UCP1 mRNA does not produce heat

► We discuss molecular and biochemical parameters of recruitment of brown and brite fat. ► UCP1 mRNA levels yield confounding indications of the degree of recruitment. ► Similarly, specific UCP1 protein levels (i.e. per mg protein) are not adequates. ► Only total UCP1 protein per depot/animal correlates with thermogenic capacity. ► Relative UCP1 mRNA increases in brite fat are extremely high but thermogenic capacity comparatively low.