Abstract: Provided are methods for assessing samples to determine or to aid in determining Insulin Resistance and/or malfunctioning adipocytes. The methods involve analysis of non-esterified fatty acids (NEFAs) trafficking by determining kinetic parameters that include the fractional rate of NEFA appearance (Ra), the rate of NEFA disappearance (kNEFA), threshold for glucose-induced suppression (tG), and IC50 for glucose inhibition of NEFA production (glCso). Determining Ra for stearate that is similar to a control value, and/or a kNEFA for stearate that is higher than a control, indicates that the individual from whom the sample was taken has IR and/or adipocyte dysfunction. The method can include analysis of trafficking patterns for one or more of myristic, palmitic, palmitoleic, oleic, and linoleic acids, in addition to stearate. A determination of IR and/or adipocyte dysfunction can indicate that the individual is a candidate for treatment with an agonist of a peroxisome proliferator-activated receptor.