Electrolytes for Weight Cutting: Sodium, Potassium & Timing

Contents

Yes, you should use electrolytes when cutting weight, but at the right time. Keep sodium normal through camp, reduce it (never to zero) in the last days if your plan includes a water cut, and put it straight back after the weigh-in. For the refill, the ACSM recommends drinking about 150% of the fluid you lost, with oral rehydration solutions or drinks containing around 50–60 mmol of sodium (Burke et al., 2021).

Electrolytes are the part of the weight cut most fighters fumble. They control how much water your body holds on to, and so both your weigh-in and your performance.

What do electrolytes do in a weight cut?

Electrolytes, above all sodium, decide where water goes in your body. Where sodium goes, water follows. That’s why salt intake moves the scale in fight week, and why you can’t rehydrate properly on plain water.

The electrolytes that matter for a fighter:

• Sodium (and chloride): the main electrolytes in sweat and the big fluid regulators.
• Potassium: works mainly inside your cells and is key for muscle and heart function.
• Magnesium: involved in muscle and nerve function; lost in sweat only in tiny amounts.

Here’s what sweat typically contains, according to a comprehensive review of sweat physiology (Baker, 2019):

Electrolyte	Typical concentration in sweat	Roughly per litre of sweat
Sodium (whole-body)	~20–80 mmol/L	~460–1,840 mg
Chloride (whole-body)	~20–70 mmol/L	—
Potassium	2–8 mmol/L	—
Magnesium	0.02–0.40 mmol/L	—

(Sodium conversion: 1 mmol = 23 mg.) Sodium is by far the biggest loss, and it varies a lot between people. The ACSM’s fluid-replacement position stand stresses that sweat rates and sweat electrolyte content vary considerably between individuals, so your needs aren’t the same as your teammate’s (Sawka et al., 2007).

Should you drink electrolytes when cutting weight?

Yes, at two points: during hard training in camp, and after the weigh-in. In between, in the final days before the weigh-in, many fighters deliberately lower sodium.

• During camp: the goal of drinking during exercise is to avoid losing more than 2% of body weight as water and to avoid big shifts in electrolyte balance, and drinks with electrolytes and carbohydrate can beat water alone in some situations (Sawka et al., 2007). You can estimate your own sweat rate by weighing yourself before and after training.
• Before the weigh-in: sodium restriction combined with water loading increases urine output and acute water loss (ISSN, 2025). This is the only phase where less is the goal.
• After the weigh-in: sodium goes back in, fast. See the timing table below.

Sodium: down, then up again

Lower sodium before the weigh-in, then load it back afterwards. That’s the central maneuver, in two phases:

1. Down in the final days. When you cut salt while drinking plenty, your body excretes more fluid. This works together with a water taper; see our water loading guide.
2. Up again after the weigh-in. Now you want the water back in your body. The ACSM recommends replacing lost electrolytes, especially sodium, to help fluid re-balance quickly and minimise urine losses (Burke et al., 2021).

“Sodium down” means lower salt for a few days, not zero salt. Neither the ISSN nor the ACSM statement gives a single daily sodium target for this phase, so don’t copy extreme numbers from the internet. And be careful with the combination of very low salt and very high plain-water intake: the ACSM lists a small risk of hyponatraemia (low blood sodium) with water loading (Burke et al., 2021).

The opposite extreme is also dangerous. In a documented MMA case, severe dehydration in the last 24 hours before a weigh-in pushed blood sodium to 148 mmol/L (hypernatraemia), alongside acute kidney injury (Kasper et al., 2019).

Electrolyte timing by phase

Match your sodium and fluid to the phase you’re in. A starting framework, not a prescription:

Phase	Sodium	Fluid	Source
Camp weeks	Normal, moderate salt; electrolytes in long or hot sessions	Enough to limit losses to under ~2% body weight per session	Sawka et al., 2007
Final days before weigh-in	Lower salt, not zero	Per your water-loading plan	ISSN, 2025
Straight after weigh-in	Oral rehydration solution or ~50–60 mmol sodium per litre, plus salty food	1–1.5 L per hour at first; aim for ~150% of what you lost overall	ISSN, 2025; Burke et al., 2021

In mg, 50–60 mmol of sodium is about 1,150–1,380 mg. Check the label of your drink for its sodium per litre. The ACSM also notes that electrolyte replacement matters more when you dehydrated by sweating (sauna, sweat suits) than by simply drinking less, because sweat takes sodium with it (Burke et al., 2021). More on that in our sauna weight cut guide, and the full refill plan is in rehydrate after the weigh-in.

