New York is the first city in the US to add sodium warnings to menus

For years, New York City has served as a petri dish for public health experiments. The city was the first to ban trans fats and the first to mandate calorie menu labeling at restaurants. Now New York will also be the first US city to tackle excess salt consumption with new menu labels.

(New York Department of Health)

Starting December 1, all chain restaurants with 15 or more locations nationwide will have to post a little salt shaker symbol next to menu items that contain more than 2,300 milligrams of sodium (about a teaspoon worth). Restaurants will also be required to warn consumers that eating a lot of salt can increase the risk of heart disease and stroke.

But will this initiative actually encourage people to eat healthier? Probably not. Based on the research we have on calorie menu labeling, this experiment likely won't have a huge direct impact ... though it could have smaller indirect effects.

Here's why. First, the rule only applies to foods that are wildly, excessively salty. To put this in context, 2,300 milligrams is the daily recommended limit for total sodium consumption. New York's law will only apply to individual foods that reach that level all by themselves. Why the city didn't set a lower warning threshold is unclear, but it means the labels will miss all the heavily salted foods that stay under that limit — like the meatball sandwich at the Olive Garden shown here, which contains nearly a day's worth of sodium:

The rule is also limited in another way: It'll only apply to bigger chain restaurants, which the health department estimates captures about 10 percent of the restaurant foods people eat. So New Yorkers may now get a quick sense of whether their Panera sandwich is too salty, but they won't know if there's a load of salt in the meals they buy at their local sushi bar every week.

Finally, it's not clear that menu labeling actually has any impact on health outcomes. The best evidence we have on the question relates to calorie labeling, and it's pretty mixed. It appears that people who are already calorie-conscious do pay attention to labels, but those who aren't don't. In other words, just having that information displayed doesn't change people's behaviors.

That said, the sodium label could have a few indirect consequences. In particular, newer research has suggested that calorie labeling can compel chains to cut the number of calories in their fare. Maybe the sodium labels will have the same result. And at the very least, it's a step toward transparency and giving people a better sense of what's in the food they're eating.

And in case you're wondering, about how much salt to eat, the best science tells us this: a very high sodium diet (two teaspoons or more of salt each day) is probably harmful; a very low sodium diet (less than one teaspoon per day) may also be harmful; one teaspoon (or 2300 mg) seems to be just right for most people.

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