By Gina Kolata
he salt equation taught
to doctors for more than
200 years is not hard to
The body relies on
this essential mineral for
a variety of functions, including
blood pressure and the transmis-
sion of nerve impulses. Sodium
levels in the blood must be care-
If you eat a lot of salt — sodium chloride — you will become
thirsty and drink water, diluting
your blood enough to maintain
the proper concentration of sodium. Ultimately you will excrete
much of the excess salt and
water in urine.
The theory is intuitive and
simple. And it may be completely
New studies of Russian cosmonauts, held in isolation to
simulate space travel, show that
eating more salt made them less
thirsty but somehow hungrier.
Subsequent experiments found
that mice burned more calories
when they got more salt, eating
25 percent more just to maintain
The research, published
recently in two dense papers in
The Journal of Clinical
Investigation, contradicts much
of the conventional wisdom
about how the body handles salt
and suggests that high levels may
play a role in weight loss.
The findings have stunned
kidney specialists.“This is just
very novel and fascinating,” said
Dr. Melanie Hoenig, an assistant
professor of medicine at Harvard
Medical School. “The work was
Dr. James R. Johnston, a pro-
fessor at the University of
Pittsburgh, marked each unex-
pected finding in the margins of
the two papers. The studies were
covered with scribbles by the
time he was done.
“Really cool,” he said,
although he added that the findings need to be replicated.
The new studies are the culmination of a decadeslong quest by
a determined scientist, Dr. Jens
Titze, now a kidney specialist at
Vanderbilt University Medical
Center and the Interdisciplinary
Center for Clinical Research in
In 1991, as a medical student
in Berlin, he took a class on
human physiology in extreme
environments. The professor
who taught the course worked
with the European space program and presented data from a
simulated 28-day mission in
which a crew lived in a small capsule. The main goal was to learn
how the crew members would
get along. But the scientists also
had collected the astronauts’
urine and other physiological
Titze noticed something puz-
zling in the crew members’ data:
Their urine volumes went up and
down in a seven-day cycle. That
contradicted all he’d been taught
in medical school: There should
be no such temporal cycle.
In 1994, the Russian space
program decided to do a 135-day
simulation of life on the Mir
space station. Titze arranged to
go to Russia to study urine patterns among the crew members
and how these were affected by
salt in the diet.
A striking finding emerged: a
28-day rhythm in the amount of
sodium the cosmonauts’ bodies
retained that was not linked to
the amount of urine they produced. And the sodium rhythms
were much more pronounced
than the urine patterns.
The sodium levels should
have been rising and falling with
the volume of urine. Although
the study wasn’t perfect — the
crew members’ sodium intake
was not precisely calibrated —
Titze was convinced something
other than fluid intake was influencing sodium stores in the
The conclusion, he realized,
In 2006, the Russian space
program announced two more
simulation studies, one lasting
105 days and the other 520 days.
Titze saw a chance to figure out
whether his anomalous findings
In the shorter simulation, the
cosmonauts ate a diet containing
12 grams of salt daily, followed
by 9 grams daily, and then a low-salt diet of 6 grams daily, each for
a 28-day period. In the longer
mission, the cosmonauts also ate
an additional cycle of 12 grams of
Like most of us, the cosmonauts liked their salt. Oliver
Knickel, 33, a German citizen participating in the program who is
now an automotive engineer in
Stuttgart, recalled that even the
food that supplied 12 grams a day
was not salty enough for him.
When the salt level got down
to 6 grams, he said, “It didn’t
The real shocker came when
Titze measured the amount of
sodium excreted in the crew’s
urine, the volume of their urine,
and the amount of sodium in
The mysterious patterns in
urine volume persisted, but
everything seemed to proceed
according to the textbooks.
When the crew ate more salt,
they excreted more salt; the
amount of sodium in their blood
remained constant, and their
urine volume increased.
“But then we had a look at
fluid intake, and were more than
surprised,” he said.
Instead of drinking more, the
crew were drinking less in the
long run when getting more salt.
So where was the excreted water
“There was only one way to
explain this phenomenon,” Titze
said. “The body most likely had
generated or produced water
when salt intake was high.”
To get further insight, Titze
began a study of mice in the lab-
oratory. Sure enough, the more
salt he added to the animals’
diet, the less water they drank.
And he saw why.
The animals were getting
water — but not by drinking it.
The increased levels of glucocor-
ticoid hormones broke down fat
and muscle in their own bodies.
This freed up water for the body
to use. But that process requires
energy, Titze also found, which is
why the mice ate 25 percent
more food on a high-salt diet.
The hormones also may be a
cause of the strange long-term
fluctuations in urine volume.
Scientists knew that a starving
body will burn its own fat and
muscle for sustenance. But the
realization that something simi-
lar happens on a salty diet has
come as a revelation.
People do what camels do,
noted Dr. Mark Zeidel, a nephrol-
ogist at Harvard Medical School
who wrote an editorial accompa-
nying Titze’s studies. A camel
traveling through the desert that
has no water to drink gets water
instead by breaking down the fat
in its hump. One of the many
implications of this finding is
that salt may be involved in
weight loss. Generally, scientists
have assumed that a high-salt
diet encourages a greater intake
of fluids, which increases weight.
But if balancing a higher salt
intake requires the body to break
down tissue, it may also increase
Still, Titze said he would not
advise eating a lot of salt to lose
weight. If his results are correct,
more salt will make you hungrier
in the long run, so you would
have to be sure you did not eat
more food to make up for the
extra calories burned.
And, Titze said, high glucocor-ticoid levels are linked to such
conditions as osteoporosis, muscle loss, Type 2 diabetes and
other metabolic problems.
— The New York Times
we know about salt
may be wrong
An undated handout
photo of the Mars500
crew of cosmonauts
inside the isolation
facility in Moscow.
INDIA ABROAD June 23, 2017 51 CUISINE