Electrolytes and Weight Cutting: Sodium, Potassium and Fluid Balance

Electrolytes are the part of the weight cut most people fumble. They control how much water your body holds on to — and therefore both your weigh-in and your performance. Understand sodium, potassium and fluid balance, and you understand half of a good cut.

What do electrolytes do?

Electrolytes are minerals that, among other things, regulate fluid balance and muscle function. The most important ones for a fighter:

• Sodium (salt): the big fluid regulator — where sodium goes, water follows.
• Potassium: sodium’s counterpart inside the cells; important for muscle function.
• Magnesium: involved in muscle and nerve function, often linked to cramps.

The point is not to remove them — that’s dangerous — but to manage them wisely during fight week.

Sodium: down, then up again

The central maneuver in electrolytes and weight cutting is to manipulate sodium in two phases:

1. Down in the days before the weigh-in. When you cut salt, the body increases fluid excretion and you lose water weight. This works together with water loading — see our water loading guide.
2. Up again after the weigh-in. Now you want the water back in your body. Without salt you won’t hold on to the fluid you drink. See our guide to refueling after the weigh-in.

Important: “sodium down” means low salt for a few days, not zero salt. Complete salt depletion combined with a hard water cut can cause dangerously low sodium (hyponatremia), especially if you’re also drinking a lot of plain water at the same time.

Potassium and magnesium

• Potassium: keep a normal intake through food — banana, potato, vegetables, beans. Don’t mess aggressively with potassium on your own; imbalances here can affect the heart.
• Magnesium: many fighters take a supplement during fight week against cramps. Stay in normal doses and don’t experiment during fight week itself without having tried it before.

Cramps — why they happen

Cramps during fight week are typically caused by a cocktail of dehydration and loss of sodium and potassium through sweat — see our guide to sauna and weight cutting. The countermeasure is rarely more plain water; it’s fluid with salt and a normal intake of potassium and magnesium.

Practical doses

Rough starting points — not prescriptions:

Phase	Sodium	Fluid
Normal camp weeks	Normal, moderate salt intake	By thirst + plan
Last 2–3 days before weigh-in	Low salt	Tapered down (water loading)
After weigh-in	Salt back — sports drink/electrolytes	about 1 liter per hour

A regular electrolyte mix or sports drink for the refuel typically contains plenty of sodium — you rarely need to measure in milligrams.

Important

This guide is general information, not medical advice. Manipulating salt and fluids can disturb the body’s balance, and both too little and too much sodium can be dangerous — especially combined with a hard water cut. If you’re young, new to the sport, take medication, have heart or kidney problems, or are in doubt, do it together with your coach and a doctor. If you experience confusion, severe headache, cramps, or an irregular heartbeat, stop and seek help.

MyFightPrep helps you keep track of fluids and electrolytes throughout fight week — from the taper before the weigh-in to refueling afterward — free.