The Obama administration is pressuring the food industry to make foods from breads to sliced turkey less salty, proposing long-awaited sodium guidelines in an effort to prevent thousands of deaths each year from heart disease and stroke. The proposed guidelines released Wednesday are voluntary, so food companies won’t be required to comply. But the idea is to persuade companies and restaurants — many of which have already lowered sodium levels in their products — to take a more consistent approach. […] Some companies have worried that though the limits will be voluntary, the FDA is at heart a regulatory agency,...