I was keen to understand why all the low-carb diet resources tell you to eat more salt. I therefore decided to look into this in greater detail. The problem I encountered was that nothing actually states the reasoning behind it; sources merely allude to the requirements, then make recommendations on how to achieve them.
What I was keen to understand in particular, is the role of insulin in causing the kidneys to retain salt. The below is what I’ve managed to piece together.
As always, I must state that I have no medical or dietary training; all I can do is try and present the results of my own reading in as clear and jargon-free way as possible. If readers’ comments can help guide my understanding, then all feedback will be gratefully received!
So here goes… Salt!
When you switch over to a ketogenic diet, you’re effectively changing the way your body creates and burns energy.
On a glucose-based metabolism, the energy-form ‘glycogen’ is produced in the liver. This energy is water-soluble and transported around the body in your blood. The blood-stream is therefore our ‘road-network’ for distributing energy to all the cells and muscles that need it. Glycogen is also stored in the muscles, so the blood-motorway serves to ‘top up’ these stores when required.
Because glycogen is transported in liquid & is water-soluble; it’s unsurprising that glycogen itself contains a lot of water. In fact, it’s stored in liquid form; three to four parts water to one part glycogen (sources state 3-4g water to 1g glycogen).
When you restrict carbohydrate, you stop consuming glucose, the raw-material from which glycogen is made (see Fuel versus Energy for more details). Your stores of glycogen therefore deplete as your body burns energy, and because glycogen carries 3-4 parts water; your body loses a heck of a lot of liquid with it! This is the reason why weight-loss is often rapid at the start of a LCHF diet. You’re shipping the water stored alongside glycogen; and water is quite heavy!
What’s this got to do with salt?
We’ve identified that depleting glycogen stores also ships water. How is that water excreted? Predominantly in your urine.
Salt is vital to the body for survival; so important in fact that your tongue has special ‘salt-sensors’ in it, to detect its taste and prompt you to add more if levels are insufficient. If something is especially salty, your body prompts you to drink. This is why many pubs offer salty snacks such as peanuts or crisps – they want you to drink more! A high concentration of electrolytes in the body triggers our thirst mechanism – salt is an electrolyte!
So in entering a state of ketosis, your body is excreting water and salt through the depletion of glycogen. If high salt-levels trigger the thirst mechanism, but salt-levels are going down (as is water); it naturally follows that the thirst-mechanism is not sufficiently triggered to cover this water-loss. Our body’s water-balance gets temporarily thrown out of sync and we become dehydrated. This combination of mineral-deficiency and dehydration can leave you feeling incredibly nauseous, tired, weak and highly prone to headaches.
There is something else to throw into the mix – insulin.
This is a very difficult thing for a lay-person to research. The science is prohibitively complex and the information tends not to deal directly with this subject; rather simply referring to it as an aside.
One of the lesser known functions of insulin is to signal salt-retention in the kidneys. When you eat carbohydrate, your insulin levels rise. The insulin then tells your kidneys to retain salt and not excrete it. By eating carbohydrate, we’re not only getting fatter, but the salt we eat is not being released by the body, which then has adverse effects on blood-pressure. A low-salt diet can also lead to insulin-resistance, the precursor to type-2 diabetes (your body no longer responds to the insulin you produce).
Conversely, when you cut carbs; your insulin-levels decrease, which then tells your kidneys to release salt. The healthy ‘salt-cycle’ is restored and the body slowly adjusts to its normal, natural pattern.
In addition to water-loss through glycogen-depletion; insulin-reduction tells your kidneys to release salt from the body. For these two reasons, it’s important to up your salt in-take when first adopting a ketogenic-diet.
To prevent dehydration and the above symptoms (sometimes termed ‘keto-flu’), remember to drink lots of water and top your sodium levels up by drinking bouillon (stock cubes in water) and adding sufficient salt to your meals to cover the loss.
That way, your changeover to a healthy keto-plan will be a happy and safe one. Enjoy the journey!
I hope this helps and thanks for reading,