Nicotine is a naturally occurring psychoactive substance associated with lower body weight, meaning users are typically slightly thinner than non-users. This effect results from nicotine influencing both the “calories in” side, by suppressing appetite, and the “calories out” side, by increasing the rate at which the body burns energy. Because these effects are temporary, the link between nicotine use and reduced body mass ceases upon withdrawal.
How Nicotine Influences Appetite and Food Intake
Nicotine acts as an anorectic agent, suppressing appetite and reducing overall food intake. This effect is mediated by nicotine’s binding to nicotinic cholinergic receptors in the brain, which regulate reward and homeostatic signals. Nicotine specifically interacts with neural pathways, such as those in the hypothalamus, that control feelings of hunger and fullness.
Nicotine alters the circulating levels and effectiveness of appetite-regulating hormones like leptin and ghrelin. Nicotine appears to enhance leptin’s suppressive effect on appetite while tempering ghrelin’s ability to stimulate food intake. This hormonal modulation helps explain why nicotine can reduce the desire for sweet or high-calorie foods, contributing to lower caloric consumption.
Nicotine’s Effect on Resting Metabolism
Nicotine also increases the body’s energy expenditure, even while at rest, by acting as a sympathomimetic agent that stimulates the nervous system. This stimulation causes the body to release neurotransmitters like norepinephrine and epinephrine, which increase metabolic activity. This nervous system activation leads to an increase in the basal metabolic rate (BMR).
Nicotine can raise the BMR by approximately 7% to 10%, or roughly 200 calories per day, by promoting heat production, a process called thermogenesis. It also increases lipolysis, the breakdown of fats, and stimulates the expression of uncoupling protein 1 (UCP1) in fat tissues.
This higher rate of calorie burning helps maintain a negative energy balance, which is the mechanism by which nicotine users tend to weigh less.
The Reversal: Weight Changes After Quitting Nicotine
When a person stops using nicotine, the weight-suppressing effects immediately begin to reverse, which is the primary reason weight gain is a common outcome. The average weight gain is typically modest, around 4 to 5 kilograms (9 to 11 pounds), within the first year of abstinence, with the most significant increase often occurring in the first three months. This weight change results from the combined cessation of nicotine’s metabolic and appetite-suppressing actions.
The resting metabolic rate, which was elevated by nicotine, slows down and returns to a normal baseline level. This metabolic deceleration means the body burns fewer calories each day, creating a daily calorie surplus if food intake remains the same. Simultaneously, the removal of nicotine’s appetite-suppressing effects leads to a return of normal hunger signals and often a temporary increase in caloric consumption, sometimes exceeding 200 more calories per day.
Behavioral factors also contribute significantly to the weight increase. Many former nicotine users substitute the oral fixation and hand-to-mouth action of nicotine delivery with eating, often choosing high-calorie snacks. This combination of a slower metabolism, increased appetite, and a behavioral tendency toward greater caloric intake results in a positive energy balance that drives the weight gain observed after cessation.