The more weight gained by smokers trying to quit, the less likely they are to light up again, researchers say.

But being heavier is healthier than continuing to smoke, one expert says."If I was a smoker, I definitely would want to quit smoking because that's the greater of the two evils," said Jack Henningfield, chief of the Addiction Research Center's clinical pharmacology branch in Baltimore.

A new study of 315 people found that long-term quitters gained a mean of 4.3 kilograms (9.46 pounds) more than non-quitters.

Among those who quit for at least six months, 22 percent put on nine kilograms (19.8 pounds) or more, said the study, published in the January issue of the American Medical Association's Archives of General Psychiatry. It did not provide further detail on amounts of weight gained among the groups.

Henningfield added: "It's possible that trying to diet while quitting smoking can complicate the withdrawal symptoms."

Researchers said many symptoms of nicotine withdrawal usually last four weeks, but the hunger, weight gain and craving persist for at least six months.