Respiratory exchange ratios (RER, CO_{2 production divided by oxygen consumption) range from 0.7 (fats) to 1 (carbohydrates) depending on fuels used for catabolism. Elevation of RER above 1 has been previously observed, and this has been proposed to be due to either synthesis of lipid from carbohydrate or catabolism of carbohydrate via the pentose phosphate pathway to augment glutathione (antioxidant) production. We measured RER and lipid synthesis in late-instar South American locusts (Schistocerca cancellata) fed on artificial diets varying in protein:carbohydrate (p:c) ratio for 3-5 days. In both outbreaking field populations in Paraguay and the Arizona lab colony, when removed directly from food, RER values increased as the p:c content of the diet decreased, reaching 1.2 on the lowest p:c diet. Lipid synthesis also increased linearly as p:c decreased, and theoretical calculations suggest that lipid synthesis can account for the observed elevations in RER. Surprisingly, when RER was measured for nymphs while feeding, values were always 1. Our results strongly support the hypothesis that in locusts, RER above 1 can result from lipid synthesis from carbohydrates occurring after cessation of feeding on high carbohydrate diets. This research was supported by NSF IOS-1826848 and BARD FI-575-18.}