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The New Science of Extreme Weight Loss

The UFC's top nutritionist explains four lessons you can learn from pre-fight weight cutting—where fighters lose and then gain back up to 20 pounds in 5 days.

The New Science of Extreme Weight Loss

Summary of this post

  • UFC fighters lose up to 20 pounds in five days leading to weigh-in for a fight.

  • We’ll explain the science of how they do it and what you can learn from it.

  • This is important for the average person because it can help you understand:

    • What to do when your weight changes day-to-day.

    • The truth about low-carb diet results.

    • How “calories in, calories out” is accurate but misses critical information.

    • How to lose weight in a way that makes you look and feel better—for the long haul.


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  • The great and wise John Delony and I will be at the Cornish Pasty Co. in Las Vegas this Thursday night starting at 7pm. We’ll be hanging out, signing books, and answering questions. Swing by if you’re in the area.

Podcast version of this post (Spotify and Apple Podcasts)

The post

UFC 300 happens this Saturday. It’s a milestone for the federation.

Whenever a big fight comes along, I’m fascinated by how fighters change their weight leading up to the fight.

You probably know that fighters are divided by weight classes. The UFC conducts official weigh-ins Friday morning before their Saturday night fights. This ensures that fighters meet their weight class’ cutoff.

For example, flyweights must weigh in at or under 125 pounds, lightweights at or under 155 pounds, light heavyweights at or under 205 pounds.

But fighters aren’t actually at those weights when they step into the octagon to fight on Saturday night. They’re much heavier.

Fighters go through a grueling process of cutting weight for the weigh-in—losing 10 or even up to 20 pounds in five days to reach their weight class.

Then they’ll gain it all back before they step into the octagon. This allows them to fight at a heavier-than-advertised weight, which gives them a size advantage. The change can be dramatic. For example, here’s Connor McGregor for a fight in 2015:

Photo Credit: The Sun

For example, a fighter in the lightweight division might officially weigh in at 155 pounds on Friday morning, then step out into the octagon weighing 172 pounds on Saturday night.

Today, we’re covering the science of this kind of extreme weight-cutting. There are good lessons we can take from it.

  • The new science of extreme weight loss.
  • Four lessons you can learn from fighters so you can eat smart and feel better—for the long haul.

Let’s roll …

The new science of extreme weight loss

Section summary

Weight cutting used to be dangerous. Tyler Minton helped pioneer smarter weight cutting-science after ending up in the hospital after a fight cut.

The details

To understand this topic, I called my friend Tyler Minton.

Tyler is a former fighter, performance nutritionist, and pioneer in weight-cutting science.

He’s been the performance nutritionist for UFC greats like Khabib Nurmagomedov, Max Holloway, Daniel Cormier, and many more. He’s also the author of Fueling Fight Week: The Science of Eating for a Weight Cut.

The revolution in weight-cutting science started around 2010. The methods before that were, Minton explained, “eat and drink less, and run more while wearing a trash bag or sauna suit so you’d sweat until you hit the weight.”

But this tanked fighter performance and was also dangerous. “I ended one fight so weak my knees bucked when they raised my hand. I also ended up in the hospital after a cut—and I’d done everything that people said to do perfectly. I realized, ‘What’s the point of making weight if you get in the octagon and can’t perform or miss the fight because you’re in the hospital? This isn’t a Biggest Loser challenge. We have to win the fight.”

So Minton paused his fighting career and went on a knowledge quest, conducting research and consulting some of the country’s top nutrition minds. A year later, he’d figured out how to cut weight smarter.

“I started making weight really easily. And I was getting in the cage and felt great,” he said. Other fighters started contacting him for help. He decided to follow the call and go all-in on performance nutrition.

The weight-cutting timeline

In short

Fighters don’t lose fat or muscle in the process. They lose water. They do this by leveraging a tactical timeline that involves manipulating their water and diet to purge water from their bodies.

The details

Weight cutting isn’t like normal weight loss. Fighters don’t lose fat or muscle—they lose water.

Roughly 50 to 70 percent of your body is water. That water is necessary for every cell, tissue, and organ to function. If you weigh 150 pounds, 75 to 105 pounds of your weight is water.

But the amount of water in your body is constantly changing. It depends on:

  • What you eat and drink.
  • How active you are.
  • How you sleep.
  • And much, much more.

Minton helps fighters shed water safely before a fight. Then he helps them put it all back so they can fight heavier and hit harder. Here’s how he does it:

120 hours before weigh-in: reduce water, salt, and exercise

The water formula

Because cutting is entirely about losing water, fighters can’t drink as much as they’d like.

“We have a pretty simple formula to begin to reduce water leading to the weigh-in,” said Minton. “The formula is: the fighter’s body weight in kilograms times point one.”

So, for example, a 180-pound/82-kilo fighter’s formula would be: 82 x 0.1 = 8.2.

Hence, that fighter would drink roughly eight liters of water a day.

