From Thinking, Fast and Slow (Daniel Kahneman):
A disturbing demonstration of depletion effects in judgment was recently reported in the Proceedings of the National Academy of Sciences. The unwitting participants in the study were eight parole judges in Israel. They spend entire days reviewing applications for parole. The cases are presented in random order, and the judges spend little time on each one, an average of 6 minutes. (The default decision is denial of parole; only 35% of requests are approved. The exact time of each decision is recorded, and the times of the judges’ three food breaks – morning break, lunch, and afternoon break – during the day are recorded as well.) The authors of the study plotted the proportion of approved requests against the time since the last food break. The proportion spikes after each meal, when about 65% of request are granted. During the two hours or so until the judges’ next feeding, the approval rate drops steadily, to about zero just before the meal. As you might expect, this is an unwelcome result and the authors carefully checked many alternative explanations. The best possible account of the data provides bad news: tired and hungry judges tend to fall back on the easier default position of denying requests for parole. Both fatigue and hunger probably play a role.
Disturbing, no? Sheesh. I can think of a gazillion other situations where this effect could lead to horrible outcomes.
Kahneman adds, “the nervous system consumes more glucose than most other parts of the body, and effortful mental activity appears to be especially expensive in the currency of glucose.” Basically, when we engage in tasks that require significant concentration and self-control, we need energy to do it well. If we don’t have that energy, we either fall back to a less taxing mode of operation (e.g. thinking less, saying “no” to acquittals, etc.) or our cognitive performance deteriorates. Multiple studies have confirmed this effect (though, frankly, it should be common sense). I guess all those commercials about making sure we eat breakfast before school were right.
What’s disturbing about this is that most folks, groups or companies do not account for this effect in their daily lives or day-to-day operation. Yes, we know we’re tired and hungry when we don’t eat, and we get cranky and sleepy. We don’t want to do our work or we go at it half-steam. Performance drops. But I don’t think it crosses our minds too often that our judgment is actually “impaired,” and that in this state, we can make significant mistakes in life-altering decisions (for ourselves and others).
Ultimately, most of the time, glucose-depletion probably won’t lead to major catastrophes in your life. For me, it can cause me to be short with people, including my wife. (She’s learned to feed me when I’m cranky, which usually solves the problem.) But sometimes, the consequences can be significant. So I’d advise against making important decisions in a glucose-depleted state. And I hope companies and structures (like parole boards!) are somehow incorporating these findings in their planning and operations. I’d hate to see a reformed person get turned down because a judge didn’t eat. (Yes, the recidivism rate is high, but that’s all the more reason the judge needs to be mentally alert so she can factor that variable in.)
What’s the moral of the story. Well, there’s a few (and probably more, but I’m mentally depleted at the moment):
- Students: Eat breakfast & drink something sugary before an exam. (Artificial sweetener doesn’t work.) Don’t eat anything too heavy because that might have the opposite effect.
- Be aware of your mental and bodily state (i.e. before doing something that’s mentally taxing, did you replenish yourself?). This is easier said than done.
- Eat healthy snacks at regular intervals, especially when you feel your performance dropping.
- Christians: Not everything is “spiritual.” When the prophet Elijah was running away from Jezebel’s cronies, he got to a point where he was so depressed that he asked God to kill him. You know what God said to him? Pray harder? Repent? No. He said, “Get up and eat.” If you’re in a bad mood or depressed or can’t perform well, don’t jump to thinking it’s a demon or you’re in a sinful mode. Maybe you just need to eat?!
Of course, there is a caveat to all of this. Sometimes overthinking can lead to errors in judgment (e.g. making a football pass during a game, etc.), but that’s a topic for another day. For now, it’s a safe bet that being aware of our mental & bodily state, eating well & eating regular light snacks can help give us the resources to fuel our cognitive apparatus and improve our performance. That is, hopefully. For example, if you don’t study and you just have some fruit before an exam, you might be more alert and have the necessary glucose to power your brain, but you’ll still stink up the test. ;p