Electrolytes, Fatigue and Brain Fog: What Your Body Is Actually Trying to Tell You

Electrolytes have had a bit of a wellness moment lately, mostly in the form of pastel-coloured sachets marketed at gym-goers. But the reality of what electrolytes do in the body, and what happens when they go wrong, is so much more interesting and clinically important than the marketing suggests. Here’s the real science.

What electrolytes actually are

Electrolytes are minerals that carry an electrical charge when dissolved in water. They are essential, meaning you must consume them because your body cannot make them from scratch. With the exception of bicarbonate, all electrolytes are minerals. Sodium, potassium, chloride, calcium, magnesium, and phosphate are the main players.

Here is what makes them so fundamental: they maintain the fluid balance inside and outside your cells, they regulate blood pH (which must stay within a very narrow range of 7.35 to 7.45), and they create the electrical gradients that allow your neurons to fire, your muscles to contract, and your heart to beat.

The sodium-potassium pump is perhaps the best illustration of this. Every cell in your body runs a constant pump that moves three sodium ions out for every two potassium ions in, maintaining the electrical gradient that makes nerve conduction and muscle contraction possible. This pump uses roughly 40% of your body's resting energy expenditure. An underactive thyroid slows this pump down, which is one reason hypothyroidism can cause such pervasive fatigue and sluggishness.

Sodium: far more than a seasoning

Your body contains about 105g of sodium in total, though only about 15g of that is in the blood where we can measure it. Sodium is the master electrolyte of the extracellular space, the fluid outside your cells.

Contrary to what most people assume, serum sodium levels are not simply a reflection of how much salt you eat. They reflect your metabolic state, your hydration, and the activity of your adrenal glands. Specifically, the RAAS system (renin-angiotensin-aldosterone system) regulates sodium and fluid balance with remarkable precision. When blood volume drops, the kidneys trigger a cascade that ultimately tells the body to hold onto sodium and water. The adrenals release aldosterone to drive this process.

When the HPA axis (hypothalamic-pituitary-adrenal axis) is dysregulated, as it so often is in women under chronic stress, this aldosterone response can become impaired. The body struggles to hold onto sodium, and you start to see low sodium on blood tests alongside symptoms like constant thirst, frequent urination, fatigue, brain fog, and light-headedness. The extreme of this picture is Addison's disease, but subclinical adrenal dysregulation is something I see regularly.

Potassium: the intracellular partner

Potassium is the dominant mineral inside your cells, around 30 times more concentrated inside than outside. Because of this, the serum reading we get from a blood test represents less than 1% of your total body potassium, which means it can appear normal in the blood even when your cellular stores are low.

Potassium moves in the opposite direction to sodium. When your body is retaining sodium, potassium is excreted in the urine. Insulin, stress hormones, and metabolic acidosis all shift potassium around, which is why it's such a useful clinical clue when read carefully alongside other markers.

The most common reason I see low potassium in clinic is chronic diarrhoea or IBS with a diarrhoeal pattern. Significant fluid losses through the gut deplete potassium aggressively, and it almost always needs active repletion, not just a banana or two.

Bicarbonate: the acid-base story no one talks about

This is the marker that I think deserves far more attention than it gets. Bicarbonate (HCO3) is the body's primary buffer against metabolic acid. And here is the uncomfortable truth: modern Western life, with its processed food, chronic stress, sedentary patterns, and poor sleep, places a significant acid burden on the body, often beyond what our kidneys and lungs can comfortably buffer.

The result is what's sometimes called chronic mild metabolic acidosis. It's not the dramatic acidosis you'd see in a medical emergency. Blood pH stays technically within range, because the body mobilises calcium and magnesium from bone, excretes more nitrogen, and puts the adrenals under strain trying to compensate. But over time, this quiet acid burden contributes to impaired parathyroid function, low vitamin D, bone loss, increased pain perception, kidney stress, and insulin resistance.

On a blood test, I look for a bicarbonate reading above 26 as optimal. Below that, the body is working harder to buffer. As it drops further, potassium starts to be pushed out of cells as a compensatory mechanism, and you begin to see elevated serum potassium as a late sign.

What happens when electrolytes are lost

Different types of loss create different electrolyte signatures, and understanding this helps enormously in clinic.

Significant diarrhoea from conditions like IBD, SIBO, laxative overuse, or post-gallbladder removal depletes sodium, potassium, chloride, and bicarbonate. Potassium loss is particularly severe and needs urgent attention alongside stopping the underlying leak.

Vomiting, whether from severe reflux, bulimia, cyclic vomiting syndrome, or hyperemesis in pregnancy, causes low sodium, very low potassium, and a significant drop in chloride (as stomach acid is lost). Bicarbonate rises in response, as the body tries to compensate for the loss of hydrogen ions.

Sweat losses from hot yoga, saunas, or intense exercise primarily take sodium and chloride. Potassium isn't lost significantly through sweat. The problem arises when people replenish sweat with plain water, which dilutes serum sodium further.

A note on electrolyte supplements

When I'm recommending an electrolyte supplement for a client with chronic diarrhoea, I'm looking for something with a high potassium content (200 to 400mg per serving), in a 2:1 or 3:1 potassium-to-sodium ratio, with some magnesium (as malate rather than citrate or oxide, which can worsen diarrhoea), and some chloride for acid-base support. For the athlete losing sodium through sweat, the ratio flips entirely and we want sodium at the front.

The formulation matters. This is not a one-product-fits-all situation.

The bigger picture

Electrolytes are not a wellness trend. They are fundamental to how your body works at a cellular level. When they're off, the consequences ripple through your energy, your nervous system, your cardiovascular function, and your hormones.

If you're struggling with persistent fatigue, muscle cramps, brain fog, or frequent urination that no one seems to have a clear answer for, electrolyte status and acid-base balance are absolutely worth exploring.

Book a consultation and let's look at the full picture together.