The salt formula

Minton also has fighters reduce their sodium intake.

Sodium helps our muscles and brain function. It’s necessary for survival.

But it also helps you retain water. That’s good for hydration, but it can work against you if you’re trying to shed water weight.

In the past, fighters would try to cut out sodium entirely. But because sodium helps your muscles function, that method led fighters to experience muscle cramps and performance drops.

Instead, Minton cuts the fighter’s sodium to just below 1,000 milligrams. That’s enough of a drop to stimulate water loss, but it also prevents issues that come from trying to cut salt altogether.

For context, the average person consumes ~3,000 to 4,000 milligrams of sodium each day. (Fun fact: humans only need about 300mg a day to survive.)

Train easier

Fighters have been training hard in the months leading up to the fight.

“But at this point, as we say in Tennessee,” said Minton, “The hay is already in the barn. We’re not going to improve a fighter’s fitness the week before the fight. Training hard during the intense cut is only going to burn them out for fight day.”

Fighters will work on some light technique. Or go for a long walk. But it’s relaxed so the fighter is at 100 percent on fight night.

72 hours before weigh-in: reduce carbs and fiber

Eat more fat and fewer carbs

“Tuesday is usually when a fighter arrives in Las Vegas or wherever the fight is, and that’s when we start to modify their diet,” said Minton.

In the past, fighters would simply eat less. But that just made them miserable and tanked their performance.

Instead of changing the “how much,” Minton tweaks the “what.”

As a fighter trains hard in the months leading to a fight, their diet is mostly carbohydrates (about 60 percent).

But carbs cause your body to retain more water. One study found that “each gram of glycogen (carbs) is stored in human muscle with at least three grams of water.”

So he cuts the fighter’s carbs and has them eat more fat.

“We take advantage of the fact that glycogen (carbs) hold water and fat doesn’t—fat is hydrophobic,” Minton explained.

The fighters start eating 60 percent of their calories from fat. Roughly 35 percent come from protein and only about 5 percent come from carbs.

Their body purges water even though they’re eating the same amount of calories.

“The fighters definitely aren’t eating the foods they want—a lot of meat and oils—but they feel great because they’re still getting plenty of calories.”

The carbs fighters do eat are usually berries or honey before light exercise or a press conference.

“Going low-carb can lead to temporary brain fog,” he said. “So we’ll give the fighter some carbs right before a big press conference or media event so they can think straight.”

Remove fiber

Fighters used to eat lots of vegetables before fights. The idea was that vegetables would fill them up but not add many calories. That was true, but fiber also acts like a sponge soaking up water.

Minton said:

So we eliminate fiber from the fighter’s diet. This lowers the bulk in their stomach. It can take up to three days for food to pass completely through their system.

By lowering the bulk in their stomach, fighters will lose around two percent of their total body weight. So if you have a 200-pound fighter, they're going to lose about four pounds that week purely by dropping their fiber.

24 hours before weigh-in: reduce water even more, sweat remaining weight, sleep well

These 24 hours before weigh-in are critical. The goal is to dry up the sponge. A fighter still may have five or six pounds to lose before the weigh-in.

Reduce water even more

“Now we change the water formula so it’s their bodyweight in kilograms times 0.01, which is usually about 20 to 30 ounces for the entire day,” said Minton.

“But the fighter is still decently hydrated because we haven’t completely cut out sodium. We haven’t completely cut out carbs. And we didn’t train hard all week.”

Sweat out the remaining weight

People sweat differently. So Minton conducts sweat rate testing during training camp and records all of his fighters’ sweat rates.

This data allows him to get tactical by having them sweat out the remaining water by sitting in a hot tub.

Minton said, “So I know exactly how much water a fighter will lose if we put them in a 104-degree tub for 30 minutes. I know exactly how much they’ll lose if we stick them in a 130-degree tub for 45 minutes.”

Prioritize sleep

Fighters stop drinking water Thursday night.

“Thursday night I usually give the fighters ice cream or frozen yogurt,” he said. “The fighters often worry about the carbs. But at this point we’re not drinking any water. So those carbs don’t have water to cling to and aren’t going to cause water retention.”

“And that ice cream is a huge psychological boost—cutting is miserable. And the carbs also help them sleep better.”

Sleep during this stage is critical—we lose a lot of water during sleep, and adequate sleep helps them perform better during the fight.

The zero-hour: weigh-in

Friday morning before weigh-in is simple: The fighter gets no food or water. They’ve done the work and met their goal.

So they step on the scale, make weight, flex for the crowd, then get ready to rehydrate.

36 hours after weigh-in: rehydrate and eat carbs slowly

After the weigh-in, fighters are thirsty and hungry.

“They think they can just eat and drink whatever now,” said Minton. “But we need to rehydrate and feed them slowly so they don’t get stomach issues.”

Drink first

For the first hour, fighters slowly sip about three liters of different electrolyte drinks, starting with drinks similar to no-sugar Gatorade and ending with full-sugar Gatorade.

