McDonald's announced Wednesday that it would get a head-start on an Affordable Care Act provision that requires all chain restaurants to provide calorie labels on menus. Those new labels will go up as soon as next week.

The comprehensive plan aims to help customers and employees make informed nutrition choices whether visiting McDonald's or eating elsewhere.

"At McDonald's, we recognize customers want to know more about the nutrition content of the food and beverages they order," said McDonald's USA President Jan Fields. "As a company that has provided nutrition information for more than 30 years, we are pleased to add to the ways we make nutrition information available to our customers and employees."

Some of the nutrition facts may be startling. It turns out, for example, the highest calorie item at McDonalds is not a burger but rather the 16-ounce M&M McFlurry. With 930 calories, it has about half the calories that the Food and Drug Administration recommends a woman should eat in a single day. It's equal, in calorie content, to three McDonald's cheeseburgers.

So, surprises may abound. But will it change eating habits? New York City has had calorie labels on all chain menus since 2008. The evidence is mixed, but tends to lean against these changes having a significant public health impact.

One 2008 study, conducted by Brian Elbel, Rogan, Kersh, Victoria Brescoll and L. Beth Dixon, compared the eating habits of New York City residents with those of Newark, a nearby city that did not implement calorie labels. New York City residents certainly noticed the new calorie labels much more than those tiny-print pamphlets fast food chains often leave out. And a handful even indicated that they would buy fewer calories after seeing those labels.

But at the end of the day, they didn't follow through. New York City residents studied here, who came from low-income demographics, purchased the same amount of calories before and after the labels came online. You'll notice a slight uptick in the chart below, although the authors note it's statistically insignificant.

"About half of the NYC respondents in our postlabeling sample reported noticing calorie information, and only a quarter of these reported that the information influenced their food choices," the study authors write. "Even those who indicated that the calorie information influenced their food choices did not actually purchase fewer calories according to our data collection."

A more recent study, conducted by the New York City Department of Public Health, was more promising. The city collected receipts from 15,000 customers at coffee shops and fast food restaurants one year before and after the labels went up.

Overall, it showed no difference in calorie consumption. Only 15 percent of the customers they talked to reported using the labels to make a purchasing decision, a number in line with the prior study.

Among that sub-population, however, this study did find a change: They purchased 96 fewer calories than the average customer, translating into a meal that was 11 percent smaller. The decline was most notably at Domino's, where consumers ate 280 fewer calories, on average, after the menu labels came into effect.

What does this mean for the Affordable Care Act? Earlier this year, a team of University of Minnesota researchers tackled that exact question.

They outfitted two restaurants with calorie-listing, mimicking what would happen when the Affordable Care Act regulation takes effect, albeit at a smaller level. While they saw a small decline at the very start of the intervention, "by the end of the study there was no difference."

One obstacle menu-labeling might be a knowledge gap: Most people just don't know how many calories they're supposed to eat in a single day. The International Food Information Council Foundation did a survey earlier this year, and found only one out of seven Americans - 15 percent - could accurately estimate the number of calories they need to consume to maintain their weight. If you don't know how many calories to eat in one day, information about calorie levels might not prove an especially informative tool for decision making.