Salt may be at the heart of a dietary disagreement, but it’s also the main ingredient in a billion-dollar American industry.

The United States is second in the world for producing salt for various purposes, ranking behind only China. Together, the two countries produce more than 40 percent of the world’s salt each year, according to the Salt Institute, a nonprofit trade association.

In 2012, the United States produced 40.2 million metric tons of salt, according to the U.S. Geological Survey. While that amount is 11 percent lower than what the country produced in 2012, it still had a value of more than $1.6 billion.

And any changes in dietary recommendations, or in Americans’ eating habits, will have a negligible effect on the salt industry. Salt meant for food processing accounted for only 4 percent of sales last year, according to the Geological Survey. Rock salt put down for de-icing roads accounted for 41 percent of last year’s total salt sales, while the chemical industry made up 39 percent of sales.

The United States has plentiful salt reserves in underwater domes, salt veins and other underground deposits. According to the Geological Survey, 28 companies operated 67 salt plants in 16 states in 2012.

Some of the top salt-producing states are Kansas and Utah, which have large underground deposits; Louisiana, which can access underwater salt domes in the Gulf of Mexico; and Ohio, Michigan and New York, which have major deposits in the Great Lakes.

Aside from underground mining, salt producers can also use solar or vacuum evaporation to collect salt — all methods used in the United States. In vacuum evaporation, large commercial evaporators use steam heat to evaporate salt brine and leave salt crystals. In the solar method, saline water is captured in shallow ponds, and the sun naturally evaporates the water over a long period of time, leaving beds of crystallized minerals. Producers then cleanse, harvest and process the minerals.

Salt is also a fairly stable commodity. Nearly every country in the world has salt deposits or solar evaporation operations with which to get salt, the U.S. Geological Survey said.

“World continental resources of salt are practically unlimited, and the salt content in the oceans is virtually inexhaustible,” the agency said in a recent report.