You told you that you should run in the first place? You don't want to run, don't run. Walk, bike, swim, do something else. For me, running makes my body happy. Swimming makes it miserable. So I run, I don't swim.

Your body was meant to do things, so use it in a way that makes all of you happy. Rest is also "doing something", so make sure you do that too.

Happy doing!

Actually, I look at it as there being five components (in no specific order): cardio, flexibility, strength, diet and nutrition. So yeah, the what food you eat as well as how much of it matters too.

I've also heard that cardio isn't important, from a yoga source as well. I think there are shades of interpretation to that statement, that it's not so cut and dry. Cardio is necessary to burn off excess calories taken in, so with the proper intake of food, according to ayurveda, cardio could be seen as unnecessary. The niyama of tapas deals with creating heat and perseverence, which is closely related the endurance and calorie burning effects of cardio. An active asana practice, if that's how you choose to practice, could include a cardio element as well.

Point is, I believe the reasons behind needing the cardio element in your life as already included in the eight limbs of yoga, just not explicitly described as such. But don't ask me, I run because I tend to be kapha and need more movement in my life, and I tend to overeat when left to my devices. But understand it's the running that I need, not just any old cardio, because of how running itself affects me.

So, hope that made some sense. I think it's best to look at the big picture of who you are and how you operate, and then look to the yogic "rules" to decide what's best for you to do.