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At the heart of the salt debate is a medical mystery. Salt may contribute directly to hypertension, but nobody knows exactly how. Sodium chloride is essential to all living things. The tissues of the human body are constantly moistened by a briny solution thought to be of about the same salinity as the primordial sea from which life emerged. As Hayes puts it, we are "miniature oceans encased in skin." The balance of salt to water in that internal ocean must be carefully maintained: virtually all vital functions, including nerve impulses and heart action, depend on it. Keeping that proper balance is mainly the work of the kidneys. The healthy body needs, and can use, only about 200 mg of sodium per day. Anything more is excreted by the kidneys in order to keep balance. "The human body has a tremendous capacity to get rid of salt," explains Physiologist Arthur Guyton of the University of Mississippi School of Medicine at Jackson. Though it is unwise to do so for long, Guyton notes, "most people can load up on salted junk food and excrete twelve times their normal sodium intake in just a few days with no ill effects." Only in hypertensives, for reasons as yet unknown, does too much salt mean trouble.
A problem in kidney functioning is almost certainly at fault, and the trouble is probably inherited. It seems to run in families and in races. Blacks, for example, are twice as likely to have hypertension as whites. No matter how much salt is used, only certain individuals will develop hypertension; an estimated 20% to 40% of the population is susceptible. Still, "it is very difficult to determine in advance who is and who isn't sensitive to salt," says Dr. Allan Forbes of the FDA. "That's why many medical experts believe it is reasonable to modify the sodium intake for everyone."
While it seems prudent for the U.S. to keep the salt load light, antilabeling forces can, and do, complain that any Government action would expensively penalize industry and force upon an uninterested majority rules and reforms desirable only to a minority. Most people like salt, says William Dickinson, president of the Salt Institute, which represents salt processors in the U.S. and abroad. "It's easy to say cut back, but food just doesn't taste good without it. If we eliminate salt, we'll just see a lot more processed food being scraped into the garbage can." Dickinson also thinks that any labeling that singles out sodium is "scare labeling." He opposes it unless "all other nutrients of concern to the consuming public" are labeled as well. Adds Dickinson: "Who says sodium is more important than excess fats or calories?"
Food processors also point to the difficulty of determining the sodium content of many products. Pretzels are a problem, they say, because nobody knows how much salt actually sticks to the pretzel and how much comes off in the bag. Cost is a problem too. The Center for Science in the Public Interest claims that the cost of labeling will be less than 1% of the price of the product, and in most cases less than .5%. But according to General Foods, the cost of its voluntary labeling so far has proved "not insignificant." If done across the board, it might drive food prices up considerably.