Congrats on the gains you have made in your health! Quitting smoking will make you feel better and run faster.
Gaining weight when quitting smoking is a common concern. However not everyone gains weight after quitting. Some people do, but usually only five or six pounds. Two things seem to cause this weight gain. First, your body metabolism slows down when you quit, so you don't need as much food as when you were smoking. Second, you may use food to replace cigarettes and end up eating a bit more than before.
Here are some tips to prevent weight gain:
-Continue to eat healthy and exercise
-Since food may taste better after you quit, you may want bigger helpings. Try to eat the same amount as usual.
-Nicotine withdrawal can cause constipation. Drink lots of fluids.
-Moderate your use of alcohol. Keeping your hands busy with smoking may have slowed up your drinking before. Without a cigarette, your rate and number of drinks may increase along with your weight.
I can't believe that you can run 10 miles at a go and you still smoke. WOW! I take it that you're not a heavy smoker then?
Weight gain is probably inevitable at the start of a quit, but it is fairly easy to keep in check. It should be even easier for you since you exercise so much now. You may not even gain anything since you are active now while you a smoker. Most smokers do not exercise much if any at all, at least the smokers that I know of. I gained 9 pounds when I quit, and have leveled out. I'm 15 pounds over my ideal weight, and if I'd exercise more I could probably bring it down. I'm not too concerned about it though.
From the determination I'm reading in your post, I do not think you are going to have any problem keeping your weight in check once you quit smoking. You didn't say how much you smoke though. Are you mentally prepared for you quit journey? If you haven't done so yet, I'd suggest that you go through the "my program" at the top of the page. It will help prepare you for your quit journey.
Long story short, I'm going to stop smoking in a couple of days. I've been wanting to stop for some time, but one thing has been keeping me from taking the plunge: weight gain. A couple of years ago I decided I was tired of being overweight and wanted to do something about it, so I took up running. I hadn't done any exercise in at least 10 years, so it was very difficult at first. I couldn't even run 1/4 of a mile without running out of air. That was two years ago. Since then, I've worked really bloody hard and built up my strength to the point where I can now run 10 miles in one go with no stopping at all. I average about 25-35 miles of running per week. I've lost almost 30 pounds in the past couple years, which is a huge achievement for me.
As you can tell, I'm frightened of putting the weight back on when I quit smoking. As I am a runner, and providing I keep up my fitness regime, do I stand a good chance of keeping the weight down or, at least, only gaining a minimal amount? I'm definitely going to quit smoking, I'm just wondering how much harder I'll have to work to keep the weight down or at least prevent me from gaining more. I generally eat quite healthily as I'm a vegetarian.
Thanks for any advice, tips or experiences anyone may have to share :)
I take it that you're not a heavy smoker then? 
