What is the most likely cause of hypertension in the 7-year-old boy with symptoms of sweating and a racing heart?

The presence of sweating and a racing heart in the 7-year-old boy strongly suggests a state of heightened adrenergic activity, which is commonly associated with catecholamine excess. This condition can arise from various causes, such as a pheochromocytoma, which is a tumor that secretes catecholamines, leading to symptoms like hypertension, palpitations, and diaphoresis.

Catecholamines, which include epinephrine and norepinephrine, are hormones that prepare the body for "fight or flight" responses, resulting in increased heart rate and blood pressure. Given the combination of hypertension along with sympathetic nervous system symptoms—like sweating and a rapid heartbeat—catecholamine excess emerges as the most plausible explanation for his symptoms.

In contrast, dehydration typically leads to hypotension rather than hypertension, and the other options such as dietary factors and metabolic syndrome would not directly present with such acute symptoms of sweating and a racing heart in an otherwise healthy 7-year-old. Therefore, catecholamine excess is the most coherent explanation for the observed symptoms in this clinical scenario.