Weight gain that occurs without changes in diet or decreased physical activity indicates an underlying physiological imbalance. In women, hormonal fluctuations at each stage of life (cycles, pregnancy, perimenopause) multiply the potential mechanisms. Identifying the precise cause remains the only way to act on the right lever, rather than restricting calories without results.
Antidepressants and weight: an underestimated factor in women
Articles on unexplained weight gain often list stress, thyroid issues, or sedentary behavior. One factor is rarely detailed: the effect of antidepressants on fat storage. Women are, however, more frequently affected by these long-term prescriptions.
A British analysis involving nearly 300,000 patients followed over ten years highlighted an approximately 21% increase in the risk of clinically significant weight gain among those on antidepressants. The risk of moving to overweight or obesity increased by about 29%. The effect can persist for up to six years after starting treatment.
The REGICOR cohort study, published in Spain, confirms this trend: individuals who have consumed antidepressants, even intermittently, show a higher weight gain than those who have never taken them, over six years of follow-up. In the face of unexplained weight gain in women, checking the list of current treatments is therefore a logical first step.
Not all molecules are equal. A trial published in Annals of Internal Medicine (over 183,000 adults) shows that bupropion is associated with significantly less weight gain and a lower risk of gaining 5% or more of body weight compared to sertraline. Discussing the choice of molecule with the prescriber can make a measurable difference on the scale, without compromising treatment.
Cortisol, insulin, and inflammation: the metabolic triangle
Prolonged stress is not limited to a feeling of tension. It triggers chronic secretion of cortisol, a hormone that promotes fat storage, particularly in the abdominal area. This mechanism is independent of caloric intake.
High cortisol also disrupts sensitivity to insulin. When cells respond less effectively to this hormone, the pancreas produces more. Excess insulin directs metabolism towards storage rather than energy use. The result: gradual weight gain, even with a balanced diet.
Chronic low-grade inflammation
Excess cortisol and insulin fuel a third factor: chronic low-grade inflammation. This silent phenomenon alters the functioning of adipose tissue itself, which becomes an active organ secreting pro-inflammatory molecules. The cycle closes: the more inflamed the adipose tissue, the faster fat storage accelerates.
Acting on this triangle requires intervening upstream:
- Reducing cortisol spikes through sleep management (sleep deficit amplifies cortisol production and reduces leptin secretion, the satiety hormone)
- Limiting sharp fluctuations in blood sugar by favoring meals with moderate glycemic load, stabilizing the insulin response
- Incorporating anti-inflammatory food sources (omega-3s, cruciferous vegetables, spices like turmeric) to mitigate metabolic inflammation
Muscle mass and resting energy expenditure
Basal metabolism, that is, the energy expended at rest to maintain vital functions, largely depends on muscle mass. In women, this mass naturally decreases with age, and the decline accelerates from perimenopause due to the drop in estrogen levels.
Less muscle means fewer calories burned at rest. Without adjusting diet or physical activity, the differential accumulates. In a few months, this gap can represent several additional kilos of adipose tissue.
Muscle strengthening rather than caloric restriction
Reducing portions without preserving muscle mass worsens the problem. The body, deprived of energy, first draws from muscle. Basal metabolism drops further. Muscle strengthening protects metabolism where a restrictive diet degrades it.
Two to three weekly resistance sessions (free weights, bands, body weight) are sufficient to maintain or even increase muscle mass. The effect on body composition far exceeds that of cardio alone, which burns calories during exercise but does not change resting expenditure.
Sleep and hormonal regulation of weight
Sleep deficit directly affects two appetite-regulating hormones. The production of leptin (satiety signal) decreases, while that of ghrelin (hunger signal) increases. This double disruption leads to increased eating, steering choices towards foods high in sugars and fats.
Beyond appetite, insufficient sleep raises morning cortisol, reduces glucose tolerance, and promotes inflammation. These effects accumulate night after night. A regular, even moderate, deficit can significantly accelerate fat storage over several months.
- Aim for a regular sleep duration, with stable bedtimes and wake-up times, even on weekends
- Limit screen exposure in the hour before bedtime to preserve melatonin secretion
- Treat any potential sleep apnea, common and underdiagnosed in women, which fragments rest and amplifies metabolic disturbances
Weight gain without an apparent dietary cause rarely results from a single factor. Medication treatments, chronic cortisol, muscle loss, sleep debt: these mechanisms interact and reinforce each other. A targeted medical assessment (TSH dosage, fasting glucose, cortisol, review of treatments) allows for identifying the real levers and avoiding unnecessary dietary restrictions that often worsen the initial metabolic imbalance.