How come all those tv 'experts' who are not doctors talk about health? Can I believe them?

Great personalities. Great personalities and physical attractiveness are usually prerequisites to being a tv "health expert". Some truly are experts in their field and have good clinical experience... But the key thing to remember is that they don't know you. Health is a very individual thing. And every person is different. Find a good, caring, diligent doctor - and they will be your "personal expert" on health.