SPEG and obesity due to melanocortin 4 receptor deficiency: To the best of our knowledge, this study is the first to report that the SPEG protein in the hippocampus, a peripheral blood biomarker in patients with obesity with concomitant T2DM and neurodegenerative diseases, can bind to acetamidobenzoic acid, a high-fiber-diet-related metabolite, and plays an important role in the development of T2DM and neurodegenerative diseases in patients with obesity.