Water Loading for a Weight Cut: Protocol & Schedule
By Simon Jounan · Founder of MyFightPrep · Kickboxer & Muay Thai fighter
Published · Updated · 7 min read
Water loading for a weight cut: what the research shows (about 0.6 % extra loss), a day-by-day example schedule from the study protocol, and the risks.
Contents
Water loading means drinking much more than normal for a few days, then sharply cutting fluid the day before the weigh-in. Your body keeps excreting water for a while after the intake drops. In the best-known controlled study in combat athletes, this produced about 0.6 % of body mass more weight loss than fluid restriction alone (Reale et al., 2018). That is a modest tool for the last part of a cut, not a way to make up for a failed camp.
Water loading is one of the most used and most misunderstood fight-week methods. Here is what it does, what the research actually found, a day-by-day example and when you should skip it.
What is water loading?
Water loading is a period of very high fluid intake followed by fluid restriction before the weigh-in. The goal is to increase urine output so you lose water without extra sweating (Ricci et al., 2025).
The mechanism is not fully mapped. The researchers who tested it suggest that changes in water channels in the kidney (aquaporins), regulated by the hormone vasopressin, may partly explain the extra water loss (Reale et al., 2018). In simple terms: after days of flooding your system, your kidneys stay in “excrete” mode for a while after you stop.
It is common. In a survey of 637 combat athletes cited by the ISSN, more than 60 % of MMA, Muay Thai, kickboxing and boxing athletes reported water loading, and 53 % across all combat sports (Ricci et al., 2025).
Does water loading work? What the research shows
Yes, a little, under controlled conditions. Reale and colleagues split 21 male combat athletes into a water loading group (n = 11) and a control group (n = 10). Both ate the same standardised, energy-matched diet for 6 days (Reale et al., 2018):
| Water loading group | Control group | |
|---|---|---|
| Days 1–3 fluid | 100 mL per kg per day | 40 mL per kg per day |
| Day 4 fluid | 15 mL per kg | 15 mL per kg |
| Days 5–6 | Same rehydration protocol | Same rehydration protocol |
| Result after restriction | ~0.6 % of body mass more loss | Reference |
According to the ISSN’s summary of the study, body mass loss was 3.2 % in the water loading group versus 2.4 % in the control group (Ricci et al., 2025). Blood urea and electrolytes stayed within reference ranges, and physical performance did not differ between the groups (Reale et al., 2018).
The ISSN lists sodium restriction and water loading as effective ways to induce increased urine output and acute water loss (Ricci et al., 2025). A review likewise describes water loading as a safe and effective way to manipulate body mass by about 3 % in grappling athletes. The same review calls for more research in striking athletes and for cuts beyond 4 % (Barley et al., 2019).
Keep the evidence in proportion: the key trial is one small, controlled study of 21 male athletes. The ACSM consensus still describes water loading as experimental and likely to achieve a smaller net loss than other techniques (Burke et al., 2021).
How much weight can you lose with water loading?
Expect a small extra loss, around half a kilo for a mid-weight fighter. 0.6 % of body mass is:
| Body weight | ~0.6 % extra loss |
|---|---|
| 60 kg (132 lb) | ~0.36 kg (0.8 lb) |
| 75 kg (165 lb) | ~0.45 kg (1.0 lb) |
| 90 kg (198 lb) | ~0.54 kg (1.2 lb) |
That is the extra over fluid restriction alone, based on Reale et al., 2018. It is enough to shave the last bit off a well-planned cut. It is not enough to save a cut that started too late. For the bigger picture, see how much water weight you can lose.
Example water loading schedule (based on the study protocol)
This is an example derived from the research protocol, not a personal prescription. It assumes a weigh-in on the morning of day 5. Spread the fluid evenly through the day rather than drinking large amounts at once.
| Day | Protocol (per kg) | 60 kg athlete | 75 kg athlete | 90 kg athlete |
|---|---|---|---|---|
| Day 1 (e.g. Monday) | 100 mL/kg | 6.0 L | 7.5 L | 9.0 L |
| Day 2 (Tuesday) | 100 mL/kg | 6.0 L | 7.5 L | 9.0 L |
| Day 3 (Wednesday) | 100 mL/kg | 6.0 L | 7.5 L | 9.0 L |
| Day 4 (Thursday) | 15 mL/kg | 0.9 L | ~1.1 L | ~1.35 L |
| Day 5 (Friday) | Weigh-in, then rehydrate | — | — | — |
Volumes are simple arithmetic: body weight × mL per kg. In the study, athletes also ate a standardised diet and trained under supervision. Your real fight week will differ, which is why you should rehearse the protocol in camp first.
Sodium: don’t cut salt to zero while drinking this much. The ISSN suggests that if you reduce sodium in fight week, you should not go below about 2,300 mg per day, because you keep losing sodium in sweat (Ricci et al., 2025). More in our guide to electrolytes and weight cutting.
Water loading vs. sauna and plain fluid restriction
Water loading is one of the gentler ways to lose water, but it only covers part of a cut. The ACSM consensus compares the common methods (Burke et al., 2021):
- Plain fluid restriction is simple, but brings strong thirst and a slower rate of loss than sweating.
