A 35-year-old woman presents to the endocrinology clinic with concerns about progressive weight gain. Despite adhering to a healthy diet and maintaining a regular exercise routine, she reports a gradual increase in weight over several years. Her medical history is unremarkable, though she notes a family history of obesity. She also describes a previously regular menstrual cycle that has become irregular over the past year; during these episodes of amenorrhea, both serum and urine β-hCG tests were negative. On examination, her body mass index is 32 kg/m², with evidence of central adiposity. Laboratory studies reveal normal fasting glucose and thyroid function but elevated fasting insulin levels. Which of the following conditions most likely accounts for this patient’s obesity?