Firstly, you don’t get flu,but you can experience a few flu-like symptoms as you restrict your carbohydrate intake. Reducing carbohydrate intake causes the kidneys to retain less salt, which is subsequently excreted in urine.
Salt is essential for life – amongst other things it helps maintain blood pressure, so a lack of salt can leave you feeling light headed, dizzy or even nauseous – especially when standing up after sitting or lying down for a period.
Because our foods are so full of salt these days we’ve kind of forgotten the value of it, but our ancestors knew only too well how important it was to survival. The English word salary comes from the latin salarium, which relates to the payment of salt given to Roman soldiers. Sayings relating to this tradition are still in use today – “He’s really worth his salt“, for example. I digress.
Personally I felt a little light headed after the first day or so, but this was easily corrected by increasing my salt intake to around 5g (5000mg) a day by drinking a couple of cups of Bovril, Miso soup or other clear broth. Normal salt intake on the standard western diet is around 3000mg, but on a low carb diet, around an extra 2g of sodium becomes necessary – and presents no risk in a healthy individual.
If sodium levels fall very much, then the adrenal gland secretes a hormone that causes the kidneys to use potassium to restrict sodium loss. This subsequent lack of potassium, if allowed to continue will also deplete magnesium, eventually leading to muscle cramps and cardiac dysrhythmias as our muscles struggle to function.
Therefore a good slow release magnesium supplement (if you have a history of kidney problems, discuss this with your physician), potassium supplements and a little more salt than normal are all that’s required to stave off any undesirable side effects of your adjustment in diet.
Going forward, deep leafy green are rich sources of magnesium, so broths and stews containing them are probably a more nutritious and enjoyable solution to popping pills. Lo Salt is also a good source of potassium, so consider switching from normal salt.