what is the best way to become a wellness coach? Is cerification a must?

I am a veterinarian and spin instructor. In my "previously life" through school I instructed everything from aqua aerobics to step aerobics. I am maxing out in my educational budget so want to prioritize my next phase in life. I am very interested in nutrition and have a fair amount of base knowledge but would like to help others. I have been investigating the Wellcoaches program as well as the IIN program. Any thoughts on how well these certifications may be accepted in the larger medical and fitness community?