camfer saidLive an active life so when you don't want to go to a gym,you can do something else that's fun and active.I haven't been in a gym in years. Yet I am still in good shape. Gyms aren't really necessary, depending on your goals.
Everyone should under go weight bearing / resistance exercise to increase their lean muscle mass, and keep their bones in good shape.
Being thin does not mean you're in shape, bone-wise, or cardio-wise. If fact, without exercise, you can succumb to sudden death because you don't realize you have advanced heart disease.
Doing HIIT, or rapid weight training, or playing soccer, basketball, or hockey, as they should be played, will increase your cardiac threshold. It's a critical part of any wellness plan. As few as 7 HIIT sessions, ever, can immediately change your EKG. As few as 7. HIIT is critical in cardiac health, if you can do it.
While stuff like running will keep you thin, it's high impact, and often leads to life long pain from those injuries.
Also, being thin doesn't protect you from type 2 diabetes. Only resistance training can do that, in as little as three sessions per week. The anaerobic exercise burns the sugar crystals up (lowers your A1-C), increases your glucose tolerance, and increases your insulin sensitivity.
I'm afraid you may be a bit deluded, actually.
In fact, AHA (American Heart Association) says that sudden death is MORE probable in runners. They aren't quite sure why, but, suspect it's from ongoing heart damage.