Eat slow and smart

“After the fighter is hydrated and starts processing through those liquids, we introduce some foods,” said Minton.

They start with candy. No kidding. “At this point we’re just trying to load sugar slow and steady so we don’t get stomach issues.”

For example, gummy bears because they’re high in carbs and easily digestible. Then he moves into dried fruits and bread with jelly.

After two hours, the fighter eats their first real meal. “It’s usually low in fat because fat slows the absorption of sugars. So something like sushi or pasta.”

Their eating shifts back to being like it was in the months of preparation: healthy but higher in carbs.

The morning of the fight, “we splurge a bit,” said Minton. “I’ll be like, hey, let’s go get some pancakes or french toast.” That gives fighters a psychological boost and lots of calories before (but not too close to) the fight.

The fight

The fighters have their final meal five hours before the fight, then some high-carb, low-fiber snacks until they walk out.

“We want the food broken down and not heavy in their stomach. It’s usually lean meat and rice.”

When enter the octagon, they’re 10 to 20 pounds heavier than they were Friday morning.

P.S.: For those most interested in the science of fight weight cutting, please read Minton’s book, Fueling Fight Week: The Science of Eating for a Weight Cut.

4 lessons so you can eat smart and feel better—for the long haul

Section summary
  1. Avoid crash dieting because it alters your metabolism, leading you to regain even more weight.
  2. Understand that low-carb and keto diets leverage water weight loss to make big claims.
  3. Focus on protein and whole foods as you lose weight.
  4. Don’t worry about your daily weight changes—it’s just water.
The details

1. Don’t crash diet

“The biggest takeaway for the average person is that you shouldn’t do anything like what fighters do to cut weight,” said Minton.

It sounds obvious, but people do it all the time. For example, we aim to lose 10 pounds before a vacation or wedding.

So we jump on some extreme diet and exercise far more. And we do lose weight.

But it’s not sustainable. After the event, you go back to eating like you did before. “But now,” Minton said, “you’ve created some problems.”

Crash dieting alters your metabolism. “Your metabolism lowers as a survival mechanism when you crash diet,” he said. “Then you go back to your normal diet, but your metabolism is lower. This explains why people often gain more weight back after a diet.”

It also messes with your hunger signaling, so you might eat even more than you did before the diet.

A better approach: Try to lose weight across a year, not a few weeks.

2. Understand how crash diets leverage water weight

The ketogenic and low-carb diets exploded in popularity because they lead to rapid weight loss.

You’ve probably seen the ads and testimonials for those diets—”Lose 10 pounds in one week.”

And while the number on the scale does drop significantly and quickly on those diets, it’s not the weight we care about.

Recall what we just learned about how carbohydrates lead you to retain more water and fat doesn’t.

When people switch to a low-carb, high-fat diet, all that initial weight loss is from water. It’s not actual fat loss.

3. Weight loss is about calories—but looking and feeling better takes more thought

Weight loss is calories in and calories out. So in theory, you could eat only McDonald’s and lose weight so long as you ate fewer calories than you burned.

But the real goal of weight loss isn’t to see a number on a scale change. Your real goal is probably to look and/or feel different.

Minton’s rule is:

  • Calories determine your weight, or the number on the scale.
  • Macronutrients—or carbs, fat, and protein—determine how you look.
  • Micronutrients—the vitamins and minerals of your food—determine how you feel.

The lesson:

  • Eat the amount of food, or calories, that helps you get to the weight you’d like to be.
  • Eat enough protein to maintain muscle mass and look your best as your weight changes.
  • Eat mostly single-ingredient foods like fruits, vegetables, whole grains, and lean proteins so you get all the vitamins, minerals, etc to feel great as your weight changes.

4. Don’t trust daily weight changes—trust monthly and yearly changes

Let’s say you weigh yourself Saturday morning, and you weigh 150 pounds. But then you weigh yourself Sunday, and the scale says 155 pounds.

“People will often freak out and say ‘I gained five pounds yesterday,’” said Minton. “So this is when I like to have the conversation, ‘a pound of fat has 3,500 calories. So do you think you ate 5 times 3,500, or 17,500 extra calories yesterday? Probably not.”

We just learned how water weight can change fast. Day-to-day weight changes are entirely due to water weight. And all sorts of strange things can lead you to gain or purge water:

Minton said, “Maybe you slept a little bit less, or haven't used the bathroom, or ate more sodium. Or maybe it’s your menstrual cycle.”

True fat losses and gains happen over weeks, months, and years. If you track your weight, you want to play the long game.

“I had a client last year who lost 60 pounds in a year,” Minton said. “There was one month she did everything right and gained two pounds. And most people would have given up, but she trusted and believed in the process. Her body was just doing some funky stuff with water that month—she persisted and kept losing.”

Have fun, don’t die, trust the process (and it’s a long process).


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