Powdered edible locust enhances nitrogen excretion and presents a low-energy value in growing rats

Edible insects are increasingly recommended as novel sustainable protein sources, but the nutritional properties of edible insects have not been well studied. We investigated whether locust powder can be used as a nutritionally functional food resource with a low energy value using a rat model. Twenty-five male Wistar rats (4-week-old) were fed a basal diet (12 g daily) to which a fixed amount of locust powder (0, 0.5, 1.0, or 2.0 g) was added for 20 days (L0, L0.5, L1.0, and L2.0 groups, respectively). In the sucrose standard group, rats received 12 g of the basal diet daily and 2.0 g of sucrose daily for 20 days (S2.0 group). Body-weight gain and the nutritional composition of the carcasses and feces were determined to estimate the available energy value of locust powder. The L0.5 group had the lowest carcass fat content and energy accumulation, but these values were increased by locust powder in a dose-dependent manner. The net energy value of locust powder was estimated to be 2.78 kcal/g, which was expected to be lower than the calculated theoretical value (4.25 kcal/g) and that of sucrose (3.94 kcal/g). Fecal nitrogen excretion was increased by dietary locust powder in a dose-dependent manner (correlation coefficient, R = 0.98), and the carcass nitrogen percentage was not changed, regardless of the dietary content of the locust powder, indicating an increased excretion of proteins or other non-protein nitrogen compounds derived from the locust powder. These findings suggest that locust powder can be used as a novel food material with a low energy value for humans.