New research suggests that people buy the greatest amount of food and calories after the holidays, despite New Year's resolution to eat healthier and lose weight.

A group of researchers led by Lizzy Pope of the University of Vermont found that consumer spending on food increases by 15 percent over the holiday season (Thanksgiving to New Year), with most of the increase attributed to higher levels of junk food. But shoppers buy the greatest amount of food after New Year -- the equivalent of a 9 percent increase in calories above holiday levels.

"People start the New Year with good intentions to eat better," Pope said. "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."

For the study, researchers recruited more than 200 households in New York State to participate in the seven-month study of grocery store spending behaviors, from July 2010 to March 2011.

To identify shopping patterns, researchers split the data into three periods: July to Thanksgiving represented participants' baseline spending (how much the average shopper regularly spends per week on groceries), Thanksgiving to New Year's was considered the holiday season, and New Year's to March the post-holiday period. They also categorized food as healthy or less healthy based on a nutritional rating system used at participating grocery stores.

Researchers said their findings are surprising given the holidays' reputation for overeating -- and suggest that people need better strategies for shopping under the sway of "res-illusions."

The researchers recommend that consumers use written grocery lists to deter impulsive junk food purchases; substitute as much junk food as possible with fresh produce and nutrient-rich foods, and split grocery baskets visually to ensure nutritious foods represent at least half of your purchases.

The findings are detailed in the journal PLOS One.