What Enables Self-Control? A Test of Glucose, Fructose, and Vagus Nerve Activation as Possible Factors

This study replicated the study by Miller, Bourrasseau, and Blampain (2013) on the effects of fructose and glucose on self-control. It also investigated these authors' suggestion that self-control may be under the influence of the vagus nerve, which can be activated by forceful exhalation in the Valsalva manoeuvre. The participants (N = 101) were assigned to one of five conditions: three groups that received a solution of either glucose, fructose, or a placebo sweetener (solution condition); and two groups that underwent the Valsalva manoeuvre (VM and VM-control). Participants in the solution condition groups ingested one of the three sweeteners, whereas those in the VM and VM-control conditions were required to blow or not blow into a manometer for 15 seconds, respectively. The number of anagrams that participants subsequently completed was used to assess their level of self-control. In contrast to the results obtained by Miller et al. (2013), it was found that fructose, glucose, and VM did not increase the participants' levels of self-control compared to control subjects. These negative results concur with several recent studies which document the difficulty of replicating published findings in psychology.