Many New Year’s resolutions involve healthy eating or losing weight. Most of these resolutions are generally unsuccessful. Why? People eat more after the holidays.

Americans purchase about twice as many calories (per serving) in food during the first three months of the new year than during the holidays, according to a new study published in PLOS ONE.

In the study, researchers tracked the grocery spending habits of more than 200 homes in New York for seven months.The results were separated into three periods—a baseline period (July to Thanksgiving) a holidays period (Thanksgiving to New Year's) and a post-holidays period (New Year's to March).

Researchers found that Americans buy about 440 extra calories per serving during the holidays. After the holidays, they buy an additional 450 calories per serving.

"People start the New Year with good intentions to eat better," Professor Lizzy Pope of University of Vermont’s Dept. of Nutrition and Food Science, told Science Daily. "They do pick out more healthy items, but they also keep buying higher levels of less-healthy holiday favorites. So their grocery baskets contain more calories than any other time of year we tracked."