Sometimes weight gain is easy to figure out. If you’ve changed your eating habits, added more dessert or processed foods, or have been spending more time on the couch than usual, you can typically blame those reasons if you gain a few pounds. But sometimes figuring out why you gained weight is trickier than that.

And while we’re living in unprecedented times, when stress levels are high and activity levels are lower due to quarantine and gym shutdowns, it’s normal to gain weight and it’s nothing to be ashamed of. But sometimes weight gain is more complicated than that. Weight gain is often caused by more than just the calories you eat and exercise (or lack thereof). The “calories in, calories out” approach is pretty dated when it comes to weight loss, so it makes sense that gaining weight is more complex than that too.

If you’ve gained weight and are having a hard time pinpointing the cause, keep reading below for five reasons that could be to blame.

1. Hormone issues

If you’re a woman and are dealing with unexplained weight gain, one of the first things you should check out are your hormones. Your hormones regulate so many important processes in your body, including your metabolism.

Hormone issues are pretty complicated though, so you typically need to get lab work done to really understand what’s going on. “There are five key hormones that can affect weight and when any of these happen individually or in combination it can trigger fat storage and weight gain,” according to Alisa Vitti, a functional nutritionist, hormone health expert and founder of hormone health care company FLO Living.

Those five hormone issues are:

• Insulin resistance: Insulin is a hormone that regulates your blood sugar. Insulin resistance is when your body can no longer respond to insulin properly.
• Low thyroid: Your thyroid is a major regulator of your metabolism and other key hormones. If your thyroid hormone is low, it can slow your metabolism, resulting in weight gain.
• Low testosterone: Testosterone is usually only associated with men, but women have it too and it plays a role in weight and metabolism.
• Elevated estrogen: Estrogen is an important hormone, but when estrogen levels are too high it can lead to a cascade of symptoms, including weight gain.
• Elevated cortisol: Cortisol is also known as the stress hormone, and when it stays elevated too long it can result in weight gain.

Several medical conditions that involve hormones can also be to blame for unexpected weight gain.

“When you have a diagnosed condition like PCOS, fibroids, endometriosis, ovarian cysts, PMS — it means that your body’s hormones are not functioning optimally. You could have excess estrogen, you could have elevated cortisol or insulin insufficiency all creating scenarios by which both your cycle as a whole becomes dysfunctional and weight becomes a problem,” Vitti says.

“The weight is the symptom of the hormonal imbalance and truly taking care of the hormonal issue is the best way to resolve weight discrepancy,” she adds. How you balance hormones depends on your personal situation and health care provider, but generally, it involves lifestyle changes like diet and exercise, and some doctors can prescribe you other things to help like hormone therapy.

2. Stress

Now that you know that hormones are an important part of the weight gain puzzle, you should know how stress can play a role. One of the ways it works? Stress affects hormones, which as we’ve seen can affect weight, not to mention your sleep too.

“Prolonged low-grade chronic stress is a huge factor for women especially,” Vitti says. “Managing invisible domestic work, managing children, working full time, taking care of elderly parents, remembering every detail and managing one’s own emotional reaction to current stressful events takes a huge toll on women’s adrenals.” Your adrenal glands produce the hormones that help regulate your metabolism, blood pressure and immune system, among other things.

Stress, and the habits that can result from stress, are part of a bigger picture that Vitti says can all add up to weight gain and inflammation. “Skipping meals, relying on coffee, being depleted of micronutrients from not eating nutrient-dense meals, overexercising, not getting enough sleep, being woken up in the night on a regular basis, working the night shift, being exposed to xenoestrogens in conventional cleaning or beauty products, pesticides in foods, sugar — [they] can all disrupt these hormones and create a biochemical environment where inflammation and weight gain occur,” Vitti says.

“So it’s important to understand that because the old model of calorie restriction and increased exercise will absolutely not address all of these underlying factors.”

3. Medications

A common culprit behind unexplained weight gain is medication. Whether you’re taking something every day or in the short term, many medications have weight gain as a side effect.

If you’re dealing with weight gain and suspect it could be due to a medication you are taking, talk to your doctor to see if there’s anything you can do to mitigate the side effects like adjust your dose or maybe switch to a different medication. Some examples of medications that can cause weight gain are antidepressants, diabetes medications and blood pressure medications.

4. Aging

It may be a hard truth to accept but people do usually gain some weight as they age. This happens because as you get older your basal metabolic rate, or the amount of calories your body needs, begins to decline — and so does muscle mass.

This means you can eat the same and exercise the same at 50 as you did at 30 years old, but not have the same amount of muscle or be able to maintain the same weight. In order to combat this, it’s important to adjust your food intake and fitness routine accordingly. For example, focusing on adequate protein intake and strength training can be helpful for maintaining healthy muscle mass as you age.

5. Lack of sleep

Missing out on quality sleep is one reason why weight gain can creep up on you. When you’re sleep deprived, you’re probably not that motivated to eat healthy, cook or exercise in the first place. And when you’re not getting enough sleep, you’re more likely to crave unhealthy foods and eat more because you feel so exhausted.

Lack of sleep can throw off your hormones, leading to the issues Vitti mentioned above, and it can mess up your appetite signals, which also explains the tendency to overeat when you’re tired.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.