You can be overweight, yet still be relatively fit. Or you can be nice and slender, but have worrisome health issues. So what's the difference between being fit and being healthy.
Longevity, quality of life, and general well-being from a physical and mental point of view consists of many things, but there are a few factors that make up for most of it.
There are many more, but if you get these four right, managing everything else will be easy.
If you are a premium athlete, you may be fit from a purely cardiovascular point of view, but if you live off fast food, your body will be taking on board inflammatory, "food-like" products that will catch up with you in the medium and long term; perhaps even in the short term.
On the other hand, you could instead be living a relatively sedentary lifestyle, but live on an exquisite diet.
If I had to choose which is the more important -- what one eats versus the exercise one gets -- I would have to choose the former over the latter, but if you do find a way to get both right, your quality of life can be improved by orders of magnitude.
I can help you get both those key factors in your life in order.