How to drink after the weigh-in

Drink a decent amount straight away, then keep sipping, with sodium in every step. The ACSM gives practical pointers for the recovery window (Burke et al., 2021):

• Start with a bigger drink (for example around 10 mL per kg of body weight) right after the weigh-in, then smaller amounts at regular intervals. A fuller stomach empties faster, and front-loading means you don’t need to gulp fluid just before you fight.
• Pair fluid with sodium: an oral rehydration solution or salty food alongside other drinks.
• Add some protein to a drink or meal: it can help your body retain the fluid.
• Sip rather than chug later on: slower, more frequent drinking reduces urine losses.

It may not be possible to replace everything you lost before the fight, which is one more reason to keep the cut small in the first place.

What electrolytes should you take?

Mainly sodium; the rest usually comes from food.

• Sodium: an oral rehydration solution or an electrolyte drink with a meaningful amount of sodium, plus salty food after the weigh-in.
• Potassium: keep a normal intake through food such as potatoes, bananas, vegetables and beans. Don’t take potassium supplements on your own: imbalances can affect the heart.
• Magnesium: many fighters take it for cramps, but a Cochrane review found it unlikely to meaningfully prevent cramps in older adults and found no trials on exercise-associated cramps. Oral magnesium was mostly linked to gut side effects such as diarrhoea (Garrison et al., 2020), which is the last thing you need in fight week.

Why do cramps happen during a cut?

Usually from dehydration plus sodium lost in sweat. The ACSM notes that, depending on how you lose water, electrolyte imbalances may occur and increase the risk of muscle cramps; diuretics in particular carry that risk (Burke et al., 2021).

The fix is rarely more plain water. It’s fluid with sodium, a normal diet, and not cutting so much water in the first place.

Can electrolyte drinks help with weight loss?

No. Electrolytes don’t burn fat. Their job is to help your body hold on to water, which is the opposite of what you want before a weigh-in and exactly what you want after it. Many sports drinks also contain sugar, which adds calories during a diet.

If you’re trying to lose body fat, electrolyte drinks are only useful for keeping you hydrated in training. For the fat-loss side, see fight camp nutrition.

MyFightPrep helps you track fluids and electrolytes through fight week, from the taper before the weigh-in to the refill afterwards — free.

Important

This guide is general information, not medical advice. Manipulating salt and fluids can disturb your body’s balance, and both too little and too much sodium can be dangerous, especially combined with a hard water cut. If you’re under 18, new to the sport, take medication (for example for blood pressure), or have heart or kidney problems, don’t manipulate sodium or fluids without your coach and a doctor. If you experience confusion, a severe headache, repeated cramps or an irregular heartbeat, stop and seek help.

Frequently asked questions

Should I drink electrolytes when cutting weight?

Yes, but timing matters. Keep a normal intake during camp, reduce sodium (not to zero) in the final days if that's part of your plan, and drink an electrolyte or oral rehydration solution straight after the weigh-in. The ACSM recommends replacing sodium along with fluid so your body holds on to what you drink.

What electrolytes should I take?

Sodium is the one that matters most, because it's the main electrolyte lost in sweat. After the weigh-in, the ACSM points to oral rehydration solutions or drinks with about 50–60 mmol of sodium per litre, plus salty food. Get potassium from normal food, and don't rely on magnesium supplements for cramps: the evidence for them is weak.

Can electrolyte drinks help with weight loss?

No. Electrolytes don't burn fat. They help your body hold water, so they can actually make the scale go up for a while, and many sports drinks also contain sugar and calories. Use them for rehydration, not as a diet tool.

Sources

This guide is based on the works below. Numbers in the text refer to them.

1. Burke LM, Slater GJ, Matthews JJ, Langan-Evans C, Horswill CA (2021). ACSM Expert Consensus Statement on Weight Loss in Weight-Category Sports
2. Ricci AA, Evans C, Stull C, et al. (2025). International society of sports nutrition position stand: nutrition and weight cut strategies for mixed martial arts and other combat sports
3. American College of Sports Medicine; Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS (2007). American College of Sports Medicine position stand. Exercise and fluid replacement
4. Baker LB (2019). Physiology of sweat gland function: The roles of sweating and sweat composition in human health
5. Garrison SR, Korownyk CS, Kolber MR, et al. (2020). Magnesium for skeletal muscle cramps
6. Kasper AM, Crighton B, Langan-Evans C, et al. (2019). Case Study: Extreme Weight Making Causes Relative Energy Deficiency, Dehydration, and Acute Kidney Injury in a Male Mixed Martial Arts Athlete