Abstract: A method of diagnosing and treating insulin resistance at the end of a first phase insulin response to glucose in a mammalian subject is disclosed. The method includes administering an amount of glucose to the mammalian subject capable of producing a first phase insulin response to glucose. At the end of the first phase insulin response to glucose, a serum sample is obtained from the mammalian subject, from which the levels of at least one biomarker for insulin resistance may be measured, from a group including insulin, proinsulin, C-peptide, glucose, and hemoglobin A1c. An analysis of the levels of the biomarkers in the serum samples may be performed to determine if the mammalian subject is insulin dependent. If the mammalian subject is determined to have insulin resistance, treatments for insulin resistance may be prescribed. Prescribed treatments include weight loss, dietary modification, exercise, or drug therapy.