1. Introduction
cardiometabolic diseases, cardiometabolic disease, autonomic dysfunction
DISEASE, HYPERGLYCEMIA, AUTONOMIC DYSFUNCTION, AUTONOMIC DYSFUNCTION, HEART
Heart rate variability (HRV) provides a simple method to evaluate autonomic function in health and disease. A reduction in HRV may indicate autonomic dysfunction and is strongly associated with aspects of cardiometabolic disease, including hyperglycemia. Reduced nitric oxide (NO) bioavailability is also implicated in the development of cardiometabolic disease and autonomic dysfunction. Watermelons are natural sources of L-arginine and L-citrulline, substrates used for NO synthesis. Watermelon consumption can improve NO bioavailability. We conducted a randomized, double-blind, placebo-controlled crossover trial to test the effects of 2 weeks of daily watermelon juice (WMJ) supplementation on HRV in response to an oral glucose challenge (OGC) in healthy young adults. We also performed indirect calorimetry to assess if our intervention altered the metabolic response to the OGC. WMJ supplementation preserved high-frequency power (HF) (treatment effect, Autonomic dysfunction is an emerging mechanism in the development of cardiometabolic disease [Deficits in energy expenditure and substrate utilization are also aspects of autonomic dysfunction that characterize cardiometabolic diseases. During meal feeding or insulin stimulation, hormonal and sympathovagal coordination regulates blood flow and metabolic flux. In healthy men, postprandial energy expenditure correlates with sympathetic nervous system activity [An oral glucose challenge (OGC) has been shown to reduce HRV in diverse patient populations [The loss of NO bioavailability and reduction in HRV during an OGC suggests that these phenomena may be causally linked. To date, no studies have explored the protective effects of NO donor therapy on hyperglycemia-induced autonomic dysfunction and metabolic function. In a randomized, double-blind, placebo-controlled crossover trial, we studied the effects of two weeks of WMJ supplementation on HRV and metabolic control during an oral glucose challenge (OGC). We hypothesized that increased NO bioavailability via WMJ supplementation would attenuate the decline in HRV during brief, transient hyperglycemia. We also sought to evaluate our intervention’s impact on metabolic parameters (energy expenditure and substrate oxidation) using indirect calorimetry. 