The well-balanced secretion between insulin and growth hormone (GH) is essential in regulating substrate metabolism, energy metabolism and body composition. Hyperinsulinemia and reduced GH secretion are often observed in obese individuals, leading to reduced energy expenditure and further fat accumulation. Although suppression of hyperinsulinemia has been proposed as a treatment for obesity, changes in GH secretion following the suppression of hyperinsulinemia in obesity are unknown. This leaves unexplained observations, such as unchanged lean mass following insulin reduction. Besides, the energy metabolism following the suppression of hyperinsulinemia in obesity has not been thoroughly investigated. In this study, high-fat diet-induced obese (DIO) and normal chow-fed lean mice on a C57BL/6J background were treated for 7 weeks with diazoxide (1250 mg/kg in food), a KATP channel opener that suppressed insulin secretion. Diazoxide treatment for 10 days was sufficient to increase pulsatile GH secretion in DIO mice prior to any significant body weight change. The restored insulin-GH balance in DIO mice was followed by improvement in substrate and energy metabolism in a prolonged treatment period (4-6 weeks), including reduced fat mass, increased lipid oxidation and energy expenditure, as well as improved insulin sensitivity and metabolic flexibility. These metabolic benefits occurred along with the changes in the expression level of genes regulated by the insulin-GH balance. When applying diazoxide to normal chow-fed non-hyperinsulinemic lean mice, none of the above metabolic effects was observed, suggesting that the metabolic changes following diazoxide treatment were mediated through the suppression of hyperinsulinemia. Therefore, suppression of hyperinsulinemia by diazoxide restores insulin-GH balance followed by improvement in substrate and energy metabolism in DIO mice.