July 5, 2016

expert reaction to dietary fats and risk of death

Publishing in JAMA Internal Medicine, an observational study looked at different types of dietary fat intake and mortality. They reported that different kinds of dietary fat had different associations with total and cause-specific mortality.

Dr Nita Forouhi, from the MRC Epidemiology Unit at the University of Cambridge, said:

“In the currently controversial dietary fat research landscape, this large study provides robust observational evidence for the health benefits of swapping saturated fat with polyunsaturated fat.

“While other continued efforts are important to consider the totality of the research evidence from different study designs that include observational as well as randomised clinical trial evidence, this study is helpful in making a strong case to promote dietary guidance that focuses on the quality or types of dietary fat rather than on total fat intake. Further work should also seek to tease out the differences and the reasons for the differences in the association of saturated fat consumption with different outcomes such as coronary heart disease, stroke, total cardiovascular disease, and mortality, as currently different researchers focus on diverse outcomes.

“Some key additional results from this study are important and should not be buried in the limelight of the saturated fat issue. This study provides robust evidence to cast aside the doubts previously raised about linoleic acid, the omega-6 polyunsaturated fatty acid found typically in vegetable oils. Opening new horizons, this study should stimulate further understanding of the role of different types of fats beyond cardiovascular disease such as their finding of an inverse association of types of omega-3 polyunsaturated fatty acids and neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease, as well as lower respiratory disease related deaths.

“It is now timely and appropriate to put effort into giving clear guidance on the health benefits and harms of the food sources of fat, moving beyond the issue of types of fat, the macronutrient. Translating the message to reduce saturated fat intake through substituting with increasing unsaturated fat intake will need a strong focus on the recognition that it is foods that people consume. We and others have been building an evidence base that foods such as red and processed meat versus dairy, though both rich in saturated fat, have discordant health effects.”

Dr Ian Johnson, emeritus fellow at the Institute of Food Research, said: 

“This large and rigorous observational study from a very experienced and reliable research group examined the effects of dietary fat intake on risk of death in two large groups of men and women in the USA.  Diets were repeatedly assessed for up to three decades, using well validated food-frequency questionnaires, and the results were adjusted to account for the effects of other aspects of lifestyle and health.

“The findings indicate that diets containing relatively high levels of saturated fat were associated with higher mortality compared to diets richer in unsaturated fats.  Remarkably, replacing only 5% of total calorie intake from saturated fat (around 15g) with the same quantity of polyunsaturated fat was associated with a 27% lower risk of death from heart disease, cancer and other causes.

“These findings are consistent with current public health recommendations in the UK and elsewhere, and particularly with the concept of a beneficial Mediterranean-style diet, rich in unsaturated fats from plants, fish and olive oil.

“Recently a number of books and opinion pieces have popularised the idea that conventional dietary advice, recommending consumption of vegetable oils and other products rich in unsaturated fats in preference to saturated fats from animal products, has been shown to be wrong.  This study should do much to redress the balance. There is nothing in these results consistent with the notion that ‘butter is back’.”
Dr Gunter Kuhnle, Associate Professor in Nutrition and Health, University of Reading, said:

“There has been a lot of public discussion about dietary guidelines recently, especially a call to end the demonisation of fat (and demonise carbohydrates instead). These discussions were often accompanied by claims that there was no evidence whatsoever for the current dietary guidelines – a claim based on a very selective interpretation of the data available.

“This approach is dangerous as it not only confuses the public, but also discourages the public from following sound recommendations.

“Diet is an important modifiable risk factor, and even though the effect on the individual can be very small, the impact can be large for the entire nation.

“A sound evidence base for dietary recommendations is therefore crucial, and this can only be achieved by regularly reviewing results from large studies – as done for example by Public Health England.

“This latest study contributes to this evidence and will inform future decisions. It is based on the observation of more than 120,000 volunteers over around 30 years and investigated how different types of dietary fat affect health. The results of the study broadly confirm current dietary recommendation and in particular show that total saturated fat intake is associated with a higher, unsaturated fat with a lower risk for all-cause mortality.

“However, there is an important limitation: there are many different types of fat – as there are many different types of carbohydrates, something often forgotten by the most vocal critics of current dietary guidelines.

“While the current study does distinguish between different types of saturated and unsaturated fats, this is still not detailed enough: previous studies have for example shown that saturated fats from dairy products – but not others – are associated with a reduction of disease risk.

“Moreover, the current study relies on self-reported data for diet, which is likely to introduce bias and does not provide the same level of detail than more objective methods. Fortunately, recent developments have allowed a better assessment of dietary intake, and this will help us to improve dietary recommendations.”

* ‘Association of Specific Dietary Fats With Total and Cause-Specific Mortality’ by Dong D. Wang et al. will be published in JAMA Internal Medicine at on Tuesday 5th July.

Declared interests

Dr Kuhnle: Employment: Associate Professor at the University of Reading.  Grant funding: Investigation of links between polyphenol intake and health – EU, Mars, Horizon.  Appointments: EFSA Working group – risk assessment of soy isoflavones.  Memberships: British Mass Spectrometry Society, British Nutrition Society, Registered Nutritionist (Reg. Nr. 8236); 2011 to 2012 member of ‘Biomarker group’ at ILSI Europe.  Other financial interests: Vineyard owned by family.

Dr Johnson: none declared.

Dr Forouhi: none declared.