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Everything you know about salt and your health may be wrong

A new book claims the salt shaker is not an enemy — far from it — most of us don’t need to watch our salt intake at all and, in fact, might be better off consuming more than less of it.

• Peta Bee
• The Times
• 4:34PM May 16, 2017
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We are warned that salty diets raise our blood pressure and our risk of diseases, from stomach cancer and osteoporosis to kidney disease and vascular dementia, that too much of the white stuff can exacerbate symptoms of asthma and diabetes. Why wouldn’t we want to cut down? Yet researchers are beginning to pick apart the science that suggests salt is bad for us, proposing that much of what we thought we knew about salt is wrong, and that the salt cellar may even hold the key to weight loss.

Salt — sodium chloride — is essential for health, needed by every cell in the body and required to regulate fluid balance as well as for nerves and muscles (including those in the heart) to function well. While too much salt has a negative influence on health, a growing number of people think so does too little.

Next month comes a highly controversial book by a respected US cardiovascular research scientist, who is also an associate editor of the British Medical Journal’s Open Heart, a journal published in partnership with the British Cardiovascular Society. In The Salt Fix: Why the Experts Got It All Wrong and How Eating More Might Save Your Life, Dr James DiNicolantonio argues that the salt shaker is not an enemy — far from it. According to the online publicity for the book, most of us don’t need to watch our salt intake at all and, in fact, might be better off consuming more salt than less of it.

 

Added to that are two hefty studies published in the most recent issue of the Journal of Clinical Investigation, which are the latest to contradict existing evidence about salt, going so far as to question conventional wisdom that salt makes us thirsty. Both new trials were led by Jens Titze, a kidney specialist and associate professor of medicine and of molecular physiology and biophysics at Vanderbilt University Medical Centre in Nashville, Tennessee. In the first of the investigations, his unusual group of subjects — 10 Russian astronauts studied during two simulated space flights to Mars lasting 105 and 205 days — were asked to stick to a diet of varying degrees of saltiness. On the shorter of the two flights, the crew ate a diet containing 12g of salt, double the level recommended as a healthy upper limit for adults in the UK, followed by 28-day cycles of 9g daily salt and then a low-salt diet of 6g a day. They were given a similar intake on the longer flight, but with another 28-day cycle of 12g of daily salt added to the schedule.

Any medical textbook will explain how and why salt makes you thirsty, that the more salt you consume in food, the greater the urge to drink as your body attempts to maintain its delicate concentrations of sodium in the blood. It’s crucial for health that these levels are carefully controlled, which is why excess salt is eventually excreted in urine. Initially, Titze observed that to be the case. As salt intake in their diet rose, so the astronauts’ urine volume increased as they excreted it, ensuring the amount of sodium in their blood remained the same. Yet, when he looked at their fluid intake, Titze found an unexpected anomaly. The saltier their diet, the less thirsty they had become and the less they drank. How was this possible? The only feasible explanation, says Titze, is that their bodies produced more water in response to the salty food.

Professor Graham MacGregor, the chairman of the group Consensus Action on Salt and Health, which campaigns for the food industry to cut down on salt in processed foods, says he’s “deeply sceptical” about the findings. “There’s a clear physiological basis for salt making us thirsty, but it’s also evident in practical terms,” he says. “We’ve all experienced the sensation of thirst that comes with eating the dishes of salty nuts and the crisps placed on bars by publicans wanting us to drink more.”

Even more of a mystery to Titze was the astronauts complaining that they were hungrier when eating the diet with most salt, despite their controlled and consistent calorie intake. Tests of their urine samples revealed the subjects were producing higher levels of glucocorticoid hormones, known to influence immune function, but also metabolism. Titze carried out a subsequent experiment using laboratory mice. He found the same effect in the animals, but also gained a better understanding of what was going on. Raised levels of hormones triggered the body to break down fat and muscle, freeing excess water for the body to use. The whole process used up energy and, in short, the more salt the mice ate, the more calories they burnt. So pronounced was the effect that the mice gobbled 25 per cent more food just to maintain their body weight when on the saltiest diet.

Titze says he was certainly “surprised” by the results. “I could never have imagined that salt intake might have such a dramatic impact on energy metabolism,” he says. “We had always focused on blood pressure in research. That was the only thing we could think of that it might affect.”

Pass the salt shaker.

In The Salt Fix, DiNicolantonio claims that too little salt in the diet can lead to cravings for sugar and refined carbs and, ultimately, to weight gain.

Does all of this mean the unthinkable — that eating salt could be the answer to our dieting woes?

In theory, yes, but not so fast, Titze says. “Many people are now asking whether it might be a good idea to increase salt intake to lose weight on a diet,” he says. “I think it is not a good idea, for several reasons. Firstly, hunger is a very significant reason to flunk a weight reduction program - and salt seems to make us hungry. Secondly, even if successful, what would the weight reduction look like? Glucocorticoids reduce muscle mass, and increase the relative amount of fat. I’m not sure that this is the toned, lean weight loss people are dreaming of.”

What’s more, he says, elevated levels of glucocorticoid hormones that seem to accompany a salty diet could contribute to the development of some chronic diseases. “These hormones are associated with increased risk of stroke and cardiovascular disease,” Titze says. “Not good.” His studies are a starting point and follow-up research might trigger researchers to “rethink the principles of salt metabolism”, he says, but for the foreseeable future, at least, the message is still to refrain from too much salt.

Last year Public Health England revealed that adults cut their average salt consumption by 0.9g a day in the decade from 2005 to 2014 and that, overall, salt intake has dropped by 11 per cent in ten years largely due to manufacturers adding less sodium to food. The average person in the UK is thought to eat about 8.1g salt a day.

MacGregor thinks that’s still too much. Most people, he says, are eating a third more than the maximum recommended intake - less than 1g a day for babies rising to 6g a day (roughly one teaspoon) for anybody 11 years and over. “There are occasionally contradictory findings, but experts from the World Health Organisation, the American Heart Association, Public Health England and ourselves have reviewed all of the evidence and reached the same conclusion,” he says. Too much salt is bad for you.”

The Times

http://www.theaustralian.com.au/news/world/the-times/everything-you-know-about-salt-and-your-health-may-be-wrong/news-story/31be5790ca02ba932f47fe9934640874