The scientific consensus is that nicotine, the addictive substance in tobacco, typically suppresses a person’s natural appetite and increases metabolism. This dual action is why people who smoke often have a lower average body weight than non-smokers. Quitting smoking is frequently associated with an increase in hunger and subsequent weight gain.
How Nicotine Suppresses Hunger Signals
Nicotine acts as a powerful appetite suppressant by directly affecting the brain’s control centers for hunger and satiety. It functions as an agonist, binding to specific receptors on nerve cells known as nicotinic acetylcholine receptors (nAChRs). These receptors are widely distributed, but their activation in areas like the hypothalamus is directly linked to appetite regulation. When nicotine binds to nAChRs in the arcuate nucleus of the hypothalamus, it increases the activity of neurons that produce pro-opiomelanocortin (POMC), a peptide associated with feelings of fullness. Nicotine also influences the release of neurotransmitters, including dopamine and serotonin, which contribute to a sense of well-being and satiety, further reducing the drive to seek food. The effect extends to appetite-regulating hormones, such as ghrelin, which nicotine can suppress, resulting in decreased hunger pangs.
Nicotine’s Impact on Energy Expenditure
Beyond its effects on appetite, nicotine also influences the body’s energy balance by acting as a stimulant. This stimulating effect leads to an increase in the basal metabolic rate (BMR), which is the amount of energy the body burns while at rest. Nicotine can increase the body’s 24-hour energy expenditure by approximately 10%, translating to burning about 200 more calories per day than a non-smoker. This increase in energy use is partly due to thermogenesis, the process of heat production in the body, which is stimulated by nicotine. Nicotine acts like a sympathomimetic agent, promoting the release of compounds like norepinephrine and epinephrine that increase heat production in fat tissue. This mechanism increases the breakdown of fat, a process called lipolysis, and stimulates the expression of uncoupling protein 1 (UCP1) in adipose tissue, resulting in a rise in basal metabolism.
The Biological Reason Quitting Causes Increased Appetite
When a person stops smoking, the steady flow of nicotine that has been artificially suppressing appetite and boosting metabolism abruptly ceases. This removal of nicotine’s influence triggers a rebound effect in the brain’s appetite-regulating circuitry. The nAChRs in the hypothalamus are no longer stimulated, which reverses the signaling that promoted satiety, leading to an increase in hunger signals and food intake. Simultaneously, the metabolic rate begins to slow down, returning to a normal, healthier baseline. The body no longer benefits from the 10% caloric burn boost provided by nicotine, meaning it requires fewer calories to maintain the same weight. If a person continues to eat the same amount of food they consumed while smoking, they will quickly create a caloric surplus, leading to weight gain. The absence of nicotine in the reward centers of the brain can also increase the rewarding value of other dopamine-inducing substances, like high-calorie foods, leading to increased cravings and contributing to weight gain.
Managing Weight Changes After Stopping Smoking
The average weight gain after stopping smoking is modest, typically ranging from four to five kilograms in the first year, with most of that gain occurring in the first three months. Managing this change involves a focus on lifestyle adjustments that counteract the drop in metabolism and the increase in appetite. Increasing physical activity is an effective strategy, as regular exercise can help maintain a higher metabolic rate and burn the extra calories that nicotine no longer handles. Controlling appetite can be achieved by being mindful of food choices and portion sizes. Stocking up on low-calorie, high-volume snacks, such as fruits and vegetables, and staying well-hydrated can help satisfy hunger and oral fixation without a large caloric cost. It is important to remember that the health benefits of stopping smoking far outweigh the risks associated with the average amount of weight gained.