I am used to hearing things like "Marathons are bad for your health" from sedentary people... but today my little sister (who has run two marathons) told me that "I really don't recommend marathoning for you, it's so hard on your body... And unhealthy"

I'm not sure if she doesn't want me to run a marathon because it is her "thing" or if she has legitimate concerns.  I have entry to the 2015 NYCM because of 9+1 but this makes me wonder whether or not to claim my entry.

Feedback would be much appreciated!

I don't think we're doing it to be healthy, are we? Because I think for health, a moderate amount of running and some strength training would probably be better.  Marathons are hard on the body, as is training for marathons.  We choose to do many things that aren't necessarily good for us though.

^ This. I would say healthier than being sedentary, not as healthy as a more moderate amount of running. Full disclosure, I am not a doctor nor do I play one on TV.

Broken bones, pulled muscles, sore joints, GI issues, fatigue, cramps, constant hunger....meh, there's worse things you can do.  

Marathons hurt.

They wear the body down unlike anything I have ever done. (rugby, rowing, football, cricket cycling and I am sure there some others).

As others have already suggested, training for and running marathons (and by extension ultras) is a whole lot more healthy than sitting on the couch stuffing cheetos into your face, but  probably less healthy than a rounded program of running, other cardio and strength exercises.

Still do them though (2 road marathons and 4 "ultra length" (>= 6 hour) timed races)

Running a marathon was the dumbest thing I have ever done. So much so that I did it three times and likely will again. 

Agree with what others have said about "marathoning" compared to running for overall fitness and health. If you are training hard and really racing those marathons it is tough on the body. And I think it is mentally tough as well with balancing work, family, etc. with getting your workouts in.

I'm seriously thinking that next year will be the first year since 2007 that I won't race a marathon. I really feel worn out from the two cycles this year for some reason and am just enjoying some easy running right now. I have been asked by someone to help pace them to a sub 3:00 next fall but I'm not even sure about that. I have my eye on a race series in 2015 that has 1 mile to half-marathon distance races.

If nothing else it will mix things up for me.

Seriously though, for me, it depends on the intensity with which I ran the marathons. I've run on average 4 per year in the last 4 years. I would say that 3/4 of them were at moderate effort and 1/4 at hard effort (though LTH will say it surely wasn't an all out effort because I could start training again almost 2 weeks after each race). But this last month, after I ran 2 marathons 2 weeks apart, I've been having a really hard time recovering. I feel all wrong in many parts of my body (no injury, though) and I feel out of balance mentally and physically. I'm glad I did New York and I would do it again under the same circumstances, but I won't be racing hard two marathons so close to each other in the future. Too damageable... I think, though, that I could manage two slow 26 milers every month, with the proper weekly mileage to support it.

This, albeit 1+ hours slower than Lily.  I have run up to 12 marathons in one year (one double), no issues.  No injuries, nothing.  It depends on why you want to run one.  I just like the distance and don't race them as often as I run them.

Running the distance is no big deal and probably not bad for you if you've worked your way up to it sensibly. Running any distance hard as in a real race effort is probably bad for you because of the extreme stress it places on you. I've run 27 miles on hilly CT roads and thought nothing of it, and was back with normal training the next day. I've also raced 1000m so hard I couldn't walk without help after I finished. Ask not whether marathons are bad for you, but whether racing is bad for you.