Hunger increases and thirst decreases due to salty food

In a study carried out during a simulated mission to Mars an international group of scientists has found the idea that salty foods make you thirsty to be nothing but an old wives tale

They discovered that a diet higher in salt did not necessarily equate with increasing a person's thirst or the level of urine produced, at all, but instead caused the test subjects to feel hungrier. Increased levels of glucocorticoids are an independent risk factor for diabetes, obesity, osteoporosis and cardiovascular disease. Consuming salty foods did not make them thirsty; rather they became more hungry. However, after putting this theory to the test, researchers have shown the opposite to be true.

It was previously thought that the extra fluid simply came from drinking, but researchers from the German Aerospace Center (DLR), the Max Delbrück Center for Molecular Medicine (MDC), Vanderbilt University and their colleagues have proven otherwise.

However, synthesising urea takes a lot of energy, which explains why mice on a high-salt diet were eating more, researchers said. Well nearly same diets were given to the two groups, only difference in their diet being in that over periods lasting several weeks, they were given three different levels of salt in their food.

The first batch was studied for 105 days, while the second one was examined over 205 days. The fact is that a salty diet led to less quantities of liquid drank by the astronomers, and salt was triggering a mechanism for conserving water in their kidneys. These new results show that salt stays in the urine, leaving water to move back into the body.

While there is not a definite answer to this puzzling mechanism, researchers believe that the urea could be involved. Similarly, the men in the cosmonaut study who were on a high-salt diet complained of hunger. "In addition, salt can induce a glucocorticoid-driven catabolic state with increased urea osmolyte and metabolic water generation", noted the research.

"We now have to see this process as a concerted activity of the liver, muscle and kidney", said Jens Titze, of the University of Erlangen-Nürnberg and Vanderbilt University Medical Center. This happens because the body uses the fluid to create energy, which then produces carbon dioxide and water that the body can rid itself of.

Crew members try out their spacesuits during a simulated mission to Mars at the Russian Academy of Sciences' Institute of Biomedical Problems (IBMP) in Moscow.

The original hypothesis stated that charged sodium and chloride ions contained in salt from water molecules were dragged into the urine.

In mice, urea was accumulating in the kidney, where it counteracts the water-drawing force of sodium and chloride. These results puzzled the scientists as nobody expected a study about Mars to conclude that salty foods increase a human's appetite and decrease their water consumption on the long term.

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