Obesity

Certain medical conditions may also lead to weight gain. These include:
polycystic ovary syndrome (PCOS): a condition that causes an imbalance of female reproductive hormones

Cushing’s syndrome: a condition caused by having an excessive amount of the hormone cortisol in your system
hypothyroidism (underactive thyroid): a condition in which the thyroid gland does not produce enough of certain important hormones

Common specific causes of obesity include:
eating a poor diet of foods high in fats and calories
having a sedentary (inactive) lifestyle
not sleeping enough, which can lead to hormonal changes that make you feel more hungry and crave
certain high-calorie foods
genetics, which can affect how your body processes food into energy and how fat is stored
growing older, which can lead to less muscle mass and a slower metabolic rate, making it easier to gain weight
pregnancy (weight gained during pregnancy can be difficult to lose and may eventually lead to obesity)