INS and Impaired glucose tolerance: A study from the Insulin Resistance Atherosclerosis Study (IRAS) reported that decaffeinated coffee, but not caffeinated coffee, was favorably related to measures of BCF, measured by the intact and split proinsulin to C-peptide ratios, and a cross-sectional study in Sweden showed that there was an association between high coffee consumption and beta cell function in those with diabetes and impaired glucose tolerance, but not in subjects with normal glucose tolerance [4,16].