July 18, 2016

expert reaction to review paper looking at Mediterranean diet, fat intake and health outcomes

A paper published in the journal Annals of Internal Medicine has compared different kinds of diet and reports that a Mediterranean diet with no restrictions on fat intake may reduce incidence of diseases including breast cancer but doesn’t affect all-cause mortality.

Dr Gunter Kuhnle, Associate Professor in Nutrition and Health, University of Reading, said:

“There has been a lot of public discussion about the role of fat in dietary recommendations recently. Even though there is a broad consensus about dietary recommendations, this discussion has given the false impression of serious controversy.

“This latest study is a review of the evidence currently available and investigates whether the Mediterranean diets are healthier than Western diets. Despite the popular perception of the benefits of the Mediterranean diets, there is very limited evidence supporting this and most is based on observational studies.

“The two clinical trials included in the review did show a Mediterranean diet had some benefit for cardiovascular diseases, diabetes and breast cancer – but no overall reduction in mortality. The risk reduction found in the observational studies looked at was very modest.

“An emphasis on ‘high-fat’ is very misleading as only one of the two clinical trials, the PREDIMED study, did provide information on the actual fat intake and there was no difference in fat intake between those on a Mediterranean diet and those on the ‘low-fat’ control diet. Based on the clinical trials included, which are normally considered the gold-standard of evidence, it is not possible to assess the impact of fat intake.

“Many of the observational studies do not provide enough detail on fat intake to investigate how it affects health. The statement “a healthy diet can include ‘a lot of fat’” is therefore not really supported by the study itself, and it is difficult to understand how the PREDIMED study is used to support such a claim (see ‘total fat (% E)’ and ‘saturated fatty acids (% E)’ rows in table S7 on page 28 of the PREDIMED supplementary information at http://www.nejm.org/doi/suppl/10.1056/NEJMoa1200303/suppl_file/nejmoa1200303_appendix.pdf).

“The Mediterranean diet is a type of diet most nutritionists would consider to be healthy: high intakes of fruits, vegetables, cereals and fish, moderate intakes of red wine and dairy and low intakes of red meat and meat products. Any beneficial effect observed is more likely due to the adherence to such a dietary pattern.”

Dr Elizabeth Lund, Independent Consultant in Nutrition and Gastrointestinal Health, and former Research Leader at The Institute of Food Research, said:

“This paper provides some interesting insight into the potential benefits of a “Mediterranean” type diet in reduced risk of chronic disease. The study is an attempt to synthesis results from previous published studies, which the authors recognise is difficult due to the variability as to what is a Mediterranean diet.

“The results discussed mostly come from observational studies where diet has been assessed in large cohorts of people to see what diseases they succumb to later in life. This is particularly true of the cancer studies as most diet related cancers take decades to develop and running a classical clinical intervention trial is generally not feasible.

“The title of the paper needs to be interpreted with care. The definition of a Mediterranean diet used for the selected studies may not have specifically involved a low fat element but any effect of excess calories leading to people being overweight will have been factored out by the statistical analysis in individual studies. Being overweight is a well recognised risk factor for certain cancers such as colorectal cancer.”

‘Effects on health outcomes of a Mediterranean diet with no restriction on fat intake: A systematic review and meta-analysis’ by Hanna E. Bloomfield et al. published in Annals of Internal Medicine on Monday 18 July 2016.  

Declared interests

Dr Gunter 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 Elizabeth Lund: “I have no conflicts of interest in relation to this study. I was previously a Research Leader at The Institute of Food Research in Norwich and now hold an Honorary Senior Lectureship at The University of East Anglia (Department of Biological Sciences).”