Researchers have developed a novel way to detect whether a person follows a Mediterranean diet using a blood test and used it to show that a Mediterranean diet is associated with lower risk of type 2 diabetes. Unit PhD student Jakub Sobiecki and colleagues present their findings today in the open access journal PLOS Medicine.

Why measure the Mediterranean diet objectively?

The Mediterranean diet is a dietary pattern typically characterised by high consumption of vegetables, legumes, fruit, nuts, grains, fish and seafood, virgin olive oil, and moderate intake of meat, dairy, and wine. Earlier research has shown that people who self-report that they follow a diet that is closely aligned with the principles of the Mediterranean diet have a modestly lower risk of type 2 diabetes.

However, the subjectivity of self-reports makes that link uncertain, as other dietary research indicates that most people struggle to remember precisely and correctly report what and how much they normally eat and drink. Until now, the potential link between a Mediterranean diet and type 2 diabetes risk has not been evaluated using objective biological indicators—biomarkers—of adherence to the diet.

To address this senior authors Professor Nita Forouhi and Professor Nick Wareham at the MRC Epidemiology Unit led a team from Europe and Australia that developed a novel biomarker-based indicator of a Mediterranean diet.

Objective measurement of the Mediterranean Diet on an EPIC scale

There is no single biomarker that can be used to measure adherence to dietary patterns such as the Mediterranean diet, instead multiple biomarkers – for example vitamins or fatty acids circulating in the blood – must be analysed.

Unit PhD student Jakub Sobiecki, who was first author on the paper, said:

Investigations of the links between diet and risk of diseases can often be enhanced by using objectively measured biomarkers to address the limitations of using dietary intakes self-reported by study participants. Some nutrients and foods have specific blood or urinary analytes which can be used for this purpose. However, it has been less clear how to apply biomarkers to study overall diets.

Our research offers a novel approach to combine multiple biomarkers as a measure of following the Mediterranean diet. It enabled us to study the link between this dietary pattern and the risk of new-onset type 2 diabetes in a more robust manner than in prior research.”

The researchers first analysed blood samples from the Medley clinical trial of 128 people in Australia who had been assigned at random to follow either their usual diet or the Mediterranean diet for six months. They found that a composite score derived from the blood levels of 24 fatty acids and 5 carotenoids could be applied to predict whether participants were assigned to and following a Mediterranean diet.

Next, the biomarker score of adherence to the Mediterranean diet pattern was applied in the EPIC study of 340,234 people living in eight European countries, of whom 9,453 developed type 2 diabetes during follow-up and had relevant biomarkers measured. Comparing them with 12,749 participants who remained free of type 2 diabetes, the researchers found that people whose biomarker score indicated greater adherence to a Mediterranean diet were less likely to develop type 2 diabetes.

Have the benefits of the Mediterranean diet been underestimated?

For comparison, the researchers also asked participants to self-report their diet. They found that using the biomarker score identified a stronger link between the Mediterranean diet and reduced risk of type 2 diabetes than when self-report was used. This suggests that previous self-report-based studies may have under-estimated the association.

Based on these findings the researchers argue that even a modest improvement in people’s adherence to a Mediterranean diet could meaningfully reduce the incidence of type 2 diabetes. However, they also point out that additional research will be needed to confirm and extend these new findings since currently it is unknown to what extent the biomarker score is specific for the Mediterranean diet.

Professor Forouhi said:

Our research combining information from a dietary clinical trial and a large cohort study to identify and apply blood biomarkers for a dietary pattern is exciting and should stimulate development of improved methods to study diet-disease associations which are typically limited by reliance on subjective recall of eating.”

Read more

• Sobiecki, JG  et al. A nutritional biomarker score of the Mediterranean diet and incident type 2 diabetes: Integrated analysis of data from the MedLey randomised controlled trial and the EPIC-InterAct case-cohort study. PLOS Medicine; 27 April 2023; DOI:10.1371/journal.pmed.1004221