- Water loading may make a low-calorie fight week easier on the appetite, but it is still experimental and likely gives a smaller net loss.
- Passive sweating (sauna, hot baths, sweat suits) loses plasma volume first, and the heat raises the risk of overheating.
In practice, water loading is usually combined with lower fibre, carbs and sodium, so the hot methods can stay small or be skipped. See our sauna weight cut guide for where that line is.
Risks: hyponatremia and extreme protocols
The main safety concern with water loading is low blood sodium (hyponatremia), and the risk grows the more you drink. The ISSN notes that fluid intake beyond what your kidneys can excrete may lead to hyponatremia (Ricci et al., 2025). The ACSM lists a small risk of hyponatremia among the disadvantages of water loading (Burke et al., 2021). The controlled study specifically looked for it, and blood sodium stayed within the normal range (Reale et al., 2018). That was a supervised setting with a fixed protocol, though.
The danger grows when water loading becomes part of an extreme cut. In a published case study, an elite MMA athlete drank 8 litres a day for 4 days, then 250 mL on day 5, after 7 weeks of heavy dieting and before 20 hours of fasting and dehydration. He lost 18.1 % of his body mass in total. The severe dehydration at the end caused abnormally high blood sodium and acute kidney injury (Kasper et al., 2019). Water loading didn’t cause that alone, but it shows how quickly a “protocol” becomes dangerous when every lever is pulled at once.
When should you NOT water load?
- You are already on weight. There is nothing to gain.
- Your weigh-in is on fight day. With only a few hours to refuel, extra dehydration costs more than it gains.
- Your event tests hydration at the weigh-in. ONE Championship, for example, requires a urine specific gravity of 1.025 or lower before you are allowed to weigh in (ONE Championship).
- You are under 18, new to the sport, sick or have kidney or heart problems. Don’t.
- You have never tried it before. Never test water loading for the first time in fight week. Run a dress rehearsal in camp with your coach.
After the weigh-in
Rehydrate with sodium, not just plain water, and refuel with carbohydrate. The ISSN recommends oral rehydration solutions at about 1–1.5 litres per hour right after the weigh-in, followed by fast-acting carbs at up to 60 g per hour (Ricci et al., 2025). The full plan is in how to rehydrate after the weigh-in. For how water loading fits into the rest of fight week, see how to cut weight for a fight.
MyFightPrep has built-in water loading planning that sets your daily water targets toward the weigh-in, plus hydration tracking for the refuel afterward — free during the beta.
Important
Water loading changes your body’s fluid and sodium balance and is not risk-free. This guide is general information, not medical advice. Do not water load if you are under 18, have a medical condition or take medication that affects fluid balance, and plan any protocol with your coach and a doctor or sports dietitian. Stop and seek medical help if you develop a headache, nausea, vomiting, confusion, swelling, dizziness or cramps during water loading or a weight cut.
Frequently asked questions
How much weight can you cut with water loading?
Less than most people think. In a controlled study in combat athletes, water loading produced about 0.6 % of body mass more loss than simple fluid restriction, roughly 0.45 kg for a 75 kg fighter. It closes a small gap; it does not rescue a failed cut.
How do you water load for a weight cut?
In the research protocol, athletes drank 100 mL per kg of body weight per day for three days, then cut to 15 mL per kg on day four, with weigh-in measurements on day five. That is about 7.5 litres a day, then about 1.1 litres, for a 75 kg athlete. Try it in camp with your coach before using it for a fight.
How much water weight can you cut in one day?
The ISSN position stand puts supervised acute water loss at about 2 to 4 % of body mass within the 24 hours before weigh-in. How much is sensible for you depends on how long you have to rehydrate before the fight.
Is water loading dangerous?
In a controlled study, blood electrolytes stayed within normal ranges, but experts still describe water loading as experimental with a small risk of low blood sodium (hyponatremia). Extreme versions combined with severe dehydration have caused serious harm, including acute kidney injury.
Sources
This guide is based on the works below. Numbers in the text refer to them.
- Reale R, Slater G, Cox GR, Dunican IC, Burke LM (2018). The Effect of Water Loading on Acute Weight Loss Following Fluid Restriction in Combat Sports Athletes
- Ricci AA, Evans C, Stull C, Peacock CA, French DN, Stout JR, et al. (2025). International Society of Sports Nutrition Position Stand: Nutrition and Weight Cut Strategies for Mixed Martial Arts and Other Combat Sports
- Burke LM, Slater GJ, Matthews JJ, Langan-Evans C, Horswill CA (2021). ACSM Expert Consensus Statement on Weight Loss in Weight-Category Sports
- Barley OR, Chapman DW, Abbiss CR (2019). The Current State of Weight-Cutting in Combat Sports
- Kasper AM, Crighton B, Langan-Evans C, Riley P, Sharma A, Close GL, Morton JP (2019). Case Study: Extreme Weight Making Causes Relative Energy Deficiency, Dehydration, and Acute Kidney Injury in a Male Mixed Martial Arts Athlete
- ONE Championship (2026). Martial Arts: weigh-in and hydration testing rules