Consumption of vegetables more than eight times a week, of fish more than three times a week, and of legumes more than once a week, seemed to be particularly protective.
The researchers said the Mediterranean diet tended to be well balanced and full of foods which contained beneficial vitamins and minerals.
In particular, the diet was high in antioxidants, which help to keep tissues - including those in the lungs - healthy.
Fatty acids from fish were known to help cut potentially damaging inflammation.
The Thorax study continues: "Further studies are needed to better understand the mechanisms of this protective effect and the most relevant window of exposure."
-Med diet 'cuts baby asthma risk'