March 5, 2014

expert reaction to editorial on saturated fats

In an editorial for the journal Open Heart Dr James DiNicolantonio argued that diets low in saturated fat don’t curb heart disease risk or help you live longer.

Prof Bruce Griffin, Professor of Nutritional Metabolism at the University of Surrey, said:

“The review by DiNicolantonio provides yet more fuel for the debate over the relative effects of saturated fat and refined sugars on cardiovascular health, which exists, primarily, because there is no definitive evidence to support a causal relationship between diet and disease.

“Nutritional science is complex and imperfect, making it feasible to construct logical and compelling arguments that either one of these dietary components can exert more or less cardiovascular risk.  To suggest that the theory relating saturated fat to increased total cholesterol is flawed, is nonsense, and contradicts 50 years of evidence-based medicine.  It also invalidates our clear understanding of the molecular and metabolic mechanisms by which saturated fat raises serum LDL. 

“What is ‘flawed’ is the author’s interpretation of how LDL subtypes confer risk and respond to saturated fat.  This cannot explain the contentious view that the effect of saturated fat on LDL is innocuous.  A more balanced review of the overall evidence would reveal that the risks from saturated fat and refined sugars are not mutually exclusive, but co-exist together in our diet. 

“Moreover, it is essential to appreciate that one size does not fit all in terms of the origins of cardiovascular disease, which will differ(genetic, dietary) in different people.  Likewise, dietary factors will have different effects in these different people.  We know that sugars may contribute more to the development of cardio-metabolic risk in obesity and diabetes, whilst saturated fat is more effective in lowering cholesterol in people with raised serum LDL.

“In other words, the debate about which is worse, and whether dietary guidelines are wrong is less important than the relative impacts of saturated fat and sugar on the variable expression of cardiovascular disease in at risk populations.”

Prof Tom Sanders, Head of Diabetes and Nutritional Sciences Division in the School of Medicine at King’s College London, said:

“Dietary guidelines for prevention of cardiovascular are based on the premise that reductions in the mean population serum LDL cholesterol and blood pressure will reduce population risk of CVD (cardiovascular disease).

“This article rubbishes the relationship with saturated fat and CVD, misrepresents the scientific evidence and then goes on to put the blame on sugar.  It is beyond reasonable doubt that elevated LDL (low density lipoprotein) cholesterol is a major determinant of risk factor for cardiovascular disease.  The saturated fatty acids palmitic, myristic and lauric acids raise LDL cholesterol in increasing order in meta-analysis human experimental studies¹.  Sugar intake does not affect LDL-cholesterol or blood pressure.

“Diabetes increases risk of CVD but diabetes is not caused by eating sugar.  The relative risks of sugar intake with risk of obesity are very modest compared with obesity and physical inactivity.  While sugar sweetened beverages contribute to obesity, where intakes are high it’s probably because it is providing extra calories.  However, the high consumers of sugar fizzy drinks are young people – not older people who those most at risk of CVD.  It is likely that high intake of sugar-sweetened beverages are contributing to obesity rather having direct effects on CVD risk.  Refocusing dietary advice on sugar and away from fat modification and reduction is not helpful.  

“Large reductions in saturated fatty acid intakes have occurred in the UK and other Western countries over the past 25 years so intakes are now close to guideline amounts (less than 11% energy).  This has been achieved by changes in dietary habits (reducing the use of butter/spreads high in saturated fats) and changes in the food supply with unhydrogenated vegetable oils replacing animal fats.  The changes have been in parallel with falls in average serum cholesterol levels in the UK, Western Europe, Australasia and the USA² as well as in CVD incidence.

“In the UK total fat intake has fallen in absolute terms and as a proportion of energy, while sugar intake has remained as a proportion of the energy relatively unchanged (around 21% energy) according to the nationwide surveys (with non-milk extrinsic sugars providing 11-12% energy).  The UK has experienced a 55% fall in cardiovascular disease since 1997³.  Some of this is due to lower blood cholesterol and blood pressure and decreased smoking prevalence despite the increase in obesity and diabetes.

“People eat foods, not nutrients.  Dietary advice to avoid fatty meat products, choose reduced fat dairy produce, and to restrict intakes of cakes, biscuits and puddings, which are often both high in saturated fat and sugar, and to select foods containing unsaturated oils such as nuts, fish and vegetable oils remain good sense.  Those who fail to learn the lessons of history are likely to repeat its errors.”

Tom Sanders is also a member of the Scientific Advisory Committee of the Global Dairy Platform.

¹Sanders TA (2013) Reappraisal of SFA and cardiovascular risk. Proc Nutr Soc, 1-9.

²Sanders TA (2014) Protective effects of dietary PUFA against chronic disease: evidence from epidemiological studies and intervention trials. Proc Nutr Soc 73, 73-79.

³ Bajekal M, Scholes S, Love H, Hawkins N et al. (2012) Analysing recent socioeconomic trends in coronary heart disease mortality in England, 2000-2007: a population modelling study. PLoS Med 9, e1001237.

Prof Brian Ratcliffe, Professor of Nutrition at Robert Gordon University, Aberdeen, said:

“This editorial is a welcome addition to the debate about what is known as the ‘lipid hypothesis’ of the dietary links to cardiovascular diseases. For the last three decades, accumulating evidence has not provided strong support for the dietary recommendations regarding reducing fat and saturated fat intake.  DiNicolantonio does not even touch on the evidence which shows that low fat diets (admittedly lower than the current recommendations) have been associated with poor mood and even depression.  Many who adhere to dietary dogma have chosen to ignore the uncomfortable facts that did not fit the hypothesis. 

“The dietary links with cardiovascular diseases are not easy to tease apart and much of the earlier work that supported the ‘lipid hypothesis’ used relatively crude methods.  For example, detailed fractionation of lipoprotein particles was not available for early studies and there was little awareness of the variety of human genotypes with differential responses to dietary changes.  Keys was one of the architects of this dietary fat hypothesis but even he recognised that not all saturated fatty acids are the same (embodied in what became known as the Keys’ equations for predicting the effects of fatty acids on blood cholesterol). 

“In what is otherwise a useful summary of some of the issues, it seems that DiNicolantonio falls into his own trap by making a simplistic association of the increases in intake of refined carbohydrates and modified corn syrup that have been seen in the USA with the rise in the prevalence of overweight and obesity.  The latter has occurred across much of the developed world without such obvious associations with dietary carbohydrate.  The most recent Cochrane review concluded that addressing the quality of fat in the diet could reduce cardiovascular events by 14% and perhaps that is worthy of consideration.”

‘The cardiometabolic consequences of replacing saturated fats with carbohydrates or Ω-6 polyunsaturated fats: Do the dietary guidelines have it wrong?’ by James DiNicolantonio published in Open Heart on Wednesday 5 March.