- The biological principle of salt excretion is actually water conservation and water production.
- To conserve water, the body must either take in more fuel or break down muscle mass.
- High salt induces a catabolic state driven by glucocorticoids that break down muscle protein.
- Increased levels of glucocorticoids are an independent risk factor for diabetes, obesity, heart disease.
After eating salty food, we usually get thirsty and drink water. But within 24 hours, we actually get less thirsty because the body starts to conserve and produce more water.
Thee body's response to high salt intake could provide an entirely new approach to the three major killer diseases- diabetes, obesity and heart disease.
Salt Conserves Water in the Body
It takes a lot of energy to conserve water in the face of salt excretion. The body either must take in more fuel or break down muscle mass. "This predisposes to overeating," said the reports' senior author, Jens Titze, M.D., associate professor of Medicine and of Molecular Physiology and Biophysics.
High Salt Diet Induces Hunger, Food Intake
Between 2009 and 2011, Titze and his colleagues conducted long-term sodium balance studies in Russian cosmonauts who were participating in a human space flight simulation program at a research facility in Moscow in preparation for a potential manned spaceflight to Moscow.
Unexpectedly, when dietary salt was increased from six to 12 grams a day, the men drank less water, not more. That suggested they conserved or produced more water.
In a subsequent study in mice, the researchers showed that high salt induces a catabolic state driven by glucocorticoids that break down muscle protein, which is converted into urea by the liver. Urea enables the kidneys to reabsorb water and prevent body water loss while the salt is excreted.
Muscle wasting is a high price to pay for avoiding dehydration. The alternative is bringing in more fuel - eating more. That may be why the men in the study complained they were hungry.
Water conservation in response to a high-salt diet may have pathological consequences. Increased levels of glucocorticoids are an independent risk factor for diabetes, obesity, osteoporosis and cardiovascular disease.
"We have always focused on the role of salt in arterial hypertension. Our findings suggest that there is much more to know -- a high salt intake may predispose to metabolic syndrome," Titze said.
- Jens Titze et al., Vanderbilt-led study shows high-salt diet decreases thirst, increases hunger, Journal of Clinical Investigation (2017).