According to a team of researchers at Berlin’s Max Delbruck Centre for Molecular Medicine (MDCMM), when dietary salt levels increased, dehydration and thirst actually decreased significantly.
Salt intake is thought to increase fluid intake – a factor the World Action on Salt and Health (WASH) suggested contributes to the obesity crisis, as salty foods could increase public consumption of soft drinks.
Whilst a highly salty diet may reduce thirst and decrease consumption of sugary soft drinks, the team also found it could contribute to fatty food consumption.
The researchers acknowledged an increase in hunger and food intake “may link high salt intake with diabetes mellitus, osteoporosis, and increased cardiovascular and neurovascular disease risk”.
The study has faced criticism from others in the scientific community however. Professor Graham MacGregor, Professor of Cardiovascular Medicine at Queen Mary University of London and Chairman of the UK's Consensus Action on Salt and Health (CASH), told FoodNavigator:
"It is well established that increasing salt intake increases thirst and increases fluid intake. Many studies have shown a clear relationship between salt intake and fluid consumption. This new, complicated, study does not change these conclusions, but does suggest that under certain (rather contrived in our view) circumstances there may be long term fluctuations in salt and water balance. This study does not in any way question the overwhelming evidence that increased salt intake leads to high blood pressure, which is the major cause of strokes, heart disease and kidney disease."
Campaigns and pressure groups for the reduction of sodium in foods exist throughout Europe, many of which have succeeded in imposing new legislation and restrictions on manufacturers. CASH is claiming a reduction of 2.3 grams salt per day in the average British diet (currently 8.3 grams) would save 17,000 lives.
In Ireland for example, foods such as cereals have cut salt content by up to 60%.
Study details
Taking advantage of the hyper controlled conditions astronauts undertake on space missions, the MDCMM experimented by varying the salt levels in astronaut’s diets by up to double the recommended daily intake of 6 g.
On two different flight simulations, containing 105 and 205 prospective astronauts respectively, ten men were subjected to three separate daily salt levels – the recommended 6 grams, then 9 g and 12 g.
Those exposed to the highest level of salt per day showed high levels of water retention and took on less fluid through drinking.
"Nature has apparently found a way to conserve water that would otherwise be carried away into the urine by salt" experimental and clinical researcher at the MDCMM Dr. Friedrich C. Luft was quoted as saying.
Analysis on astronauts undergoing simulated flights to Mars showed that doubling the daily recommended salt intake of 6 grams (g) actually increased water levels within the body, suppressed thirst and increased hunger.
Luft explained the three core processes that reverse the traditional assumptions about salt’s dehydrating effect on the body:
“First, although salt intake may acutely promote immediate secondary drinking by local sensors, salt in parallel induces both body-water conservation and generation thereby surprisingly reducing overall fluid intake.
“Second, the process of salt elimination is characterized by water conservation and not by salt-driven water losses, as formerly believed.
“Third, the process of sodium elimination requires careful urea production and reabsorption to prevent otherwise salt-driven body-water losses.”
In other words, when high levels of salt are taken on, the body works to retain water in the kidneys whilst concentrating salt levels into the urine, and for this reason subjects drank less water when consuming salty diets.
Previous theories stipulated that salt binds to water molecules and transports them into urine, causing dehydration and increased thirst.
Source: Journal of Clinical Investigation
Published: doi.org/10.1172/JCI88530
'Increased salt consumption induces body water conservation and decreases fluid intake'
Authors: Friedrich C Luft et al.