Apparatus and methods for assessing metabolic substrate utilization are described. In one embodiment, a processor-readable medium includes code to receive data indicative of a plasma glucose concentration, a plasma free fatty acid concentration, and a respiratory quotient of a subject. The processor-readable medium also includes code to calculate, based on the data, respective values of a set of metabolic parameters. The set of metabolic parameters includes a first metabolic parameter and a second metabolic parameter. The value of the first metabolic parameter is indicative of whether the subject has a predisposition towards oxidation of a first type of metabolic substrate or a second type of metabolic substrate, and the value of the second metabolic parameter is indicative of the subject's responsiveness to a change in availability of the first type of metabolic substrate or the second type of metabolic substrate.