Self-control is a finite resource, goes the ego deple­tion the­ory, and through var­i­ous means can be “used-up”. What, exactly, depletes and builds this resource isn’t fully known but a num­ber of stud­ies have shown some intrigu­ing cor­re­la­tions with blood glu­cose level (explain­ing, pos­si­bly, the cookie self-control study).

The abstract of a study by Roy Baumeis­ter sum­marises the find­ings nicely, show­ing clearly the pos­si­ble impor­tance of keep­ing a mod­er­ate blood sugar in order to main­tain self-control:

Past research indi­cates that self-control relies on some sort of lim­ited energy source. This review sug­gests that blood glu­cose is one impor­tant part of the energy source of self-control. Acts of self-control deplete rel­a­tively large amounts of glu­cose. Self-control fail­ures are more likely when glu­cose is low or can­not be mobi­lized effec­tively to the brain (i.e., when insulin is low or insen­si­tive). Restor­ing glu­cose to a suf­fi­cient level typ­i­cally improves self-control. Numer­ous self-control behav­iors fit this pat­tern, includ­ing con­trol­ling atten­tion, reg­u­lat­ing emo­tions, quit­ting smok­ing, cop­ing with stress, resist­ing impul­siv­ity, and refrain­ing from crim­i­nal and aggres­sive behav­ior. Alco­hol reduces glu­cose through­out the brain and body and like­wise impairs many forms of self-control. Fur­ther­more, self-control fail­ure is most likely dur­ing times of the day when glu­cose is used least effec­tively. Self-control thus appears highly sus­cep­ti­ble to glu­cose. Self-control ben­e­fits numer­ous social and inter­per­sonal processes. Glu­cose might there­fore be related to a broad range of social behavior.

via Hacker News