Kicking cigarettes, say addiction researchers, is as tough as quitting heroin. So it's no surprise that more than 75 percent of smokers who quit are puffing away again one year later.

Weight gain is a major reason these "quitters" give for relapsing, says psychologist Neil Grunberg of the Uniformed Services University of Health Sciences in Bethesda. Smokers weigh, in general, seven to eight pounds less than non-smokers. Those who quit smoking put on an average of five to seven pounds, he says, although the range of weight gain can be from zero to 30 pounds or more.

The nicotine-weight connection may be particularly pronounced in women, says Grunberg, whose current studies with animals indicate that nicotine causes greater body weight changes in females than in males. This may be one reason why teen-age girls -- among the most weight-conscious section of the population -- are the fastest growing group of cigarette smokers.

"The relationship is clear -- nicotine decreases body weight," Grunberg says. "Until recently the reasons for it reducing weight have not been clear ."

But now, in a series of recent laboratory studies on rats and on humans, Grunberg and his colleagues report that nicotine intake decreases the consumption of sweet foods. Take away the nicotine -- be it for rats or humans -- and the amount of sweet foods eaten increases in direct proportion to a rise in body weight, Grunberg found.

So it's not just that the orally fixated smoker trades in the gratification of cigarettes for the pleasures of eating, Grunberg says, but that sugar is a particular problem for those trying to kick the nicotine habit.

Similar findings surface in a broader study. When Grunberg and colleague David Morse correlated cigarette consumption and food intake from 1964 to 1977 -- the time following the U.S. Surgeon General's first report on the health hazards of cigarettes -- the same inverse relationship between cigarettes and sugar emerged. Their findings, set to be published later this year in the Journal of Applied Social Psychology, reveal that as cigarette consumption dropped, sugar sales increased.

No one knows yet how nicotine exerts these effects. "We believe that nicotine alters the preference for sweet-tasting foods," Grunberg says. "We don't think that it alters how the foods taste." His hunch is that nicotine, which is a very powerful drug, affects the availability of glucose in the body, and this in turn changes the desire for ". . . if you restrict the type, but not the quantity, of food around the ex-smoker you may be able to control body weight gain . . ." sweets. Other known effects of nicotine include raising the blood pressure, increasing the heart rate and stimulating the sympathetic nervous system -- the part of the nervous system that releases adrenalin. As a result, nicotine also constricts peripheral blood vessels (those farthest from the heart) and increases respiration rate.

To further pinpoint the relationship between smoking cessation and the desire for sweets, Grunberg conducted two more animal studies. This time, laboratory rats received a diet of only bland food and water. Nicotine still decreased body weight, but when the drug was stopped, the animals did not show the abnormal weight gain associated with a diet containing sweet foods.

"These findings suggest that if you restrict the type, but not the quantity, of food around the ex-smoker," Grunberg says, "you may be able to control body weight gain -- not by purposely dieting, but by just throwing all of the sweets out of the house."

Could a low-calorie sugar substitute quell ex-smokers' desire for sweets? Possibly. Says Grunberg: "That should probably satisfy their craving for sweets."

Recent results from these studies were presented in August at the American Psychological Association's annual meeting. Other findings appeared in the scientific journal, Psychopharmacology.

"If we can control the body weight gains," Grunberg says, "we may be able to help encourage people to quit smoking."

In the meantime, Grunberg and his colleagues are beginning to investigate sex differences in cigarette smoking.

Where once cigarette smoking was mostly a male habit, today some 24.5 million women, ages 20 and older, smoke. That's five million more female smokers than in 1965. As a result, national lung cancer mortality rates for women now approach the figures for breast cancer and in some states are surpassing those of breast cancer.

There is some evidence, based on animal studies, that nicotine causes greater body weight changes in females than in males. The suggestion is that nicotine may exert a double effect: it decreases body weight more in females, then results in a greater body weight increase during withdrawal.

"If this finding holds up," Grunberg says, "we will explore both the behavioral and the biological effects of smoking and nicotine on males versus females."

Any differences "could have implications for both smoking cessation and for how nicotine exerts its effects," he says. The next step, Grunberg says, is to look at the subtle biochemical reactions in the body that may account for the increased desire for sweets.