It is obvious to anyone who likes bacon or potato chips that salty foods make you thirsty. But in the long term, you actually become less thirsty because your body starts to conserve and produce more water, a surprising new study has found.
The counter-intuitive finding, by scientists at Vanderbilt University and in Germany, could shed new light on the Western epidemics of obesity, diabetes and heart disease.
Biology 101 will tell you that the excretion of dietary salt inevitably leads to water loss into the urine, thereby reducing body water content. But that is not what the researchers found.
In fact, to the contrary, they showed that the biological principle of salt excretion is actually water conservation and water production.
Long-term Sodium Balance
The researchers conducted a simulated mission to Mars between 2009 and 2011, investigating long-term sodium balance. Unexpectedly, when dietary salt was increased from six to 12 grams a day, the men participating in the study drank less water, not more. That suggested they conserved or produced more water.
It takes a lot of energy to conserve water in the face of salt excretion. To do it, the body either must take in more fuel or break down muscle mass. This predisposes to overeating, according to the reports’ senior author, Jens Titze, M.D., associate professor of Medicine and of Molecular Physiology and Biophysics.
In a later study using mice, the researchers demonstrated that high salt induces a catabolic state driven by glucocorticoids that breaks 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 also have other pathological consequences. Increased levels of glucocorticoids are an independent risk factor for diabetes, obesity, osteoporosis and cardiovascular disease.
Funding for the work was provided by the Federal Ministry for Economics and Technology/DLR; the Interdisciplinary Centre for Clinical Research; the NIH; the American Heart Association (AHA); the Renal Research Institute; and the TOYOBO Biotechnology Foundation.