5 Unexpected Things That Can Cause Weight Gain
When most people think about weight gain, they picture overeating or not exercising enough. But the reality is far more complex. Weight changes are influenced by dozens of biological, environmental, and lifestyle factors—many of which have nothing to do with willpower.
Importantly, none of these factors act in isolation. Each one works through multiple pathways—hormonal, behavioral, environmental, and social—so there’s rarely a single “fix.” If there were, my work as an obesity medicine physician would be much simpler, and many people wouldn’t be left wondering why their weight has changed despite healthy intentions. Understanding these layers can help identify the real drivers behind weight gain and open the door to more effective solutions.
1. Poor Sleep and Circadian Disruption
Getting less than 7 hours of quality sleep changes the balance of hunger hormones like ghrelin and leptin, making you feel hungrier during the day. But that’s only one part of the equation. Sleep deprivation also reduces insulin sensitivity, increases cravings for high-calorie foods, lowers energy levels for physical activity, and makes it harder to resist quick, convenient snacks. People who work night shifts or travel frequently across time zones face an added challenge: the body’s internal clock (circadian rhythm) is disrupted, affecting metabolism and fat storage patterns in ways that can persist even after schedules normalize.
2. Weight-Promoting Medications
Several prescription medications—including certain antidepressants, antipsychotics, insulin, steroids, and beta-blockers—can contribute to weight gain. The mechanisms vary: some increase appetite, others slow metabolism, cause fluid retention, or reduce energy levels, making it harder to stay active. In some cases, these effects are subtle at first but can lead to gradual, steady weight gain over time. If you notice changes in your weight after starting a new medication, it’s worth having an open conversation with your doctor. Adjustments are sometimes possible, but never stop or change a medication without professional guidance.
3. Alcohol
Alcohol’s calories are just the beginning of its impact on weight. Drinking can increase appetite, lower inhibitions around food choices, and disrupt normal fat metabolism, making it harder for your body to burn fat efficiently. Alcohol also interferes with sleep quality, which can indirectly affect weight by altering appetite regulation and energy levels the next day. Even moderate intake—just a few drinks per week—can add up over time, especially when combined with the extra snacks and meals that often accompany social drinking.
4. Parenting
Parenting changes nearly every aspect of daily life. Whether you’re caring for a newborn or managing the schedules of teenagers, the demands can mean less sleep, higher stress, fewer opportunities for physical activity, and more reliance on quick, convenience-based meals. These shifts are not just temporary—they can persist for years, subtly influencing metabolism and daily habits in ways that make weight maintenance more challenging. The combination of irregular routines, emotional demands, and limited self-care time can create a perfect storm for gradual weight gain, even when you feel like you’re doing your best.
5. Chronic Stress
Stress is complex, and its relationship with weight is far from a single “cortisol” story. While elevated cortisol is one piece, chronic stress also disrupts sleep, alters food preferences toward higher-calorie comfort foods, affects gut health, and reduces physical activity levels. It can change how the body stores energy, often promoting abdominal fat accumulation. Stress also has a behavioral component—over time, people may find themselves eating more frequently, snacking mindlessly, or skipping planned workouts. These overlapping effects can be subtle in the short term but meaningful over months and years.
If you’ve been frustrated by unexplained weight gain, you’re not alone. These factors are often overlooked, and most primary care visits don’t leave enough time to fully explore them.
A board-certified obesity medicine doctor can help identify your unique contributors and create an evidence-based plan—whether that’s adjusting medications, improving sleep, addressing stress, or using modern weight loss medications like GLP-1 receptor agonists.
