risk only occurred among those who consumed more than 60% of energy from carbohydrate. Total fat and intake of each type of fat was associated with a lower risk of total mortality and non-CVD mortality with higher total and saturated fat intakes also being associated with a lower risk of stroke. Protein intake was also inversely associated with risks of total mortality and non-CVD mortality. These results were unchanged when compared between Asian and non-Asian countries. Using multivariable nutrient density models, an additional estimate was made of the effect of replacing 5% of the energy from carbohydrate with the equivalent provision from other macronutrients. Replacement of carbohydrate with polyunsaturated fatty acids was associated with an 11% lower mortality risk and a 16% lower risk of non-CVD mortality; replacement with saturated fatty acids was associated with a 20% lower risk of stroke.
These results have significant implications for global dietary guidelines which have been largely based on data from North America and Europe (where excess nutrition is a concern) and currently recommend total fat should be limited to less than 30% of energy, with saturated fatty acids less than 10% and replaced with unsaturated sources. This study raises questions about these guidelines especially in regions of the world where under-nutrition may be more prevalent and carbohydrate intakes may be higher. The authors suggest that limiting carbohydrate intake (when it is high) might improve health although the absence of association between low carbohydrate intake and health outcomes does not provide support for very low carbohydrate diets; they recommend moderate intakes of 50-55% energy may be the most appropriate to meet the short term energy demands of physical activity. Results also indicate that limiting total fat consumption is unlikely to improve population health, indeed a very low saturated fat intake may be harmful, and so current restrictions on fat intake should be removed.