The short version
Weight gain in winter is common, well-documented, and partly biological. The reasons involve more than comfort food and less exercise. Hormonal shifts tied to reduced daylight, appetite signals with evolutionary origins, and disrupted sleep patterns all contribute in ways that most standard advice does not address. Understanding what is happening biologically makes it easier to respond thoughtfully rather than reactively.
This Is Not Just About Willpower
Every winter the same narrative appears: we move less, eat more, and the weight creeps up. The framing is almost always behavioural, as though the solution is simply more discipline against the cold. The biology tells a more interesting and more useful story.
An Australian cohort study tracking daily weight across twelve months in Adelaide found that winter was one of two key periods of weight gain for Australian adults, alongside the Christmas and New Year period. Importantly, those who gained the most weight overall gained the largest proportion of it during winter (Hennis et al., 2023). This is a seasonal metabolic pattern that operates in the Australian context, and it deserves a clinical response rather than a moral one.
The Evolutionary Driver
The biological push toward weight gain as daylight shortens has ancient origins. In environments where food became scarce in colder months, storing energy in autumn and winter was a survival advantage. The mechanisms that supported this are still present in our physiology: reduced sunlight triggers hormonal and neurochemical changes that increase appetite, reduce activity drive, and favour fat storage.
We no longer live in those food-scarce environments. We live in temperature-controlled buildings with year-round food availability. But the biological signals did not get the memo. Understanding that some of what feels like a failure of willpower in winter is a deeply conserved physiological programme changes the clinical frame considerably.
Melatonin, Appetite, And Shorter Days
Melatonin, the hormone that regulates our sleep-wake cycle, increases with reduced daylight. In addition to its role in sleep timing, melatonin is associated with increased appetite, and its rise through the shorter days of winter is one mechanism through which the body is pushed toward higher caloric intake. This operates largely outside conscious awareness. You do not decide to be hungrier in winter. The hormonal environment shifts and appetite follows.
Reduced sunlight also affects serotonin production, which has direct effects on both mood and carbohydrate craving. Serotonin is synthesised from tryptophan via a pathway that is sunlight-dependent. As serotonin drops in winter, the brain seeks carbohydrate-dense foods as a rapid route to tryptophan uptake and serotonin restoration. The cravings for bread, pasta, and sweet foods that many people notice in winter are not arbitrary. They are the brain seeking neurochemical equilibrium through the fastest available route.
Reduced Movement: More Than Exercise
The movement drop in winter is real but often underestimated. Most people focus on formal exercise, which may reduce modestly. The bigger effect is on incidental movement: the walk to the train in the evening, the lunchtime steps, the weekend outdoor activities. Cold mornings and shorter daylight hours reduce all of these, sometimes substantially, without any single decision being made. The cumulative effect on daily energy expenditure is meaningful.
For people managing weight with GLP-1 medications, this seasonal reduction in movement is clinically relevant. These medications work in part through appetite regulation, but the metabolic benefits of maintaining lean muscle mass through regular movement do not pause for winter. Resistance training indoors, and protecting at least some daily step volume even in cold weather, remains worthwhile.
Sleep Disruption And Appetite Hormones
Winter disrupts sleep patterns for many people through multiple mechanisms: later sunrise meaning some people sleep longer and shift their rhythm, artificial light extending evening wakefulness, and in some cases mood changes associated with reduced daylight shortening overnight sleep. Even modest sleep restriction raises ghrelin and suppresses leptin, increasing appetite and particularly cravings for high-energy foods. Winter sleep disruption is a meaningful contributor to the seasonal weight pattern, and it is one that receives relatively little clinical attention.
The Comfort Eating Mechanism
Comfort eating in winter has a physiological basis that is separate from habit or emotional vulnerability, though both of those also contribute. Cold temperatures activate the body’s thermoregulatory systems, which have some increased energy demands. The brain also associates warmth with safety and satiety in ways that are partly learned and partly hardwired. The combination of reduced serotonin, increased melatonin, lower ambient temperature, and decreased daylight creates a genuine neurochemical environment that increases drive toward calorie-dense food.
This does not mean that comfort eating in winter is inevitable or unmanageable. It means that managing it requires understanding the mechanism rather than applying generic restraint. Adequate protein at each meal buffers the blood sugar swings that amplify carbohydrate craving. Warm, protein-rich foods, soups with legumes, stews with lean protein, eggs in the morning, satisfy both the thermoregulatory and appetite signals more durably than carbohydrate-heavy comfort foods that produce a rapid rise and fall in blood sugar.
For People Already Managing Their Weight
For anyone in an active weight management programme, winter is worth approaching as a distinct season rather than an interruption to normal. The strategies that work best in summer often requires adjustment in winter: higher protein targets to maintain satiety in the context of increased appetite signalling, explicit protection of sleep timing, resistance training maintained indoors, and realistic expectations about the scale, which may reflect fluid and glycogen shifts that are entirely normal.
If you are using medication as part of your management, winter is a reasonable time to check in with your clinical team about how the seasonal pattern is affecting your experience. The medications that support appetite regulation work with the biological environment, and winter creates a more challenging biological environment. That is a clinical conversation worth having rather than a private source of discouragement.
We cover the broader biology of weight gain, including hormones, genetics, sleep, and medications, in our What Causes Weight Gain? article.
This article is general information only and not personal medical advice. Obesity assessment and treatment decisions should be made with a qualified health professional after individual clinical assessment. Not all treatments are suitable for every person.
Looking Forward
Winter weight gain is real, it is partly biological, and it is not a character failing. The people who navigate it best are usually not the ones with the most willpower. They are the ones who understand what is driving the seasonal pattern and make a few targeted adjustments rather than attempting to override the entire biological signal through restriction alone.
If winter has historically been a difficult period for your weight management, a clinical conversation that takes the seasonal context into account is a more useful starting point than another attempt at the same approach. That conversation is one we are ready to have at Alevia.
Evidence Notes
Hennis, K., et al. (2023). Weekly, seasonal, and festive period weight gain among Australian adults: a cohort study. Obesity, 31(7), 1936-1947. https://pmc.ncbi.nlm.nih.gov/articles/PMC10375309/
Yanovski, J.A., et al. (2000). A prospective study of holiday weight gain. New England Journal of Medicine, 342(12), 861-867. https://pubmed.ncbi.nlm.nih.gov/10727591/
