The 2018 WHO draft guidelines on dietary saturated fatty acids and trans fatty acids recommended reducing total saturated fatty acids to less than 10% of total energy consumption and replacing it with polyunsaturated and monounsaturated fatty acids.
However, the recommendations failed to take into account “considerable evidence that the health effects vary for different saturated fatty acids and that the composition of the food in which they are found is crucially important”, claimed Arne Astrup, a nutrition professor at the University of Copenhagen, and colleagues in a study published in The BMJ.
Food composition has a substantial effect on lipid digestion, absorption kinetics and postprandial lipaemia, “which is an independent risk factor for cardiovascular disease”, the study argued.
Professor Nita Forouhi of the MRC Epidemiology Unit at the University of Cambridge, said the authors’ argument that WHO guidelines on dietary fat should consider the different types of saturated fatty acids and the diverse foods that contain them, was consistent with her team’s findings.
“Our own EU-funded research in people in eight European countries showed the varying effects of different types of blood saturated fatty acids on the risk of type 2 diabetes,” Forouhi said.
‘Recent progress in nutrition science’
“A call to distinguish between different food sources of saturated fats, not focus on the nutrient alone, is in line with the recent progress in nutrition science, but we must be mindful to not pre-judge the final report that is yet to be released by the WHO following the public consultation period that ended in June 2018.”
Professor Judy Buttriss, director general of the British Nutrition Foundation, said the authors rightly pointed out that different saturated fatty acids had different health effects, as not all saturated fatty acids raised blood cholesterol level.
However, when it came to giving practical advice, she believed it was very difficult to give simple guidance on the specific fatty acids we consumed.
“A dietary pattern approach to reducing disease risk and promoting health is becoming more popular,” Buttriss said. “However, we do need more research on the specific effects of changing dietary patterns on health as this is a very complex area to investigate in studies, not least because we need a multitude of different essential nutrients regularly from the food we consume.
“The opinion piece in the BMJ suggests that advice to reduce saturated fat might lead people to exclude foods that are rich in nutrients. But this is not encouraged in the UK’s Eatwell Guide, which … recommends choosing lower-fat versions of dairy foods most of the time; it does not suggest that dairy foods be excluded.”
Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, believed the opinion piece raised some valid questions regarding dietary guidelines concerning saturated fatty acids, “but it in no way suggests we got it wrong on saturated fats”.
‘High in saturated fatty acids’
“It does raise the important issue about labelling all foods that are high in saturated fatty acids (including dairy, oily fish and nuts) as unhealthy, because evidence has emerged from prospective cohort studies suggesting that liquid milk and yoghurt (but not butter), oily fish and nuts are associated with a lower risk of cardiovascular disease (CVD),” Sanders said.
“However, red meat and meat products, which are major sources of saturated fatty acids, are consistently linked to a greater risk of CVD. So this is not the green light for saturated fats.”
Naveed Sattar, professor of metabolic medicine at the University of Glasgow, said while the opinion piece was written by nutritional experts, and some historical points were well made, the overall message was “somewhat confusing and contains some areas of inaccuracy”.
“If people interpret this as meaning ‘no need to reduce saturated fat’, I would worry that could have adverse consequences for public health,” he claimed.
“For example, despite what the authors state, that saturated fat intake in excess increases bad LDL-cholesterol levels is not in doubt, and neither is the link between high LDL-c and cardiovascular disease.
“Also, the best trials do show lower heart disease with less saturated fats and all other bad heart-related outcomes appear to be reduced, even if the power in some of the analyses were limited.
“The authors also state evidence from a mix of selected nutritional trials and observational studies, so it is not easy to assess the objectivity of their points.”