OTTAWA—Tucked into the controversial U.S. health care legislation signed into law in March 2010 is a provision requiring restaurant chains to post the caloric punch behind their offerings.

This isn't a matter of burying illegible lists in 5-point font on the restaurant's website, visited only by people doing research reports on fattening restaurant foods. Calories must be posted as prominently as the price, be it in the menu booklet or on the menu board. Restaurants need to abide by the law by 2011.

So, unless stricken by nutritional deficiencies from eating fast-food every day that have left you blind or befuddled, you soon will plainly see that Sbarro's fettuccine alfredo with grilled chicken contains over 3,000 calories, a single meal that could feed six adults.

Will this make a difference on what people choose to eat or avoid? The answer, according to researchers at an international nutrition meeting here the last week of October, sponsored by the Center for Science in the Public Interest, is a resounding maybe.

Partial solution

"Calorie posting is no silver bullet," said Phillip Leslie, an economics professor at Stanford University who reported unpublished results on Starbucks. The coffee chain began posting calories on menus in New York City in accordance with a local law enacted in 2008.

Leslie's study analyzed 110 million transactions before and after the law went into effect. Consumers' beverage choices remained the same, but food calories fell by 14 percent.

Considering, however, this was only a 14-percent decrease in calories not necessarily consumed daily, the overall impact of calorie posting nationwide would lead to a mere 30-calorie reduction in a 2,000-calorie-a-day diet, according to Leslie's back-of-the-envelope calculation.

But the effect could be larger for other restaurant chains, Leslie said; it's too soon to tell. The law is just one, albeit meaningful, element of the needed calorie-awareness campaign, he said.

Two-way street

In light of such uncertainty over the law's effectiveness, you would think that restaurants are up in arms. They were. The New York State Restaurant Association sued New York City in 2007. They lost, appealed and lost again.

The reason for defeat, cited by the courts, was that eating out is associated with obesity and that consumers are clueless about calories in restaurant food. Posting calories would enlighten consumers about what they think are healthier alternatives, too, and they would learn "that a smoked turkey sandwich at Chili's contains 930 calories, more than a [11-ounce] sirloin steak... or that 2 jelly-filled doughnuts at Dunkin' Donuts have fewer calories than a sesame bagel with cream cheese," according to Second Circuit Court of Appeals ruling.

Restaurant associations were fighting losing battles nearly everywhere they challenged a local law. Seeing the writing on the wall, they approached Congress to create a national standard so as not to be burdened by a patchwork of local requirements. The National Restaurant Association indeed supports the 2010 national law.

Not enough

While prominent postings of calories would enlighten diners and perhaps serve as catalysts for restaurants to serve healthier fare, many factors conspire to make the law less effective, according to Yoni Freedhoff, founder and medical director of Ottawa's Bariatric Medical Institute.

Freedhoff critiqued numerous studies that showed minimal effects of menu labeling. One problem is that "marketing trumps menus," he told conference participants. So while it may be true that consumers ate more calories at Subway after the law in New York City, this was because Subway had introduced a new deal for foot-long subs, longer than the typical sandwich.

Elsewhere, Freedhoff demonstrated that calories often are understated by as much as 18 percent. But ultimately, stating whether a food item has 100 or 1,000 calories means little if consumers don't know that most adults need only about 2,000 calories a day.

"Calories abhor a vacuum," he said. "We need to provide people with not only calories but also an understanding of energy balance."

It will be an uphill battle, for sure, but at least we'll all burn some calories.

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Christopher Wanjek is the author of the books "Bad Medicine" and "Food At Work." His column, Bad Medicine, appears regularly on LiveScience.