We now know that grilling meats, poultry and fish at high temperatures (which defines grilling) can cause carcinogenic compounds (heterocyclic amines, or HCAs) to form on the food. The recommendation is to grill less often, but there is an additional way to reduce exposure.
Adding thyme and rosemary to a marinade seems to inhibit the formation of these harmful substances. Soak the meat for an hour or more then grill at moderate temperatures, not high. The antioxidants (cancer-fighting compounds) in the spices can cut the HCAs by up to 87%, according to research by Kansas State University.
So, enjoy your grilled food, but consider a tasty marinade to protect yourself from carcinogens.