Eugenol, like other antidepressants, increases expression of brain-derived neurotrophic factor (BDNF) gene in the hippocampus, which is necessary for an antidepressant to exhibit its activity.
More research is being conducted on this subject, but what seems clear in any case is that a reduced level of BDNF is bad news for our brains, and chronic sugar consumption is one of the worst inhibitory culprits.
In other words, chronically eating added sugar reduces BDNF, and then the lowered levels of the brain chemical begin contributing to insulin resistance, which leads to type 2 diabetes and metabolic syndrome, which eventually leads to a host of other health problems.