Reasons You May Be Gaining Weight:

Tweet Sometimes weight gain is the result of everyday habits such as stuffing our faces with fries and beer, or flaking on our workouts. But it's not always as simple as calories in and calories out.

Endocrine disorders:

Why they lead to weight gain:

Hyperthyroidism:
The most common cause is an under-active thyroid. (a.k.a. hypothyroidism), which can mess with your metabolism. Nearly 26 million Americans have this condition, but less than one-third of them are being properly diagnosed or treated. Thankfully, it can be diagnosed with a simple blood test and controlled with a daily pill.

Polycystic Ovarian Syndrome (PCOS): can also cause weight gain because there is excess glucose floating around in your bloodstream.

Other Symptoms: HYPOTHYROIDISM: Fatigue, weakness, dry skin, dry hair/hair loss, cold intolerance, depression, decreased libido; PCOS: menstrual disturbances, insulin resistance, oily skin, dandruff, infertility, and high cholesterol.

Depression:

Why it leads to weight gain: The brain chemical serotonin regulates mood and appetite. When there is not enough of this chemical, it can cause changes in appetite. Depression can cause isolation and lack of motivation to exercise, which can lead to continued or worsening depression, then more lack of motivation, creating a vicious cycle.

Other Symptoms: Feelings of hopelessness, loss of interest in activities, irritability and restlessness, unexplained aches and pains.

Lack of sleep:

Why it leads to weight gain:

Not getting enough sleep can disrupt normal hormone cycles and increase your appetite. When people get insufficient sleep, they develop insulin resistance which leads to intense sugar cravings. At the same time, two major hormones controlling appetite, ghrelin and leptin, also change with even brief sleep deprivation in ways that appear to lead to weight gain.

Other Symptoms: You toss and turn all night long and are exhausted 24/7, inability to focus during the day.

Medications:

Why they lead to weight gain: A few of the most likely culprits are diabetes medications, oral contraceptives (generally, about 3 to 5 pounds; though, it's important to note that some people lose weight on BCPs), Depo-Provera shots (commonly 5 to 10 pounds a year), and anti-depressant meds (which may be due more to the depression than the medication).

Other Symptoms: Depends on the medication. Talk to your doctor about potential side effects anytime you're prescribed new meds.

Stress:

Why it leads to weight gain: Studies have linked increase levels of cortisol, a hormone that's released in response to stress. Cortisol levels increasing cause excess belly fat in women. The adrenal gland is the body's stress handler. Excess stress can initially cause elevated followed by inadequate cortisol levels, both of which can result in weight gain. To treat this problem, start by switching up your attitude: Whenever you notice that you're getting anxious or worried ask yourself the simple question, 'Am I in imminent danger?' The answer is almost always no, and you'll find that your adrenal glands relax after you realize this.

Other Symptoms: Feeling angry or agitated, feeling depressed, feeling frozen under pressure.