Does it have to be a NANDA approved dx?
I don't know that I would say that activity intolerance is r/t sedentary lifestyle, that sounds more like a nutritional thing to me too. I think of activity intolerance more as an "unable to complete ADLs" sort of thing... ?
Among the dx for obesity my nursing care plan includes, I pulled out the following:
Nutrition, imbalanced: more than body requirements r/t excessive intake
Nutrition, readiness for enhanced (might be a good one for a teaching plan?)
Self-concept, readiness for enhanced
Health-seeking behaviors r/t absence of aerobic exercise (might be another good one?)
Knowledge, readiness for enhanced
Body image, disturbed r/t eating disorder OR r/t negative self-image
Hope this helps. Good luck!