To Guest smoking yuk, it's easy for a non smoker to give advice, but, it carries little weight with the addicted.
When I quit (after 47 years) 6 years ago Monday next, I weighed 14 stone. Today, I weigh 14 stone.Quitting is only part of the process, you MUST also do some serious behavior modification.
I don't believe that about nicotine speeding up your metabolism; what I think it is, simply that the nicotine was used to fill a void in our psyche, and, when we quit, the handy thing is food. Neither will ever really fill that void, but, our ability to fool ourselves is so powerful that denial is our way of dealing with the addiction.
The only time I crave a smoke is times such as this; I would kill for a weed, but, I know that when I get off this subject, the craving will go away. It really is all in your head.