A small study presented at the European Respiratory Society International Congress found what you likely knew, if you are old enough to remember when smoking was common; smoking made people thinner.
But the paper says people don't gain weight after while quitting because of oral smoking habits being replaced by eating ones, they speculate about an effect on levels of the hormone ghrelin (also known as the hunger hormone).
Smoking and its cessation are related to weight change, as noted. Those who manage to stop smoking sometimes increase their weight, while current smokers are less likely to be obese than non-smokers. In the past it was assumed that female adolescents even started and continued smoking for body weight management. Post smoking cessation weight gain (with a mean weight gain pf around 10kg over 5 years), is listed on surveys by women as a reason not to quit and a common reason to relapse. Of course, it's an addiction, people lie about why they do it, but some scholars have still sought to solve the weight gain problem rather than the addiction one.
The aim of the work by Dr. Konstantina Zachari of Harokopio University Athens, and colleagues, was to examine the acute effect of smoking and its abstinence on dietary intake, subjective feelings and hormones related to appetite. A small randomized crossover study was conducted, involving 14 healthy males who participated in two trials after overnight abstinence from smoking and food: the C-cig, where they smoked two cigarettes of their brand and the S-sham (control) where they held the cigarette as smoking without lighting it. Each trial lasted 15 min and after 45 min participants ate ad libitum (freely) a variety of snacks.
Dietary intake and at standard time points (t=0 mins, t=60 mins, t=150 mins) appetite feelings (hunger, satiety, desire to eat) and craving for smoking were recorded. Blood samples were collected and analyzed for various hormones including obestatin, ghrelin, GLP-1, CCK and insulin.
The researchers found that smoking had an acute effect on dietary intake, reducing it by 152 calories - a statistically significant result. There was no intervention effect for taste preference (sweet or salty foods) or macronutrient intake. An intervention time effect on plasma ghrelin concentration was found (of borderline statistical significance), with ghrelin's concentration being lower 60 min after S-sham, indicating more fullness and food consumption after the S-sham part of the study. There was no intervention effect for appetite feelings, obestatin, CCK, GLP-1 and insulin.
Dr Zacchari concludes: "In our small study, we found that smoking had an acute effect on energy intake that could be mediated by alterations in ghrelin levels. Further research is needed to investigate whether these results would be duplicated in a broader study population. We also need to investigate other potential biological mediators and ways to balance post-cessation weight gain in order to achieve higher smoking cessation rates and lower relapse rates."