Asking your server one question could keep you from calorie overload.

Unless you're in your own kitchen, controlling how much food you're served is nearly impossible—and portions at restaurants have only grown over the years—so much so that "standard" dinner plates in America are now three inches larger than they were a century ago.

When it comes to eating healthy while dining out, there are plenty of tricks that dieters use. But the best hack may be asking for a takeout box before you even start eating, according to new research.

A new study, published in the October issue of the research journal Appetite, finds that diners who ask for a to-go box while ordering actually have better chances of keeping portions reasonable. Researchers from Pennsylvania State University split female test subjects into two groups—those who were informed that uneaten food would be immediately packaged to take home at the beginning of the meal, and those who weren't given this option—and served them dishes of various sizes to see how diners would respond.

Interestingly, those who were not told they were being sent home with leftovers ate more food, even as the meal's size increased—even when portions were 75 percent larger than the baseline.

Overall, the research found that the control group consumed a significantly higher number of calories over those who were given takeout boxes. They concluded that "packaging uneaten food after a meal could be an effective strategy to reduce overconsumption from large portions."

More tips to help you practice good portion control:

While the new research doesn't provide a definitive scientific reason for why those who took leftovers home ate less, it could be that some diners may feel that they're wasting food (and money spent on it) if they don't finish every bite on their plate. It seems that just knowing you'll be able to eat the rest later makes a person unconsciously less concerned about eating it all now—and more willing to listen to your own body's cues when it comes to fullness. (Here's what happened when one writer stopped trying to eat healthy—and started listening to her body.)

If you are watching your calorie intake, try asking for a to-go container at the beginning of the meal, and see if makes a difference.