A Snickers bar can save you money. Not just a little money either. Used correctly, it could potentially spare you thousands of dollars.

That’s the gist of new research on a phenomenon called “decision fatigue”. Decision fatigue is what happens to people when they’ve made too many choices. As your brain gets tired, you become worse at making decisions.

As the New York Times puts it:

Decision fatigue helps explain why ordinarily sensible people get angry at colleagues and families, splurge on clothes, buy junk food at the supermarket and can’t resist the dealer’s offer to rustproof their new car. No matter how rational and high-minded you try to be, you can’t make decision after decision without paying a biological price.

It’s different from ordinary physical fatigue — you’re not consciously aware of being tired — but you’re low on mental energy. The more choices you make throughout the day, the harder each one becomes for your brain, and eventually it looks for shortcuts, usually in either of two very different ways.

One shortcut is to become reckless: to act impulsively instead of expending the energy to first think through the consequences. (Sure, tweet that photo! What could go wrong?) The other shortcut is the ultimate energy saver: do nothing. Instead of agonizing over decisions, avoid any choice. Ducking a decision often creates bigger problems in the long run, but for the moment, it eases the mental strain.

If you’ve ever paid attention to your shopping habits, you’re probably familiar with decision fatigue, even if you didn’t know it had a name. It’s the reason my family has a hard and fast rule to never go to the grocery store hungry.

I have to believe it’s decision fatigue that fuels shopping momentum, that pesky tendency to keep spending money once you’ve started. It’s certainly decision fatigue that fuels impulse buys in the checkout aisle and causes people to wave their hands over the details of wedding planning.

Limited willpower
Researchers are finding that willpower really is an expendable resource. Some people have more or less of it. It’s possible to strengthen our ability to resist impulsiveness and bad choices. But no one can make the same quality of decisions all the time. We wear ourselves down by using our willpower, and become prone to poor choices until we replenish our strength.

This is a phenomenon that affects the poor more than the affluent. Because they have fewer resources, those who are strapped for cash must more constantly be weighing the pros and cons of even very small decisions. It might be trivial for one person to spend ten dollars for a lunch out with coworkers. For another, that ten dollars could make or break his week’s grocery budget. The poorer person will exhaust his willpower faster because every spending decision comes with a high energy cost due to how stressful it is.

Decision fatigue is especially hard on the poor, but it’s not just a poor person’s problem. Rich or poor, smart or dumb, young or old, decision fatigue will catch up with you if you tax your brain heavily enough.

A sweet solution
Now about that Snickers bar I mentioned in the opening. Decision fatigue is a biological process that affects our ability to think rationally and make good decisions. And it has a surprising cure: a quick shot of glucose.

So if you’ve exhausted your reserves of willpower negotiating with your car salesman or real estate agent or wedding planner, and you’re being called on to make the final decisions, it’s a great time to indulge in a candy bar. The sugary treat will flood your brain with glucose in minutes, enabling you to make decisions with a fresh base of willpower to work from.

Of course, an even better strategy is to eat well before you’re called on to make a series of complex decisions. Protein rich foods will give you longer-lasting boosts to the glucose levels in your brain. But, as the NYT article warns, decision fatigue doesn’t have a clear warning sign like hunger or physical exhaustion. You can’t always tells when your ability to make good choices is deteriorating.

Given that, I think I’ll keep a candy bar in my pocket next time I have to make a complicated, major purchase like buying a car. It can’t hurt, and it might help.

How to make smart decisions
Other good strategies for managing decision fatigue include two factors: learning to avoid it, and knowing when it might set in so you can avoid making major decisions in a depleted state. The research team that discovered decision fatigue says the best decision makers are those who pace their decision-making, and only make important decisions when they’re rested and fed. They suggest:

• sticking to decision-making only when sober
• avoiding scheduling multiple meetings back to back
• make important decisions early in the day
• if you must make a choice late in the day, don’t do it on an empty stomach

This is all simple good advice. Probably you learned most of it from your mother. If you didn’t, you figured it out through trial and error in young adulthood. What makes this so compelling is the science behind it. You’re not wrong when you feel like your brain is turning to mush after a long day and you just can’t think straight. Well, you’re wrong about the mush part, but there really is a biological change that stops you from thinking as clearly as you do when you start your day.

While common sense shows us many good strategies to avoid decision fatigue, I really would not have guessed that a milkshake or candy bar could act as a kind of band-aid to deal with it once it sets in. As a mom, I know how important it is to carry snacks for little ones to stave off meltdowns when they start to get hungry. Now I’ll be carrying some for myself as well.

Have you encountered decision fatigue in your life? What strategies do you use to combat it?