Exercising more, spending less, volunteering—for many people, New Year's is a time for reflecting on past actions and resolving to do better. One of the most popular vows is to eat healthier after the extended holiday gluttony. But a study of grocery store habits reveals that many of us may try to fulfill that resolution by simply buying more healthy foods, all the while consuming non-healthy eats at the same belt-stretching holiday levels.

That means many families actually buy more food week to week in January—both in dollar value and weekly per-serving calories—than they do during the festive season between Thanksgiving and New Year's.

The usual assumption is that people put on weight over the holidays and then resolve, but often fail, to take the proper actions to eat better in the New Year. But is that actually the case? “We wondered if the food that people are actually purchasing matches up with the goals that many are setting,” says Lizzy Pope of the University of Vermont.

Working with a major regional grocery store chain in upstate New York, Pope and her colleagues tracked the food purchases of 207 participating households during the holiday period (Thanksgiving to New Year's), the post-holiday period (New Year's to March) and a baseline period (July to Thanksgiving).

Pope's team used the chain's own proprietary food rating system to measure healthy versus junky purchases. The store ranks foods on a scale of zero to three, from those with no nutritional value like soda (a zero) to nutritional powerhouses like fresh fruits and vegetables (a three).

Predictably, buyers made plenty of non-healthy choices during the holiday period, a time known for festivity, feasting, giving to others and a good bit of self-indulgence. Household food expenditures rose 15 percent over the baseline ($105.74 to $121.83), and three-quarters of that increase was represented by the purchase of less-healthy foods, the team reported this month in the journal PLOS ONE.

“We expected those results,” says Pope. “But we were surprised by what happened after the holidays. We hear so many people say they will eat healthy, and in fact they do purchase more healthy food during that period. But we saw no decrease in the amount of unhealthy food that they buy.”

During the post-holiday period, sales of healthy foods spiked by 18.9 percent above the holiday period and nearly 30 percent above the baseline. But sales of less-healthy foods continued unabated at holiday levels. The addition of healthier purchases to less-healthy buying meant that weekly per-serving calories purchased actually rose after New Year's by some 9 percent.

The data don't provide a direct answer as to why shoppers followed this pattern, but they did suggest a few theories to Pope and her colleagues: “Psychologically, it may feel like you're fulfilling your resolution to eat well when you're buying all that healthy food, even though you are still consuming all that unhealthy food that you did during the holidays,” she says.

Another possibility is that continued buying of less-healthy items serves as a way to combat the post-holiday blues. “During the holidays you get into a habit of needing to buy certain foods that you weren't buying before,” she theorizes. “After the holidays are over, there's a sense of loss for many people already, so to have to stop buying those fun and special tasty foods can compound that. So if you can add the healthy foods on top of those purchases, you kind of reach a nice psychological balance where you are fulfilling your goals but not feeling a loss in terms of the tasty foods.”

For now the data also don't explain when, or if, food purchasing returns to the previous year's baseline. The team didn't measure purchases from March to mid-July, so it's unclear if purchasing of healthy or less-healthy foods drops during that time.

“We hypothesize that maybe bikini season comes upon people, especially in regions like the Northeast where that is a big thing, so they start to pay really close attention to what they are eating in the lead-up to those summer months,” Pope says. In that case, spring and summer would be the period when many people hit the “reset” button on their eating lifestyles, rather than via those much-ballyhooed New Year's resolutions.

The team suggests another theory as well, one less comforting for those concerned about America's hefty caloric intake: “What could also happen is that every year we just eat a little bit more,” Pope says. That may account for why people gain a small amount of weight every year, the 1 to 2 pounds which is documented in some studies. People could also be wasting a bit more food each year—the study traced household purchasing and not actual food consumption. But previous research has shown that food-purchasing data offer an accurate record of consumption.

Next steps may include looking at regional differences in these patterns between upstate New York and cities such as Southern California, Seattle or San Antonio.

“In Southern California, people have access to amazing fresh fruits and vegetables almost all the time, versus in New England, for example, where there are more seasonal variations. But we still see obesity in southern California,” Pope says. “I think that these findings would most likely translate across regions, but it would be very interesting to look at that and try to find out.”

What she would most like to do, however, is collect enough data to suggest strategies that can actually help people eat healthier. Part of that is the study of psychological forces behind what people buy, while another piece is finding the right practical strategies for shoppers.

“Does it help if you create a list and really stick to that list? Or can you divide the cart into areas, like one half for fruits, vegetables and whole grains and the other for less-healthy foods," says Pope. "It may be that just delineating how much of the cart to fill with each type of food helps to impact what people are purchasing.”