“Heath and Fitness” is a pretty serious topic bro… unless your friend knows what he/she is doing, it’s not wise to start one, just because we can generate traffic/revenue from this.
1. Make sure the information is checked thrice properly before publishing.
2. Always keep disclaimers that like Practo does:
“Disclaimer : The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.”
This “Health” or “Fitness” niche is similar to any other niche out there, just blog properly, you’ll get traffic/audience/revenue as long as you provide quality information.