The inventors have determined that increasing the expression level or activity of FKBP-L polypeptide in a subject, which can be provided by expression of nucleic acids encoding FKBP-L or by providing FKBP-L polypeptides to a subject is advantageous for use in the treatment of obesity and obesity-related disorders. In particular increased expression or activity of FKBP-L polypeptide in a subject may be used to treat excessive weight gain (which can be characterised as obesity), glucose intolerance, diabetes and metabolic syndrome, which are closely linked to obesity and insulin resistance. FKBP-L can also be used as a biomarker for obesity and obesity-related disorders.