Lipids and carbohydrates have long been measured in organisms with various techniques. The microseparation and calorimetric method for quantifying lipids with a vanillin reagent, and glycogen and sugars with an anthrone reagent in mosquitoes described by Van Handel have been adapted widely for many insect species. Given the common use of this technique and variety of applications, a review is warranted. First, the procedure and adaptations are described, followed by other procedures available for quantifying energetic reserves. Next, practical logistics for running assays are discussed for new users. Previously, these assays have been reviewed for studying the sugar feeding behavior of biting flies and parasitoids. This review will survey a wider variety of applications from 85 papers with an emphasis on publications since 2004. For example, nutrient assays have been applied to establish the baseline energetic reserves of insects under various conditions, evaluating habitat manipulation programs, to better understand maternal allocation, overwintering and mating behavior, and flight energetics.