BDNF and type 2 diabetes mellitus: Previous studies highlighted various mechanisms to explain the depressogenic effects of elevated sugar consumption, including (1) the increased level of circulating inflammatory markers through insulin secretion, and (2) the subsequent decrease of BDNF; through (3) somatic conditions comorbid with depression, including obesity, type II diabetes, and cardiovascular disease; (4) alterations in the gut microbiome and gut–brain circuits; and (5) increased oxidative stress [13,33,34,35].