A very low-protein diet caused weight decline and improved glucose tolerance partially through hypothalamic mTOR signalling.226 Then, KD is found to improve cognition in mild cognitive impairment,227 while methionine restriction increases FGF21 expression in serum, liver, and brain to alleviate age-associated cognitive decline.228 Interestingly, the supplement with non-essential amino acids results in appetitive suppression through direct activation of hypothalamic orexin/hypocretin neurons.229. This evidence concerns the gene HCRT and Mental deterioration.