Weight gain refers to an increase in body weight. This can involve an increase in muscle mass, fat deposits, excess fluids such as water, or other factors. Weight gain can be a symptom of a serious medical condition, or it can be due to lifestyle factors.

Here are a few common causes of weight gain:

1. Overeating and Lack of Physical Activity: Consuming more calories than your body needs for energy, particularly when those calories come from high-fat or high-sugar foods, can lead to weight gain. Likewise, living a sedentary lifestyle, or not getting enough physical activity, can also lead to weight gain.
2. Hormonal Changes: Certain hormonal changes can cause weight gain. For example, hypothyroidism, or having an underactive thyroid, can slow down metabolism and cause weight gain. Additionally, hormonal changes during menopause can also lead to weight gain.
3. Medications: Certain medications can contribute to weight gain, including some forms of hormonal birth control, steroids, antidepressants, and medications used to treat bipolar disorder and schizophrenia.
4. Stress and Emotional Factors: Some people eat more when they’re stressed, anxious, or depressed, which can lead to weight gain.
5. Sleep Deprivation: Lack of sleep may disrupt the balance of key hormones that control appetite, so sleep deprivation could be a factor in weight gain.
6. Medical Conditions: Some diseases and conditions can lead to weight gain, such as polycystic ovary syndrome (PCOS), Cushing’s syndrome, and depression.

Weight gain can have significant health implications if it results in overweight or obesity. Such conditions are associated with a higher risk for a number of health conditions, including heart disease, diabetes, and some forms of cancer. Therefore, it’s important to maintain a healthy weight. If you’re experiencing unexplained weight gain, it’s important to consult with a healthcare professional to understand potential underlying causes and appropriate interventions.