Two excellent recent studies from Germany and Vanderbilt University in Tennessee tell us that us excess salt:
• causes hunger, rather than thirst
• breaks down muscle and fat
• may be a primary dietary factor in the high rates of obesity, diabetes, heart attacks and strokes in North America because it raises blood levels of adrenal hormones (cortisol) (Journal of Clinical Investigation, April 17, 2017).
The common belief is that increasing salt intake increases urination and the more you urinate, the more fluid you have to drink to replace the fluid that you have lost. However, in 2011, these researchers studied Russian cosmonauts in a human space flight simulation program in Moscow, and were astonished to find that the cosmonauts actually drank less water when their daily salt intake was doubled (from 6 to 12 grams per day). Their follow-up studies, published last month, show that:
• The reason that extra salt decreases thirst and causes you to drink less fluid is that extra salt breaks down the muscles and fat in your body and these calories are used to supply energy for your body.
• Converting muscles and fat in your body to energy produces tremendous amounts of water because the end products of the chemical reactions that produce energy for your body are calories, water and carbon dioxide. The more body muscle and fat you break down, the more water is produced by your body and the less fluid you need to drink.
• When you take more salt than your body needs, your body responds to the loss of muscle and fat by needing extra calories to replace those that are lost, so extra salt makes you hungry and you eat more food. The researchers propose that the extra food you eat because of excess salt can cause you to gain weight and increase risk for diabetes, heart attacks and strokes. The breakdown of muscle caused by excess salt may also increase risk for sports injuries.
Explanation of the Mechanism The authors showed that extra salt stimulates your adrenal glands to increase your body's production of glucocorticoids (cortisol, cortisone, etc.) that break down muscle protein that your liver uses to make and release urea into the bloodstream. Urea helps to retain the water that you lose through your kidneys from taking in extra salt. The glutocorticoids can also raise blood sugar, make you hungry, weaken bones and form plaques in arteries. This research was meticulously designed, published in a very prestigious medical research journal and done by 21 authors. However, further studies are needed to confirm their findings and the amounts of salt that may be associated with increased risk for obesity, diabetes, heart attacks and so forth.
My Recommendations While we await further data, I recommend that you continue to follow the heart-healthy diet that I have recommended for many years. This way of eating is relatively low in salt because you eat lots of plants and fresh foods that have not been altered by food manufacturers. See Who Should Restrict Salt and Heart-Healthy Diet: New Studies
• Base your diet on fresh fruits, vegetables, whole (un-ground) grains, beans, nuts and other seeds.
• Restrict processed foods that often have added salt (and sugar).
• Don't add a lot of salt to your food unless your doctor has advised you that you need extra salt. Some medications or medical conditions can cause excessive loss of salt. See Salt Intake Can Be Too High or Too Low
• Sometimes you need to take extra salt, such as when you exercise for more than three hours in hot weather, drink too much water especially during exercise, are dehydrated or have severe vomiting or diarrhea. Symptoms of salt deficiency include weakness, fatigue, headache, nausea and vomiting, muscle cramps or spasms, confusion and irritability. Check with your doctor, who can draw blood tests for sodium, chloride and potassium.
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