WHO dietary fat guidance fails to consider crucial evidence
Author: Louise Prime
World Health Organisation (WHO) draft guidelines on dietary saturated and trans fatty acids for adults and children have excluded some important evidence – and general advice to reduce total saturated fatty acids will work against the intentions of the guidelines and weaken their effect on chronic disease incidence and mortality, experts have warned in The BMJ today. In their analysis*, they call for a food-based translation of the recommendations for saturated fat intake that would “avoid unnecessary reduction or exclusion of foods that are key sources of important nutrients”.
The authors pointed out that we do have consensus that eliminating industrially produced trans fatty acids will reduce the incidence of cardiovascular disease (CVD) and mortality. For example, Denmark in 2004 banned foods containing more than 2% total fat as trans fat (and analyses have attributed the subsequent larger decline in coronary heart disease mortality in Denmark compared with other EU countries to the elimination of trans fat from foods); similar legislation is soon to be implemented throughout the European Union, and the US Food and Drug Administration no longer considers industrial trans fats to be “generally regarded as safe”.
However, they warned, because many governments base their national dietary recommendations on what they assume to be “state of the art” evidence in WHO dietary guidelines, they can affect the health of billions of people – so it is crucial that they are based on consistent science and valid conclusions.
The new draft guidance from WHO, published for consultation in May 2018, recommends reducing intake of total saturated fatty acids (SFA) to less than 10% of total energy consumption and replacing this with polyunsaturated fat and monounsaturated fat to reduce the incidence of CVD and related mortality. But, argued the authors of the analysis, this fails to take into account considerable evidence that the health effects vary for different SFA and that the composition of the food in which they are found is crucially important. They explained that SFA are found in a wide diversity of foods that vary in both composition and structure – stearic acid in dark chocolate, palmitic acid in meat, and heptadecanoic acid in dairy products each have completely different physiological effects – and furthermore, the food matrix in which the SFA exist has major importance for these effects.
They cite several recently published meta-analyses of observational studies and randomised controlled trials (RCTs) that found that total SFA intake is not associated with non-communicable diseases including coronary heart disease, CVD, and all-cause mortality. On the other hand, a Cochrane analysis of data from only 15 RCTs found an association between reduced intake of SFA and a 17% decrease in the composite endpoint of cardiovascular events – but no statistically significant association between reducing SFA and total mortality, CVD mortality, fatal and non-fatal myocardial infarction, non-fatal myocardial infarction, stroke, coronary heart disease events, and coronary heart disease mortality.
They said: “The WHO draft guidelines exclude substantial evidence derived from observational studies and meta-analyses of prospective cohort studies. The guideline argues that the quality of evidence for relevant outcomes from such studies is lower than from analyses of RCTs and that it was not possible to assess the potential differential effects of replacing saturated fatty acids with different nutrients. But observational studies are valuable for assessing the association between saturated fat and long-term endpoints, such as cardiovascular disease.”
They pointed out that lessons should be learned from previous scientific and policy “missteps” that have resulted in unnecessary deaths, and warned that recommendations to reduce SFA could lead to reduced intake of nutrient-dense foods that are important for preventing disease and improving health – and could mislead governments, consumers, and industry towards promoting foods low in SFA but rich in refined starch and sugar.
They concluded: “The WHO guidelines on saturated fat should consider different types of fatty acids and, more importantly, the diversity of foods containing saturated fatty acids that might be harmful, neutral, or even beneficial in relation to major health outcomes. We strongly recommend a more food-based translation of how to achieve a healthy diet and reconsideration of the draft guidelines on reduction in total saturated fatty acids.”
*Astrup A, Bertram HCS, Bonjour J-P, et al. Analysis: WHO draft guidelines on dietary saturated and trans fatty acids: time for a new approach? BMJ 2019; 365: l4137 doi: 10.1136/bmj.l4137.