This study, from the British Medical Journal, looked at the prospective cohort of 121,700 US female nurses ages 30-55 and prospectively collected data on demographics, lifestyle, and disease.

http://www.bmj.com/content/349/bmj.g6674

From the 4,676 available history/blood samples, they were able to find an association with the Mediterranean diet and longer telomeres in white blood cells, which we generally consider to be a biomarker for longevity and health.

Despite the limitations of the quantitative PCR telomere measurements, recall bias, and statistical confounding, they appeared to conclude what they were looking for.

That is to say, eating a Mediterranean diet was highly correlated with longer telomeres even after correcting for the big confounding variables of age, BMI, smoking, physical activity and total caloric intake.

What’s in that diet according to this paper by Crous-Bou et al?

“Alternate Mediterranean Diet score includes the following nine components: vegetables (excluding potatoes), fruits, nuts, whole grains, legumes, fish, monounsaturated:saturated fatty acid ratio, red and processed meats, and moderate alcohol intake.”