Kosher

We have always kept kosher, to some degree. I am often challenged by friends who ask why do I need to choose this antiquated dietary system, when today there are many dietary systems, based on modern research, that are far healthier than kosher. Although kosher may have kept us healthier in the ancient world, why do we need to continue that today when there might, in fact, be even healthier systems? Could you please give me some food for thought to be able to answer them? (And myself!)