Author: Théophile Niyitegeka

{New studies show that salty food diminishes thirst while increasing hunger, due to a higher need for energy}

We’ve all heard it: eating salty foods makes you thirstier. But what sounds like good nutritional advice turns out to be an old-wives’ tale. In a study carried out during a simulated mission to Mars, an international group of scientists has found exactly the opposite to be true. “Cosmonauts” who ate more salt retained more water, weren’t as thirsty, and needed more energy.

For some reason, no one had ever carried out a long-term study to determine the relationship between the amount of salt in a person’s diet and his drinking habits. Scientists have known that increasing a person’s salt intake stimulates the production of more urine — it has simply been assumed that the extra fluid comes from drinking. Not so fast! say researchers from the German Aerospace Center (DLR), the Max Delbrück Center for Molecular Medicine (MDC), Vanderbilt University and colleagues around the world. Recently they took advantage of a simulated mission to Mars to put the old adage to the test. Their conclusions appear in two papers in the current issue of The Journal of Clinical Investigation.

What does salt have to do with Mars? Nothing, really, except that on a long space voyage conserving every drop of water might be crucial. A connection between salt intake and drinking could affect your calculations — you wouldn’t want an interplanetary traveler to die because he liked an occasional pinch of salt on his food. The real interest in the simulation, however, was that it provided an environment in which every aspect of a person’s nutrition, water consumption, and salt intake could be controlled and measured.

The studies were carried out by Natalia Rakova (MD, PhD) of the Charité and MDC and her colleagues. The subjects were two groups of 10 male volunteers sealed into a mock spaceship for two simulated flights to Mars. The first group was examined for 105 days; the second over 205 days. They had identical diets except that over periods lasting several weeks, they were given three different levels of salt in their food.

The results confirmed that eating more salt led to a higher salt content in urine — no surprise there. Nor was there any surprise in a correlation between amounts of salt and overall quantity of urine. But the increase wasn’t due to more drinking — in fact, a salty diet caused the subjects to drink less. Salt was triggering a mechanism to conserve water in the kidneys.

Before the study, the prevailing hypothesis had been that the charged sodium and chloride ions in salt grabbed onto water molecules and dragged them into the urine. The new results showed something different: salt stayed in the urine, while water moved back into the kidney and body. This was completely puzzling to Prof. Jens Titze, MD of the University of Erlangen and Vanderbilt University Medical Center and his colleagues. “What alternative driving force could make water move back?” Titze asked.

Experiments in mice hinted that urea might be involved. This substance is formed in muscles and the liver as a way of shedding nitrogen. In mice, urea was accumulating in the kidney, where it counteracts the water-drawing force of sodium and chloride. But synthesizing urea takes a lot of energy, which explains why mice on a high-salt diet were eating more. Higher salt didn’t increase their thirst, but it did make them hungrier. Also the human “cosmonauts” receiving a salty diet complained about being hungry.

The project revises scientists’ view of the function of urea in our bodies. “It’s not solely a waste product, as has been assumed,” Prof. Friedrich C. Luft, MD of the Charité and MDC says. “Instead, it turns out to be a very important osmolyte — a compound that binds to water and helps transport it. Its function is to keep water in when our bodies get rid of salt. Nature has apparently found a way to conserve water that would otherwise be carried away into the urine by salt.”

The new findings change the way scientists have thought about the process by which the body achieves water homeostasis — maintaining a proper amount and balance. That must happen whether a body is being sent to Mars or not. “We now have to see this process as a concerted activity of the liver, muscle and kidney,” says Jens Titze.

“While we didn’t directly address blood pressure and other aspects of the cardiovascular system, it’s also clear that their functions are tightly connected to water homeostasis and energy metabolism.”

Source:Science Daily

{A new study from the Icahn School of Medicine at Mount Sinai provides important insights into how the body regulates its production of heat, a process known as thermogenesis that is currently intensely studied as a target of diabetes and obesity treatment in humans.}

While researchers had previously hypothesized that macrophages, a class of white blood cells, played a major role in thermogenesis, the new study suggests that the main driver of thermogenesis is the sympathetic nervous system, which is chiefly controlled by the brain. The results were published online in Nature Medicine.

The Mount Sinai research team led by Christoph Buettner, MD, PhD, senior author of the study and Professor of Medicine (Endocrinology, Diabetes, and Bone Disease) at the Icahn School of Medicine at Mount Sinai, focused on catecholamines, hormones released by the sympathetic nervous system to activate brown fat tissue. Brown adipose tissue is a type of fat tissue that burns energy to produce heat and keep us warm. Catecholamines can also convert white fat tissue, the more familiar kind of fat tissue that stores lipids, into a tissue that resembles brown fat. The researchers tested whether macrophages could provide an alternative source of catecholamines, as had been proposed in recent years.

“Thermogenesis is a metabolic process that receives a lot of interest as a target of drugs that allow you to burn energy and hence reduce obesity and improve diabetes. It turns out that macrophages are not that important, as they are unable to make catecholamines, but clearly the brain through the sympathetic nervous system is,” says Dr. Buettner. “Therefore, it is very important to study the role of the brain and the sympathetic nervous system when it comes to understanding metabolism.”

The ability to generate heat is critical for the survival of warm-blooded animals, including humans, as it prevents death by hypothermia. “This evolutionary pressure shaped the biology of humans and that of other warm-blooded animals, and may in part explain why humans are susceptible to developing diabetes in the environment in which we live,” says Dr. Buettner.

According to Dr. Buettner, while a lot of effort has been invested in targeting the immune system to cure diabetes and insulin resistance, as of yet there are no anti-inflammatory drugs that have been shown to work well in humans with metabolic disease. “Our study suggests that perhaps the key to combating the devastating effects of diabetes and obesity in humans is to restore the control of thermogenesis and metabolism by the brain and the autonomic nervous system,” says Dr. Buettner.

Source:Science Daily