Last Tuesday was Mardi Gras, traditionally a day of excess just before the start of the church season of Lent. Lent (from the Old English lencten meaning "springtime") is one of two penitential times in the Christian church year, when people are asked to repent for their sins and engage in various forms of self-denial. Many people still talk about "giving something up" for Lent. It seems ironic, then, that the season of Lent should start with a scheduled day of debauchery, "Fat Tuesday" in French, when people are encouraged to eat pancakes or King Cake, drink alcohol, dress in outlandish outfits, and dance in the streets. The event even has theological underpinnings: Medieval clergy offered pre-planned absolution at the start of Lent on the day that is also called "Shrove Tuesday," from the Old English verb shrive (adjective: shrove or shriven) meaning "to offer forgiveness from sins." Lent always made a certain sort of sense to me from a historical perspective: the time right before spring in northern Europe when people were down to their last stores from the prior harvest, and needed to eat sparsely until new food grew again. But why start a season of repentance and denial with a wild party?
If your food stores are running low, it might make sense to whip the last of the fat and the butter into pancakes, in order to put on a few pounds in preparation for the hungry weeks that will follow. But there's an even better psychological reason for this tradition, as demonstrated by psychologist Roy Baumeister: A little bit of excess can actually help people to "store up willpower" for coping with future challenges. Baumeister argued that willpower is actually a function of our blood glucose levels. One piece of evidence for this is that people with low blood sugar are less able to resist advertisements or maintain effort on difficult tasks; a second piece of evidence is that tasks involving effort and self-denial have been shown to rapidly deplete the body's glucose supply; and a third is that giving people a glucose drink seems to restore their ability to exercise self-control. Baumeister's research group has shown all three of these effects. The third, about glucose reinforcing self-control, is the one most directly applicable to Mardi Gras -- at least to the food-related aspects of the holiday.
In Baumeister's study of the "Mardi Gras effect," people were more likely to persevere in a difficult task requiring willpower when they first drank a delicious milkshake. It seemed that a bit of excess had actually strengthened their self-control ability. Another experimental group did just as well, however: Participants who were given a gross-looking green "glop" drink that provided a similar glucose boost. The researchers concluded that the psychological benefits of letting loose weren't nearly as important as the nutritional effects of loading up on glucose. So other types of self-indulgence might not have the same beneficial effects on willpower as a big meal. It's also noteworthy that in Baumeister's study with the milkshakes, people had already completed a prior self-control task that depleted their willpower. The findings therefore may be more about restoring self-control than about facilitating it.
Baumeister's work has been critiqued on statistical grounds, and some other researchers have had difficulty replicating it. A 2016 meta-analysis found mixed results, with the most consistent findings in support of a "glucose rinse" that athletes sometimes use to improve their performance. Again, the effect of glucose may primarily be a restorative one rather than a facilitating one, because the glucose rinse was tested after people were already fatigued. The meta-analysis also found little support for alternative mechanisms by which glucose might improve performance, such as by enhancing mood (which Baumeister also failed to show: the milkshake made people much happier than the green glop, but the resulting improvement in willpower was the same).
On the other hand, there’s strong evidence that at least one other form of letting go can improve subsequent self-control: swearing. In this line of research, people are asked to keep their hand in a bucket of icy water for as long as they can stand it. They are better able to endure when they are encouraged to curse freely during the experience. This is perhaps another example of how one type of self-control can trade off against another. Interestingly, the effect doesn’t work when people shout a novel four-letter word like “kark!” It has to be one of the real, socially impolite ones to have a beneficial effect on willpower.
Baumeister's own summary of the glucose and self-control research is summarized in what he calls the "ego-depletion effect." The basic idea is that many different types of self-control tasks have a similar and cumulative effect in reducing people's ability to engage in further self-control. Low blood sugar may be a marker for that, which could be detected using methods like continuous glucose monitoring. One of the most intriguing aspects of the ego-depletion hypothesis is that people get gradually worn down by self-control tasks, which include things like trying to ignore a television that's on in the room, trying not to pay attention to advertising, or even watching one thing on TV while trying to ignore the scrolling chyron text at the bottom of the screen. As our digital world becomes more immersive and omnipresent, we are increasingly exhausting our limited reserves of self-control. And when we have low blood sugar and less self-control, we are more likely to seek immediate rewards -- perhaps especially sweet or fatty foods that can quickly restore our blood sugar.
For what it's worth, Baumeister doesn't recommend a sugary drink as the best way to restore glucose outside of the lab. A protein bar or piece of beef jerky will provide slower results, but also won't lead to a post-sugar crash that even further reduces our sense of self-control. There's also a good argument in Baumeister's work for planning and limiting the stimuli that tax our self-control. Eat a good breakfast if you have a morning of stressful meetings, avoid mental stress the night before a big test, and don't try to run a marathon on an empty stomach. Recognizing the connection between blood sugar and self-control can help us to manage life's challenges in a healthier way that leaves us less vulnerable to immediate reward-seeking. And a little bit of Mardi Gras feasting can probably help us to keep our Lenten resolutions as well.
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