Claims for the health benefits of the typically Mediterranean diet high in olive oil, fish, and complex carbohydrates are common, if hard to substantiate.
Previous studies associated the TCF7L2 gene with regulation of blood sugar and pegged it as a diabetes risk gene. It has also been more loosely implicated in regulating lipid (fat) levels and in the development of cardiovascular disease. Results from a new large, randomised controlled study show that diet can affect these genetic associations.
'Our study is the first to identify a gene-diet interaction affecting stroke in a nutrition intervention trial carried out over a number of years in thousands of men and women', remarked Professor José Ordovás, director of the Nutrition and Genomics Laboratory at Tufts University, USA, who led the study.
The study was part of the wider PREDIMED trial launched in 2003 to investigate cardiovascular risk and nutrition in Spain. Over 7,000 participants were screened for the TCF7L2 variant and answered food questionnaires before and during the five-year study.
Results showed those carrying two copies of the genetic variant had raised levels of fasting glucose and lipids in their blood, were at an increased risk of developing type 2 diabetes, and also at an increased risk of stroke. Further investigation showed that these associations were affected by the kind of diet participants adhered to.
'Being on the Mediterranean diet reduced the number of strokes in people with two copies of the variant', said Professor Ordovás. 'The food they ate appeared to eliminate any increased stroke susceptibility, putting put them on an even playing field with people with one or no copies of the variant'.
In contrast participants in a control group on a low fat diet carrying two copies of the genetic variant were three times more likely to have a stroke compared to people with one or no copies of the genetic variant on the same diet.
The researchers suggest that components of the Mediterranean diet, such as the antioxidants in olive oil, may overcome genetic risk factors.
'Just remove some of the more negative aspects you have in your diet to include some of these components, and you can compensate for your risk', Professor Ordovás told Fox News.
Professor Keith Ayoob from the Albert Einstein College of Medicine, USA, who was not involved in the study, also supports the potential health benefits of the Mediterranean diet, remarking to MedPage Today that 'this is certainly a great start and this is the diet that's got the most leverage behind it because it has the most research'.
The study was published in the journal Diabetes Care.