WASHINGTON (AP) — Scientists say they've finally discovered why smokers tend to gain some weight when they kick the habit.

It turns out that nicotine can rev up brain cells that normally signal people to stop eating when they're full, researchers report in Friday's edition of the journal Science.

The weight connection isn't huge: On average, quitters gain less than 10 pounds. Still, it's a worry that many smokers cite when asked why they don't try to quit. Now the question is whether the discovery might lead to better treatments to help them quit without worrying about weight.