If your New Year’s resolution is to eat healthier, you should be taking control of your food—in the literal sense. A new study finds that if you serve yourself, you eat smaller portions of junk food and desserts, as the Science of Us and The Wall Street Journal report. The study, led by USC marketing researcher Linda Hagen, found that the more people are physically involved in serving their food, the less interested they are in unhealthy snacks.

The researchers tested their hypothesis out over the course of five tests. In one, they invited students to help themselves to either dried fruit or Reese’s Pieces off a table. Sometimes, the table setup required students to scoop their own snack out of a bowl, while other times, the cups were already set out with 45-gram portions of the snack. The researchers later measured how much of the snacks in bowls or cups had been taken. In another test, people rated how healthy they felt after eating certain snacks, either pre-portioned or not.

Overall, the researchers found that participants were more inclined to choose large portions of unhealthy food if they didn’t portion the snacks out themselves. But there was no effect when people served themselves healthy food.

Eating choices affect how people see themselves, so when people choose to eat unhealthy foods, they feel bad about themselves. Previous research has found that eating in front of a mirror can help make people enjoy dessert less, since people have to confront their own choices in an immediate way. The researchers found that people felt less responsibility for their choices when served by someone else, and thus they felt better about eating unhealthy food.

However, slicing your own cake isn’t the only way to make healthier choices. Other studies have found the best way to increase self control is not to exercise greater willpower in the face of temptations but to take away those temptations altogether. So put away the pie. But if you must, don’t let anyone else slice it for you.

[h/t Science of Us]