The PURE trial wanted to look at the role of carbohydrates, protein
The study found that highest versus lowest total fat intake was associated with a 33% reduction in total mortality and a 30% reduction in non-cardiovascular related mortality. When examining highest versus lowest saturated fat intake, the authors found a 14% reduction in total mortality and a 21% reduction in risk of stroke.
On the flip side, the authors found that highest versus lowest carbohydrate intake was associated with a 28% increased risk of total mortality and 36% increased risk of non-cardiovascular mortality.
So, does this mean that we can all go back to eating saturated fat and that carbohydrates are the enemy? Well, not necessarily. There were a few key limitations in the study that make the results questionable.
The highest intake of total fat in the study was 30.5% and saturated fat intake was 10.9%. These levels are close to what the USDA recommends: total fat intake less than 30% and saturated fat intake less than 10%. However, both United States and Europe consume fat intakes far greater than these numbers. Thus, this adds evidence to the current guidelines but does not show that saturated fat is healthy.
When evaluating carbohydrates, it was interesting was that all types were lumped together. There was no differentiation among simple versus complex carbohydrates. Previous studies have shown that refined grains are associated with higher heart disease risk and whole grains are cardioprotective. In this study, the highest consumption of carbohydrates was in lower income-countries where carbohydrates available were in mostly the refined form.
Another interesting aspect of the study was the funding disclosures. This consisted of AstraZeneca [Canada], Sanofi-Aventis [France and Canada], Boehringer Ingelheim [Germany and Canada], Servier, GlaxoSmithKline, Novartis and King Pharma.
Other general limitations of the study were the use of food frequency questionnaires that can have recall bias; a single dietary assessment at the baseline; cohort study that only shows correlation and not causation.
The bottom line here is that the study doesn’t merit changing our recommendation for limiting saturated fat to less than 10% or total fat intake to less than 30%. However, it does show that eating higher amounts of low-quality carbohydrates is detrimental to our health. Once again, a healthy eating pattern composed of whole foods, mostly plants is ideal for optimal health.
Dehghan, M., et al. (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(10107): 2050-2062.