Hard to imagine anyone on a nutrition forum encouraging you to find a way to not quit smoking. That being said, lots of people smoke and still are obese, so I don't think the cigarettes are the problem unless you're smoking when you'd otherwise be eating. But the effects of smoking are so much worse than being too light, which might not be a health problem at all, that again, this is a nutrition site and I'm sure not going to suggest you do anything that would justify you're continued smoking -- lost too many family members to that curse, and it's a very slow painful way to go.
You can actually lose weight if you replace smoking breaks with going for a quick walk and drinking some ice water or tea and staying active, changing your diet, etc. it can help you change your whole lifestyle.