No, Sugar Doesn't Boost Willpower!

The idea that consuming glucose boosts willpower is a myth. I’ve already explained this in my book Willpower Condensed. This summer, two new meta-studies were published on the topic, with the result: Sugar is not willpower fuel (or, more scientifically accurate, we don’t have enough evidence to claim a significant effect).

The Glucose Hypothesis

The glucose hypothesis of self-control states that sugar is the physiological substrate of willpower, more precisely:

When you use willpower, your blood glucose levels drop.
When your blood glucose levels are low, your willpower performance is impaired.
When you elevate your blood glucose levels by consuming sugar, you have more willpower.

Theoretical Problems

The glucose hypothesis is biologically implausible because changes in peripheral blood glucose levels don’t necessarily reflect how much glucose is used by the brain. Also, the energy needed for any one particular task is negligible, no matter how much willpower you need to perform it.

Furthermore, vigorous physical exercise consumes plenty of energy and depletes blood glucose levels; ironically, though, exercise improves, rather than impairs, self-control. This makes the glucose hypothesis already dubious from a theoretical perspective.

Meta-Analyses

Two recent studies tested the glucose hypothesis on a meta-level:

Junhua Dang (2016) from Lund University, Sweden, included 11 experimental studies and calculated Hedges’ g; the standardized group mean differences were insignificant.
Miguel Vadillo et al. (2016) from King’s College London, England, included 19 experimental studies and performed a p-curve analysis, which critically examines the distribution of significant p values (this video by Veritasium explains why such an analysis is important); the difference between the distribution of p values and the expected distribution if the effect were zero was insignificant (in other words, the distribution suggests that the results of the studies supporting the glucose hypothesis are false positives).

In addition to multiple replication failures, even studies that allegedly show that sugar boosts willpower have little to no evidential value. It remains unclear, however, whether these studies had significant results due to publication bias, p-hacking, or both.

It’s All In Your Head

Nonetheless, there is one glucose-related effect that turned out to be significant: the rinsing effect—when you rinse your mouth with a glucose solution, your willpower increases, even if you don’t swallow it (= no metabolic effect, no elevated blood glucose levels).

This happens because oral receptors sensitive to glucose signal activation to certain brain regions responsible for reward and motivation, specifically the anterior cingulate cortex, which has been associated with willpower. Of course, I’ve covered this effect in my book Willpower Condensed.

In Summary

Don’t think that you can boost your willpower by eating or drinking sugar. If you want to trick your brain into self-control mode, gargle some Coca Cola, but don’t drink that shit. Sugar will only weaken you in the long term.

Resources

Dang, J. (2016), Testing the role of glucose in self-control: A meta-analysis, Appetite, Epub ahead of print, doi: 10.1016/j.appet.2016.07.021.

Vadillo, M. A., Gold, N., Osman, M. (2016). The Bitter Truth About Sugar and Willpower: The Limited Evidential Value of the Glucose Model of Ego Depletion, Psychological Science, Epub ahead of print, doi: 10.1177/0956797616654911.