A 38-year-old woman from Chennai presents with a 3-month history of progressive weight loss (8 kg), heat intolerance, and palpitations. On examination, she is tremulous, has a resting heart rate of 112/min, and warm, moist skin. Thyroid function tests confirm TSH 0.02 mIU/L (normal 0.4–4.0) and free T4 8.8 ng/dL (normal 0.8–1.8). She is diagnosed with Graves' disease. The patient asks why she is losing weight despite eating more than usual. Which of the following best explains the mechanism of weight loss in hyperthyroidism?