If you look at photos of Conor McGregor from late 2015, specifically the morning of the Jose Aldo weigh-in, he doesn't look like a world-class athlete. He looks like a ghost. Sunken cheeks, ribs jutting out like a xylophone, and a deathly, pale complexion that made fans wonder if he’d even make it to the walkout. It was the peak of the "Notorious" era, but it was also the end of an era. The conor mcgregor 145 weight cut is now legendary in MMA circles, not just for the discipline it required, but for the sheer physiological toll it took on the sport's biggest star.
Honestly, he was a massive featherweight. At 5'9" with a 74-inch reach, McGregor carried the frame of a modern-day lightweight or even a small welterweight. Squeezing that much lean muscle into a 145-pound limit was a feat of science and, frankly, a bit of madness.
The Brutal Science of the Featherweight Limit
Most people think "weight cutting" is just a fancy term for dieting. It’s not. When McGregor was preparing for Aldo or Chad Mendes, the actual dieting—the fat loss—happened weeks out. The "cut" is the final, agonizing week where you manipulate water, sodium, and glycogen to trick the body into dumping every ounce of fluid.
Nutritionist George Lockhart, the man who eventually took over McGregor's programs, famously explained how they used the body's own hormones against it. They’d start with "water loading," where Conor would chug up to two gallons of water a day to downregulate aldosterone, the hormone that tells your body to hold onto salt and water. Then, they’d suddenly cut the tap. His body would keep flushing water out even though he wasn't taking any in.
But it gets darker than that.
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Why the 145 Cut Looked So Scary
- Glycogen Depletion: Every gram of glycogen in your muscles holds about 3 to 4 grams of water. By going zero-carb, McGregor's muscles would literally shrink, releasing pounds of water weight.
- The Sauna Suit: The final 5-10 pounds usually came from "active sweating." Imagine being wrapped in plastics, sitting in a sauna, or being buried under piles of towels when you already haven't had a sip of water in 18 hours.
- Skin and Bone: Because McGregor has such low body fat, there was no "buffer." When he lost water, it came directly from his muscle tissue and the fluid around his brain.
It worked. He never missed weight. But at what cost?
The UFC 194 Transformation
The Jose Aldo fight was the masterpiece. 13 seconds. One left hand. But the 24 hours prior were a different kind of fight. McGregor looked "deathly" on the scale. When you see him standing next to Aldo, who was a natural featherweight, the size discrepancy was jarring. Conor looked like he belonged in a different species.
Interestingly, despite looking like a skeleton on Friday, he’d walk into the cage on Saturday night weighing closer to 165 pounds. That’s a 20-pound rebound in a single day. You’ve basically got a guy who spent 10 weeks training as a middleweight, three days dying as a featherweight, and 24 hours resurrecting himself as a lightweight.
Why He Finally Walked Away from 145
The IV ban was a massive turning point. In late 2015, USADA (the UFC's drug testing partner) banned the use of intravenous rehydration. This was a nightmare for "big" cutters like McGregor. Without an IV to pump saline and electrolytes directly into the bloodstream, rehydrating the brain and organs became much slower and more dangerous.
You could see the shift in his face. After the Aldo fight, he immediately moved up to 170 to fight Nate Diaz. Then 155 for Eddie Alvarez.
He realized something vital: he didn't need the "weight bully" advantage to win. His power translated to higher weight classes, and more importantly, he could actually eat.
Health Risks Nobody Mentions
The kidneys take the biggest hit during a conor mcgregor 145 weight cut. When you're that dehydrated, your blood becomes thick—sort of like sludge—making it incredibly hard for the heart to pump. There's also the "chin" factor. The fluid that cushions your brain (cerebrospinal fluid) is the last thing to fully replenish. If you go into a fight dehydrated, you’re much more likely to get knocked out by a shot that you’d normally eat for breakfast.
What We Can Learn from the Notorious Cut
If you're an aspiring fighter or just a fitness enthusiast, looking at McGregor's featherweight run offers some harsh but necessary lessons. Weight cutting is a professional's game, and even then, it's a gamble with your longevity.
1. Professional Help is Non-Negotiable
McGregor didn't do this alone. He had George Lockhart and a team of specialists. If you're trying to drop significant weight for any reason, doing it without monitoring your electrolytes and kidney function is a recipe for disaster.
2. Listen to the "Mirror Test"
If you look like a different person on the scale, your body is screaming at you. McGregor’s transition to 155 and 170 wasn't just about "legacy"—it was a survival move. He was outgrowing the division, and his performance actually improved when he wasn't starving.
3. Performance Over Scale Weight
A "successful" weight cut is one where you still have your "pop" on fight night. If you make the weight but lose your cardio and power, you've lost the fight before it even started.
McGregor’s days at 145 are long gone. Today, he’s a much broader, more muscular version of himself, often walking around near 190 pounds. The ghost of the featherweight division has been replaced by a man who prioritizes power and mass over the extreme advantages of being the "biggest guy in the room."
To really understand the impact of these cuts, you have to look at the longevity of fighters who stayed in one class too long. Many end up with "diminished chins" or chronic kidney issues. McGregor got out at the perfect time.
If you're tracking your own weight or training for a competition, focus on "chronic" weight loss—dropping fat over 8-12 weeks—rather than the "acute" water cut that defined the McGregor era. Your heart, and your brain, will thank you.