Electrolytes: Sodium, Potassium & Magnesium

When people dramatically cut carbohydrates — going low-carb, keto, or carnivore, or extending their fasting — one of the most common reasons they feel terrible has nothing to do with the diet being “wrong.” It's electrolytes.

Why Cutting Carbs Changes Your Electrolytes

Here's the chain of events. When you eat a lot of carbohydrates, your blood glucose rises and your body releases insulin to bring it back down. When you cut carbs way back, your insulin levels naturally fall — and that's generally a good thing.

But insulin has another job: it signals your kidneys to hold onto sodium. So when insulin drops, your kidneys start flushing out more sodium and water. At the same time, many people were getting a lot of their sodium from processed foods — which they've now cut out too. Lower insulin, more sodium and water leaving, and less sodium coming in: that's the perfect storm for an electrolyte imbalance.

What It Feels Like

If you're losing too much sodium and fluid when you switch to a very-low-carb way of eating, you may feel it as low energy, headaches, lightheadedness, weakness, or muscle cramps — sometimes bad enough to wake you at night. A lot of people blame the diet when the real culprit is simply electrolytes.

Start With Salt

The simplest fix is often just adding more salt. Salt your food to taste — you want your meals to taste pleasantly salty. When you first cut carbs, that might feel like a surprising amount of salt. Over time, as your body adapts, many people naturally want less. The lesson isn't “everyone needs this exact amount of salt forever” — it's that your sodium needs can change a lot when you dramatically change your diet.

Sodium Isn't the Only Electrolyte

Salt alone doesn't always fix everything, because sodium isn't your only electrolyte. You also need potassium and magnesium. If you're having symptoms that might be electrolyte-related, don't think about sodium in isolation — look at the bigger picture:

• Sodium
• Potassium
• Magnesium
• Hydration
• Your overall diet
• Your individual health

They all work together. Historically, people got varying minerals from natural water sources; today's drinking water can be very different depending on where it comes from and how it's treated, so it's worth being intentional.

A Word of Caution

Electrolytes are powerful, and more is not automatically better. Too much of certain electrolytes or supplements can be harmful — and that matters especially if you take medication or have a health condition. Blood-pressure, kidney, heart, and glucose-lowering medications in particular can interact with big changes in sodium, potassium, or fluid.

So if you're planning major dietary or electrolyte changes and you have any of those conditions, talk with a qualified healthcare professional first.

The Simple Version

If you feel awful in the first days or weeks of cutting carbs, don't immediately decide the diet doesn't work for you. Check the basics: are you getting enough sodium? Are you paying attention to potassium and magnesium? Are you staying hydrated? Very often, one or two small adjustments make a dramatic difference.

This article is for general education and is not medical advice. Individual sodium, potassium, and magnesium needs vary. People with medical conditions or taking medication — particularly blood-pressure, kidney, heart, or glucose-lowering medication — should discuss major dietary or electrolyte changes with a qualified healthcare professional.