Here is a very insightful article about decision fatigue. Too many choices wear out your brain. Difficulties in compromising—like shopping among many possibilities, when you have limited money to buy your preferred item—also make you punchy. So guess what happens next? Your brain craves sugar, the real thing, glucose…no artificial sweetener. The result is additional calories. Who’d have thought it? And there are many other consequences as well, unrelated to diet, but affecting judicial sentences, your lack of willpower to keep exercising or reject other temptations (your neighbor’s wife?), your ability to keep on working. Check it out after looking over some of these excerpts.

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…

These experiments demonstrated that there is a finite store of mental energy for exerting self-control. When people fended off the temptation to scarf down M&M’s or freshly baked chocolate-chip cookies, they were then less able to resist other temptations. Willpower really was a form of mental energy that could be exhausted. The experiments confirmed the 19th-century notion of willpower being like a muscle that was fatigued with use, a force that could be conserved by avoiding temptation. When you shop till you drop, your willpower drops, too.

The brain, like the rest of the body, derives energy from glucose, the simple sugar manufactured from all kinds of foods. The sugar restored willpower, but the artificial sweetener had no effect. The restored willpower improved people’s self-control as well as the quality of their decisions:

Your brain does not stop working when glucose is low. It stops doing some things and starts doing others. It responds more strongly to immediate rewards and pays less attention to long-term prospects.

The discoveries about glucose help explain why dieting is a uniquely difficult test of self-control—and why even people with phenomenally strong willpower in the rest of their lives can have such a hard time losing weight. They start out the day with virtuous intentions, resisting croissants at breakfast and dessert at lunch, but each act of resistance further lowers their willpower. As their willpower weakens late in the day, they need to replenish it. But to resupply that energy, they need to give the body glucose. They’re trapped in a nutritional catch-22:

1. In order not to eat, a dieter needs willpower.

2. In order to have willpower, a dieter needs to eat.

As the body uses up glucose, it looks for a quick way to replenish the fuel, leading to a craving for sugar. After performing a lab task requiring self-control, people tend to eat more candy but not other kinds of snacks, like salty, fatty potato chips. The mere expectation of having to exert self-control makes people hunger for sweets. A similar effect helps explain why many women yearn for chocolate and other sugary treats just before menstruation: their bodies are seeking a quick replacement as glucose levels fluctuate. A sugar-filled snack or drink will provide a quick improvement in self-control (that’s why it’s convenient to use in experiments), but it’s just a temporary solution. The problem is that what we identify as sugar doesn’t help as much over the course of the day as the steadier supply of glucose we would get from eating proteins and other more nutritious foods.

When there were fewer decisions, there was less decision fatigue. Today we feel overwhelmed because there are so many choices. Your body may have dutifully reported to work on time, but your mind can escape at any instant. A typical computer user looks at more than three dozen Web sites a day and gets fatigued by the continual decision making.

Virtually no one has a gut-level sense of just how tiring it is to decide. Big decisions, small decisions, they all add up. Choosing what to have for breakfast, where to go on vacation, whom to hire, how much to spend—these all deplete willpower, and there’s no telltale symptom of when that willpower is low. It’s not like getting winded or hitting the wall during a marathon. Ego depletion manifests itself not as one feeling but rather as a propensity to experience everything more intensely. When the brain’s regulatory powers weaken, frustrations seem more irritating than usual. Impulses to eat, drink, spend and say stupid things feel more powerful (and alcohol causes self-control to decline further).

People with the best self-control are the ones who structure their lives so as to conserve willpower. They don’t schedule endless back-to-back meetings. They avoid temptations like all-you-can-eat buffets, and they establish habits that eliminate the mental effort of making choices. Instead of deciding every morning whether or not to force themselves to exercise, they set up regular appointments to work out with a friend.

“Even the wisest people won’t make good choices when they’re not rested and their glucose is low,” Baumeister points out. if a decision must be made late in the day, they know not to do it on an empty stomach. “The best decision makers,” Baumeister says, “are the ones who know when not to trust themselves.”

To compromise is a complex human ability and therefore one of the first to decline when willpower is depleted. Decision fatigue is a major—and hitherto ignored—factor in trapping people in poverty. Because their financial situation forces them to make so many trade-offs, they have less willpower to devote to school, work and other activities that might get them into the middle class. It’s hard to know exactly how important this factor is, but there’s no doubt that willpower is a special problem for poor people. Study after study has shown that low self-control correlates with low income as well as with a host of other problems, including poor achievement in school, divorce, crime, alcoholism and poor health.

In one study, he found that when the poor and the rich go shopping, the poor are much more likely to eat during the shopping trip. This might seem like confirmation of their weak character—after all, they could presumably save money and improve their nutrition by eating meals at home instead of buying ready-to-eat snacks like Cinnabons, which contribute to the higher rate of obesity among the poor. But if a trip to the supermarket induces more decision fatigue in the poor than in the rich—because each purchase requires more mental trade-offs—by the time they reach the cash register, they’ll have less willpower left to resist the Mars bars and Skittles. Not for nothing are these items called impulse purchases.

And this isn’t the only reason that sweet snacks are featured prominently at the cash register, just when shoppers are depleted after all their decisions in the aisles. With their willpower reduced, they’re more likely to yield to any kind of temptation, but they’re especially vulnerable to candy and soda and anything else offering a quick hit of sugar. While supermarkets figured this out a long time ago, only recently did researchers discover why.

Desire turned out to be the norm, not the exception. Half the people were feeling some desire when their phones went off—to snack, to goof off, to express their true feelings to their bosses—and another quarter said they had felt a desire in the past half-hour. Many of these desires were ones that the men and women were trying to resist, and the more willpower people expended, the more likely they became to yield to the next temptation that came along.

The results suggested that people spend between three and four hours a day resisting desire. Put another way, if you tapped four or five people at any random moment of the day, one of them would be using willpower to resist a desire. The most commonly resisted desires in the phone study were the urges to eat and sleep, followed by the urge for leisure, like taking a break from work by doing a puzzle or playing a game instead of writing a memo. Sexual urges were next on the list of most-resisted desires, a little ahead of urges for other kinds of interactions, like checking Facebook. To ward off temptation, people reported using various strategies. The most popular was to look for a distraction or to undertake a new activity, although sometimes they tried suppressing it directly or simply toughing their way through it. Their success was decidedly mixed. They were pretty good at avoiding sleep, sex and the urge to spend money, but not so good at resisting the lure of television or the Web or the general temptation to relax instead of work.