Unexplained weight gain can result from an underlying medical condition, taking certain prescription medicines, and unintentional lifestyle changes. Thyroid disorders and hormonal changes are common causes of unexplained weight gain. A decrease in physical activity and an increase in unhealthy food consumption is an obvious cause, but in turn, this can occur as the result of mood disorders. Medications used to treat diabetes and prevent pregnancy can also lead to sudden weight gain.
Hypothyroidism, which is a condition that causes the thyroid gland to produce an insufficient amount of hormones, is a leading cause of unexplained weight gain. When the thyroid does not produce sufficient levels of hormones, it can result in decreased metabolic levels. Other symptoms of the condition include prematurely gray hair, dry and itchy skin, acne, and heightened reactions to cold temperatures. Unexplained fatigue is an additional symptom of the disorder, as is increased weight gain occurring mostly in the body's mid-section.
Steroids and certain prescription medications can lead to unexplained weight gain. Birth control pills have been known to cause sudden weight gain in certain individuals. The hormonal changes that these pills induce are thought to be the cause. Insulin that is used to treat conditions such as diabetes may also lead to unexplained weight gain. The disease, as well as its treatment, tends to influence the body's metabolic activity.
Changes in metabolic rate due to the aging process or conditions that directly influence hormone levels can cause sudden weight gain. Individuals who decrease their activity levels and do not adjust their diets accordingly may see unwanted pounds added onto their physiques. Increasing consumption of fat and carbohydrates can result in extra weight for aging individuals or those with a slower metabolism.
Mood disorders might also lead to unhealthy eating habits. While these habits might prove to be temporary, individuals may not be fully aware of their behavior. Depression can cause individuals to use food as a coping mechanism in order to make them feel better or emotionally "full." Anxiety is another related mood disorder that may drive individuals to abuse food to alleviate fear and high stress levels.
Natural changes that come with age, such as menopause, can directly affect hormone levels and metabolic activity. Weight gain tends to occur in the mid-section with these types of changes. Conditions not related to aging might also result in sudden weight gain. Polycystic ovary syndrome, which increases the amount of androgens past normal levels, is one of those conditions. Hormonal treatments can usually resolve these issues, but the weight gain may take some time to go away.