Consumption of salty food by rats: regulation of sodium intake?

The extent to which sodium levels may be regulated by consumption was examined in two experiments that offered rats foods varying in sodium chloride (NaCl) content. In the first, rats received single purified diets containing from 0% to 3% NaCl. There were no effects of NaCl level on the amount or pattern of daily food intake; water intake, however, increased with salt content. In the second study, rats had choices between a NaCl-free food and a food containing either 1, 2, or 3% NaCl for 1 week each. Total food intake was unaffected. Proportional intake of the salt-free option increased with the salt content of the alternate food, but not sufficiently to maintain a constant NaCl intake. After 8 weeks of exposure to a single food, intake of the salty option increased in the choice tests, but the level of NaCl (from 0.5 to 3.0%) in the exposure-phase food did not affect the subsequent choice. We conclude that when only one food is available, salt intake is governed by caloric requirements and sodium levels are regulated by excretion. When foods differing in NaCl content are available, consumption does contribute to the regulation of sodium balance, but the amount consumed is not tightly controlled. Rats' salt preference appears to increase with age or with experience eating the purified foods offered here, but experience eating salty food does not affect the preferred level of salt.