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There are two conditions under which animals, including humans, choose to consume salt. The first, which has been widely studied in experimental animals, occurs when there is a true sodium need, such as experienced by many plant-eating animals that live in low-sodium environments. This is called salt need (Denton, 1982; Geerling and Loewy, 2008). A number of hormonal, central nervous, and behavioral systems are engaged when an animal is truly deficient in sodium, which motivates it to search for sodium salts, avidly consume them based on their salt taste, and thereby restore sodium balance (Morris et al., 2008). Sodium-depleted animals have an innate ability to recognize, by its distinct taste, the needed nutrient. Although true sodium need may be experienced by humans under some conditions and has been studied experimentally (Beauchamp et al., 1990; McCance, 1936), it is a very rare occurrence under most circumstances. It thus cannot explain why humans consume as much salt as they do (Beauchamp and Stein, 2008; Leshem, 2009). A marginal deficiency of other minerals, particularly calcium, may play a role in stimulating human salt intake (Tordoff, 1992). If this proposed relationship is supported in further studies, it would suggest that one strategy to reduce salt liking and perhaps intake would be to encourage increased calcium consumption, which is already strongly recommended for bone health (HHS, 2000).

The second condition responsible for salt intake occurs in many species, including humans, even when there is no apparent need for salt—that is, when sufficient sodium for all bodily needs has been consumed. This has been termed salt preference (Denton, 1982), even though the desire does not reflect a conscious preference. Taste preference for salt (in the absence of need) has been identified in many animals. Humans generally consume far more salt than is actually necessary and continue to enjoy salty foods even when physiological needs are met. Thus, it appears that salt preference rather than a true physiological need drives salt intake in human populations. Why people consume so much more salt than they need is a concept that is not fully understood and needs explanation.

It has been argued that a preference for salt beyond physiological need is due primarily or exclusively to learning, particularly early learning, or even that it is an addiction (Dahl, 1972; MacGregor and de Wardener, 1998; Multhauf, 1978). In contrast, other investigators have argued that while learning may play a role, evolutionary pressures to consume salt have shaped people and some other animals to have an innate liking for its taste, even when sodium is not needed (Beauchamp, 1991; Denton, 1982). Denton (1982) noted that merely because salt is consumed in excess of contemporaneous need in no way mitigates against such consumption being driven by innate propensities, just as sexual activity occurs in the absence of intent to increase numbers of the species. Even under the first hypothesis, which proposes that high salt intake is due to powerful learning, salt

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