In the high-stakes world of Mixed Martial Arts (MMA), the most dangerous battle often takes place before the cage door even locks. It happens in hotel rooms, saunas, and behind closed doors, days before the first punch is thrown. This is the “fight before the fight”: MMA weight cutting.
To the uninitiated, seeing a fighter look gaunt and fragile on the scale only to appear fully revitalized 24 hours later seems like magic. But it is not magic; it is a brutal application of physiology, timing, and suffering. Weight cutting is distinct from weight loss. Weight loss involves shedding fat and building muscle over weeks or months. Weight cutting is the rapid, temporary manipulation of body water and glycogen to hit a specific number on the scale, only to reverse the process immediately after.
For modern fighters, mastering this process is just as critical as perfecting a jab or a double-leg takedown. A botched cut can lead to a diminished gas tank, a fragile chin, or—in extreme cases—organ failure. This guide breaks down the science behind the cut, the strategies elite fighters use, and the physiological risks that loom over every pound shed.
The Physiology of the Cut: How Fighters Shed 20 Pounds in a Week
The human body is approximately 60% water. For a 170 lb (77 kg) male, that equates to roughly 100 lbs (45 kg) of water weight. The goal of a weight cut is to manipulate this water balance without causing permanent damage or affecting performance on fight night. This process generally occurs during “Fight Week,” the final 5-7 days before weigh-ins.
1. Water Loading (Hyper-hydration)
Counterintuitively, the first step to losing water is to drink massive amounts of it. Fighters will often consume 2 gallons (7-8 liters) of water per day early in the week. This puts the body into a state of “diuresis,” suppressing the hormone aldosterone, which is responsible for retaining sodium and water. By flushing the system, the body becomes accustomed to excreting water rapidly.
2. Sodium Manipulation and The Drop
As the week progresses, fighters drastically cut their sodium intake. Because sodium holds onto water molecules, removing it forces the body to flush even more fluid. Simultaneously, they taper their water intake down to almost zero in the final 24 hours. However, because the body is still in “flushing mode” from the water loading phase, it continues to excrete urine despite the lack of incoming fluids. This creates a temporary super-dehydration effect.
3. Glycogen Depletion
Fighters also manipulate their diet by cutting carbohydrates. Carbohydrates are stored in the muscles and liver as glycogen. Every gram of glycogen bonds to approximately 3 to 4 grams of water. By depleting glycogen stores through diet and light exercise, a fighter can passively shed several pounds of water weight without stepping foot in a sauna.
According to data from the UFC Performance Institute, elite fighters cut an average of 6.7% of their body weight in the final 72 hours alone. Lightweights (155 lbs) are often the most aggressive, sometimes cutting over 8% of their body mass in roughly 3 days.
The Sweat Phase: Saunas, Suits, and Suffering
Once the diet and water manipulation have done their work, the final pounds are sweated out. This is the most grueling and dangerous part of the process. Fighters utilize active methods (calisthenics in sweat suits) and passive methods (hot baths and saunas) to wring out the last drops of moisture.
This phase is a delicate balance. Sweat too much, and the blood thickens, forcing the heart to work overdrive to pump sludge through the veins. This cardiovascular strain is why you often see fighters needing support to stand on the scale.
The Dangers: Kidney Failure and The Brain
While strategic dehydration is standard practice, the medical community warns against the severe risks involved. The Association of Ringside Physicians has long cautioned that rapid weight loss affects more than just the muscles.
- Kidney Stress: During a severe cut, blood flow to the kidneys is restricted. Combined with the breakdown of muscle tissue (rhabdomyolysis), this can lead to acute kidney failure.
- The Glass Chin: Perhaps the most critical risk for a fighter is the brain. The brain sits inside the skull cushioned by cerebrospinal fluid (CSF), which is largely water. When a fighter is severely dehydrated, the volume of this fluid decreases, leaving the brain with less protection. A strike that a hydrated fighter might absorb can cause a dehydrated brain to slam against the skull, leading to easier knockouts and increased risk of traumatic brain injury.
- Heat Illness: The inability to sweat due to extreme dehydration removes the body’s natural cooling mechanism, spiking core temperature to dangerous levels.
The Rehydration Window: The Race Against Time
Making weight is only half the battle. The true test is rehydrating effectively in the 24 to 36 hours before the fight. If a fighter rehydrates improperly, they will enter the cage sluggish and bloated. If they rehydrate too slowly, they remain at risk of brain injury.
The USADA IV Ban
Historically, fighters used Intravenous (IV) drips to rehydrate instantly after stepping off the scale. However, in October 2015, the U.S. Anti-Doping Agency (USADA) banned the use of IV infusions over 50mL (unless hospitalized), primarily because IVs can be used to mask performance-enhancing drugs.
This ban forced fighters to rely on oral rehydration. The strategy shifted to consuming electrolyte-rich solutions immediately after weigh-ins. Drinking plain water is often avoided initially because it can flush out remaining electrolytes; instead, fighters sip solutions containing glucose and sodium to optimize fluid absorption in the gut.
Regulations and the Future: The CSAC 10-Point Plan
Recognizing the extreme dangers, regulatory bodies like the California State Athletic Commission (CSAC) have implemented stricter rules. Their “10-Point Plan” includes:
- Fight Day Weight Checks: Fighters cannot gain back more than 10% of their body weight between weigh-ins and the fight. If they do, they may be recommended to move up a weight class.
- Specific Gravity Testing: A urine test to measure hydration levels.
- New Weight Classes: Proposals for more weight classes (like 165 lbs and 175 lbs) to reduce the gaps that force fighters into extreme cuts.
Weight cutting remains a controversial but entrenched part of MMA culture. Until major organizations adopt hydration testing globally (similar to ONE Championship), fighters will continue to push their physiology to the brink in search of a size advantage.
FAQ
Why do MMA fighters cut weight?
Fighters cut weight to compete in a lighter weight class than their natural walking weight. The goal is to rehydrate after weigh-ins and enter the cage significantly heavier and stronger than their opponent, gaining a size and leverage advantage.
Is weight cutting dangerous?
Yes, extreme weight cutting is dangerous. It places immense strain on the kidneys and cardiovascular system. Furthermore, competing while dehydrated reduces the fluid cushioning the brain, increasing the risk of concussions and knockouts.
How much weight do fighters typically cut?
According to UFC Performance Institute data, fighters typically cut around 6-8% of their body weight during fight week, but some extreme cuts can exceed 10-15% of their body mass.
What is the difference between weight cutting and losing weight?
Losing weight involves long-term fat loss and muscle changes. Weight cutting is the rapid, temporary loss of water weight and glycogen specifically for the official weigh-in, which is immediately regained through rehydration.
Are IVs allowed for rehydration in the UFC?
Generally, no. USADA and most athletic commissions prohibit IV infusions over 50mL unless administered in a hospital setting or for a specific therapeutic exemption. This rule was implemented because IVs can be used to mask the presence of banned substances.