Table salt(Sodium chloride) seems like such an insignificant thing since it is so plentiful, but it has a large impact on your health and the way you function given it is the primary source of sodium in the diet. In fact, without sodium you would not be. Sodium is important for fluid balance, electrical activity/nerve conduction, and the movement of other ions in to or out of our cells. When sodium gets too low, it can cause major problems, particularly the ones mentioned above. These repercussions are not solely due to a Paleo Diet, they are standard in all low carbohydrate diets. While the Paleo Diet is not a low carbohydrate diet, it is typically much lower in carbohydrate than what most people are accustomed to eating since processed foods are eschewed.
When a person begins a low carbohydrate diet, they experience something known as the natriuresis of fasting. Natriuresis is the excretion of sodium via the urine due to the action of natriuretic peptides on the kidneys. Since water follows sodium, this also causes dumping of water via the urine. Most people, in general, attempt to limit their sodium intake because that is what's recommended to them in the popular press. While there may be a small portion of the population that is very sensitive to salt intake from a blood pressure standpoint, a low carbohydrate diet more or less removes that issue as the loss of sodium and water will obviously lower blood pressure. Even if you aren't someone who tries to keep their sodium intake low, beginning any sort of low carbohydrate diet will increase your sodium requirements as your body flushes it out. While the Paleo Diet does not have to be a low carbohydrate diet per say, most people will dramatically reduce their carbohydrate intake when they reduce or eliminate processed foods as they switch from a Standard American Diet to a Paleo Diet. Let's take a look at the negative effects associated with this problem.
Dizziness/fatigue problems on the Paleo dietWhile most people have a short adjustment phase when implementing the Paleo diet, people who implement it without increasing their salt intake can run in to dizziness or fatigue problems. There are a couple of reasons that this can occur. For one, the dizziness typically comes from low blood pressure. When moving quickly from a seated or lying position to standing, your body doesn't increase blood pressure quickly enough so it takes a little longer and a little more effort for the blood to make it to your brain. Many people mistake this for low blood glucose but it's remedied quite easily with a higher salt intake.
The lack of energy can be attributed to a couple of things. For one, salt helps many other substances enter your cells because it follows an electrochemical gradient. Salt always goes from high concentration to low concentration, so your cells actively take it in because their sodium levels tend to be lower than the blood. This electrochemical gradient also helps pull other substances such as iodine, glucose, and calcium in to or out of the cell depending on what type of transporter you are dealing with and the concentration of sodium inside and outside of the cell. When sodium levels drop, this leaves less sodium to move these nutrients in to cells which can negatively impact energy levels. This is an important phenomenon, particularly with calcium and iodine.
The Sodium/Calcium Exchanger (NCX)Muscular contraction is accomplished by moving calcium from an area of the cell called the sarcoplasmic reticulum in to the cytosol via calcium channels. The muscle relaxes once the calcium moves back in to the sarcoplasmic reticulum. In skeletal, cardiac and smooth muscle cells; calcium is pumped back in to the sarcoplasmic reticulum via the sodium/calcium exchanger (NCX) and Calcium ATPase pump. The NCX is important because it uses no energy and can move large amounts of calcium quickly via the electrochemical gradient of sodium by moving 3 molecules of sodium in one direction and one molecule of calcium in the other. Think of it like a child who wants to enter a building that is too weak to move the revolving door. In order for that child to enter the door, they wait for someone strong enough to move the door to leave the building. As that person exits, the child moves in to the door and allows the other person to power it. The Calcium ATPase pump works in concert with the NCX but can only move small amounts of calcium and requires ATP (Energy) to power the process. If there is not enough sodium to power the NCX, this means the Calcium ATPase pump must move all of the calcium and use up a lot of energy to do so. This may be the primary reason fatigue creeps in during a low carb diet. Increasing salt intake typically remedies the situation.
Coincidentally, this also appears to be why people tend to become constipated on a low carbohydrate diet. The NCX is highly expressed in smooth muscle, particularly the smooth muscle cells that line your intestines. Not having enough salt to move calcium quickly may be one of the primary reasons many people become constipated or experience sluggish bowel movements on a low carb diet. Increasing salt intake almost always fixes both of these problems.
One interesting note on the NCX is that it is also highly expressed in the adrenal glands. Chromaffin cells, cells of the adrenal gland that secrete the stress hormones epinepherine(Adrenaline) and norepinepherine(Noradrenaline) in response to stress, show high levels of expression of the NCX. When the NCX of these cells is inhibited, they secrete more of these hormones because the same movement of calcium that causes muscular contraction also causes hormone secretion(1). When the NCX is inhibited, it takes longer to move calcium back in to the endoplasmic reticulum of these cells which increases the length of time these cells secrete hormones. This could have implications in adrenal fatigue as the same NCX is found in the zona fasciculata of the adrenal gland which is responsible for secreting cortisol(2). One of the hallmarks of adrenal fatigue is an inability to regulate electrolyte balance because aldosterone, the chief mineralocorticoid responsible for electrolyte balance via salt retention and potassium excretion, gets too low and salt is wasted via the urine. Perhaps in the beginning stages of adrenal fatigue, aldosterone gets too low and cortisol is oversecreted because the NCX does not have enough salt to move calcium quickly. This could cause cortisol to be secreted for longer periods of time and inhibit the hypothalamus from sending the signal to secrete more aldosterone. Only a working hypothesis but interesting nonetheless.
The Sodium Iodide Symporter (NIS)The sodium iodide symporter (NIS) moves 1 iodide and 2 sodium ions in the same direction and is the first step in moving iodine in to the thyroid gland to make thyroid hormones. In this blog we will use iodine and iodide interchangeably, in the future one on iodine we will differentiate between the two. The thyroid hormones T4 and T3 have four and three molecules of iodine contained within them, respectively. Given that nearly every one of your cells is dependent on T3 to regulate it's metabolism (aka energy production), thyroid hormone is pretty important for proper function and low thyroid can certainly negatively impact energy levels. Without iodine, there are no thyroid hormones. Without sufficient sodium to move the iodine in to the thyroid gland, there are no thyroid hormones. The salt wasting that typically happens as a result of a low carbohydrate diet may slow down iodine uptake by the thyroid by inhibiting the NIS. This could be the mechanism by which going very low carbohydrate for too long can negatively impact thyroid function and could also contribute to the fatigue associated with low carbohydrate diets. Again, a Paleo diet does not have to be low carb, but since it is lower carb than what most people tend to eat; increasing salt is a good idea.
ConclusionSalt is your friend on the Paleo diet or any lower carbohydrate diet for that matter. Looking at studies that examine the use of salt in the Standard American Diet can be deceiving because most people don't realize that these studies don't apply if you are eating a lower amount of carbohydrate than what is typical. Since decreasing carbohydrate intake leads to wasting of sodium from the urine, the salt requirement for people who undertake a Paleo Diet increases. Many of the unwelcome changes a person notices when switching to this type of diet; including fatigue, constipation, and dizziness and headache associate with low blood pressure; can be alleviated by increasing salt intake. Most people consciously avoid salt because they have been told to by the popular press. A person who avoids salt and begins a Paleo Diet may be in for a rocky road unless they increase their salt intake to help maintain blood pressure, help regulate fluid balance, and provide sodium to help power some of the transporters that help other nutrients enter your cells.
For more on the intricacies of low and lower carbohydrate diets, check out The Art and Science of Low Carbohydrate Diets.