Diet Soda Is Bad for Decision Making—Here's What's Good

Study: To improve concentration and make better decisions, your brain needs enough glucose.

January 29, 2010

Can't decide? Feed your brain.

RODALE NEWS, EMMAUS, PA—The amount of sugar in your blood could be a key factor in the decisions your brain makes, according to new research. While previous studies have linked blood glucose levels to how we process our thoughts, new research out of the University of South Dakota suggests low glucose levels could be related to lack of self-control and impulsive decision making. The good news is that improving concentration could be as easy as knowing what to eat and drink—and what not to—when it's decision time.


THE DETAILS: Researchers investigated how blood sugar (glucose) levels affect a person's self-control, specifically how people thought about immediate versus future rewards. Participants were asked questions to determine if they would prefer to get a smaller amount of money right away (indicating a lack of self-control) or a larger sum of money later on. Researchers tested blood glucose levels, and asked the questions, before and after the participants drank either a regular sugar-sweetened soda or a sugar-free, artificially sweetened diet soda. The sugar-free soda drinkers were more likely to choose the immediate reward, even though it was less money and not the best overall decision. The results indicate that when people have more energy available—as evidenced by the levels of glucose in their blood—they are more future-oriented. On the other hand, having low energy or low blood glucose levels may make a person focus on the present. In fact, the authors go on to say that artificial sweeteners may signal to the body that there's an imminent caloric crisis, leading to increased impulsivity. If this is true, controlling blood glucose levels could offer a possible intervention for impulsive disorders, anorexia, and drug and gambling addictions. The take-home message for general readers is three-fold, says study author XT Wang, PhD, professor of psychology at University of South Dakota."First blood glucose may strengthen self-control by making future rewards more attractive and reduce impulsivity. Second, our body can detect artificial sweetener in a diet soda and react to this 'energy crisis' by grabbing immediate resources available and discounting delayed rewards," he explains. "Third, carefully regulating blood sugar and avoiding sharp fluctuations might be a means of treatment for a range of impulsive disorders, including addictions."

The study was published this month in the journal Psychological Science.

WHAT IT MEANS: First off, this study isn't about whether you should drink diet or regular soda before making an important decision. In fact, neither is a particularly healthy choice (water is the best option for your body). The real message is to feed your brain what it needs in order to calculate with sound judgment. Maintaining adequate glucose levels when you have a decision to make—whether it's a tough business decision at work or a difficult personal choice like should you really drop $200 on a pair of shoes—will help prevent you from making impulsive decisions, and make it easier to weigh the long-term consequences of your choices. If you're wondering if this pertains to overeating, it does. "Low blood sugar leads to quick decisions to replace sugar, so a candy bar may look more appealing than when the blood sugar is not low," explains Christine Gerbstadt, MD, RN, spokeswoman for the American Dietetic Association.

That means if you eat a piece of fruit before going out to eat, you're in a better position to make a healthy decision when you order, and to not overeat. "Remember Scarlett O'Hara in Gone with the Wind? She ate before her date to not overeat in front of her beau," says Dr. Gerbstadt. "The idea is small, frequent meals may ward off bingeing or overeating."

When improving your concentration is critical, here's how to feed your decision maker for the best results.

• Get most of your glucose from complex carbs. The brain needs glucose to function, but too much over a long period of time can lead to insulin resistance and diabetes. Of the carbs you get in a day, only 10 percent should come from simple sugar. The rest of your carbs should come from complex carbohydrates like vegetables, whole wheat, brown rice, corn, and other grains. For a typical 140-pound 30-year-old woman, for example, 600 calories from carbohydrates is a healthy goal (or more, if she's active). [Clarification: 600 Calories of carbs is a safe, minimum amount for a woman of that weight and age who's not very active. --the editors.] Of this, no more than 10 percent, or 60 calories, should come from simple sugars. That's equal to four teaspoons of sugar, much less than you'd get from a can of soda.

• Feed your brain early. Got a big presentation at work or a huge test coming up? Don't chug a soda beforehand to improve concentration, but rather start thinking about your carb intake a few days earlier. For a stressful situation that requires lots of brainpower, "the diet should contain lots of complex carbohydrates and whole grains for two days before the event," explains Dr. Gerbstadt. "It's kind of like carbohydrate-loading in endurance athletes." Swig some water instead of that soda. "Even slight dehydration of just 1 percent can cause decrease in mental acuity," she says.

For your meal prior to a stressful decision-making task, eat a light meal that's low in fat—too much fat will direct more blood to your stomach instead of your brain.

Next Up From Rodale Wellness

How She Beat Depression Driven Eating to Lose 50 Pounds
Nikki Marshall had lost all faith in beating obesity, until she found running.
She Lost More Than 150 Pounds by Learning Portion Control
These days, Kate McPhail looks at ice cream a lot differently than she used to.
How Eating Pizza Helps You Lose Weight
Discover how breaking your diet could be the one thing that helps you stick to it.