APOE and Alzheimer disease: Considering these findings relative to AD, we propose a tentative model wherein (i) APOE2 is associated with an increase in the relative abundance of microbiome bacteria like Ruminococcaceae, relative to APOE3 and APOE4, (ii) this shift in bacterial profile increases the efficiency of resistant starch metabolism to SCFAs and (iii) this increase in SCFAs promotes microglial function (64) to reduce AD risk, as suggested by robust genetic evidence (65–72), [reviewed in (73, 74)].