Sodium recommendations: Right for the wrong reasons?

Published 5.9.2017
People with high blood pressure or kidney problems get told to eat a low salt diet and to drink plenty of water to flush out excess. Gina Kolata in the New York Times reports on a study of astronauts that may upend medicine's understanding of how the body regulates sodium.

The article didn’t go where I thought it would, I expected Kolata to announce that a “low salt” diet was a fraud and the cause of obesity and sundry health problems. Instead, the article detailed the findings from experiments on Russian astronauts on long jaunts in space.

Sodium is one of those elements that the body tightly controls. Medicine has long thought that the amount of sodium in the body is dependent on the amount of fluid. The excretes excess sodium. The findings reported in the article contradict this. The astronauts drank less water when eating the (relatively) high salt diet, but still excreted more sodium. Their bodies had apparently generated the water necessary to rid the body of the excess salt.

The astronauts enjoyed the high salt diet more, but they were also more hungry while eating it. They didn’t care for the low salt version, but were more satiated by the same amount of food. The diets were gauged to maintain weight, this wasn’t a study of weight loss. I would guess that those who tout the food reward theory will find much of interest here. Certainly kidney specialists so.

But urine tests suggested another explanation. The crew members were increasing production of glucocorticoid hormones, which influence both metabolism and immune function.

This quote is an example of poor editing. Which urine tests? When salt intake was low, or when it was high? The article is not clear. In the previous paragraph the low salt diet was under discussion. However, based on the mouse study discussed in the next paragraph, the increased production occurred with the high salt diet.

The animals were getting water — but not by drinking it. The increased levels of glucocorticoid hormones broke down fat and muscle in their own bodies. This freed up water for the body to use.

But that process requires energy, Dr. 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 similar happens on a salty diet has come as a revelation.

One implication is that high salt diet could help break down fat— however, if a high fat diet makes you more hungry, then you’ve negated any advantage. In the end, whether high salt, low salt, high fat, low fat, high carb, low carb, it's the energy balance that matters. If eating a low carb high fat diet is satiating for you, doesn't cause you health issues and results in a caloric deficit, then you will lose weight. The exact same statement can be made for a High carb low fat diet. I didn't bother with high and low protein, because my observation that the range of protein intake is much narrower. Nobody eats a diet of 80% protein, but there are people who eat diets of 80% carbs or 80% fat— to note the extremes.

Other reasons not to pile on the salt:

And, Dr. Titze said, high glucocorticoid levels are linked to such conditions as osteoporosis, muscle loss, Type 2 diabetes and other metabolic problems.

They are not ready to say that salt is unrelated to high blood pressure either, but it could be that they are right for the wrong reasons. Sodium ions are opposite calcium (Ca) ions in many bodily functions, so the fact that excess sodium would influence Ca in the body does not surprise me.

Nothing in this article changes my view or approach to salt, especially given the link to osteoporosis— a topic worth some research on my part. My opinion is that most of the salt in diets (at least in the US) is the result of munching on ultra-processed foods. As I cook 80%+ of my food myself from non-ultra-processed ingredients, I control the amount of salt in my food. I don't fear salt and do use it in my cooking, but I have no need to add the levels necessary to maintain flavor in factory processed products.