The article by Baker et al1 in this issue of the Archives is an important piece of evidence supporting the hypothesis that insulin resistance contributes to Alzheimer disease (AD). Baker et al report that insulin resistance in persons with normal cognition and prediabetes or early diabetes without treatment is associated with reductions in cerebral glucose metabolic rate (CMRglu) measured with fludeoxyglucose F 18–positron emission tomography (FDG-PET) in frontal, temporoparietal, and cingulate regions, similar to those observed to predict the development of clinical AD. In addition, persons with prediabetes and type 2 diabetes demonstrated a different pattern of brain activation during a memory encoding task. Based on these results, Baker et al propose that insulin resistance could be an early marker of AD.