Rapid Water Loss vs Sustained Fat Shedding: A Deep Dive

Did you know the majority of your body’s weight is actually water?  

Approximately 70% of your cells are water, and around 60% of your entire body mass is actually H2O.  This is the main reason the number on the scale can bounce around so much from day to day. 

That’s why I encourage people to focus on the long-term trend and ignore the day-to-day water weight fluctuations while guiding our Optimisers to lose body fat and improve their metabolic health over the long term in our Macros Masterclass and Data-Driven Fasting Challenges.   

I regularly remind people that rapid weight loss never lasts; there are no short-term fixes to long-term habits that have created problems.  Instead, it’s about forming sustainable practices that lead to long-term results.  Short-term weight loss and long-term fat loss are two completely different things!

But this article is different.  It’s a story of rapid weight loss for a short-term goal.

You may not want to lose a ton of water weight for a UFC fight, a bodybuilding show, or a weight-based wrestling competition. 

But understanding how the body regulates weight in the different compartments will help you understand why your weight can bounce around daily and why it’s the long-term trend that really matters.   

In summary, his article will show you that you can manipulate your weight by:

  • Reducing minerals,
  • Restricting fibre, and
  • Drinking less water. 

By the end, you’ll also understand why you should do the opposite for long-term fat loss. 

The Backstory  

Not long ago, my 16-year-old son Mike—dreaming as big as teenagers do—had his eye on setting an under-18 deadlift world record. 

The catch was that he needed to be under 82.5 kilos the day before the comp!  

When he was diagnosed with Type-1 Diabetes just over a year ago, his weight had dropped to 77 kilograms (169 lbs)!  With uncontrolled T1D, someone’s body cannot stop itself from liberating its protein (muscle and organs), fat (body fat), and glucose (blood glucose and glycogen stores).  So, he lost a lot of weight in a short amount of time.  Fortunately, he quickly gained the weight back, mainly in the form of muscle. 

The photo on the left below shows Mike in the hospital when he was diagnosed.  The one on the left shows him just a few weeks after starting insulin, stronger than ever.

At an October 2022 powerlifting competition, Mike pulled 231 kilos to set an Australian under-90-kilo deadlift record.  So, he could already lift enough to get the world record of 212 kg.  He just needed to drop some weight to qualify for the lower-weight class. 

He wanted a world record pretty badly, and desperate times call for desperate measures!  So, we worked with our powerlifting coach to make it happen.  To our surprise, it didn’t end up being that hard to lose 4.5 kilos in less than 24 hours!   

The chart below shows Mike’s weight as he prepared for the competition.  Here, we can see:

  • a steady period of incremental weight loss over the long term,
  • a rapid loss of 4.5 kilos before his 81.5 kg weigh-in, and
  • regaining back several kilos to hit 87.2 kilos before he competed the following day! 

This chart zooms in on his weight loss around the final weigh-in.   

I find it both crazy and fascinating to see how someone can fluctuate 7% of their body weight in just a few hours! 

How Did He Go?

If you’re wondering how the competition went… Mike SMASHED the world record by 32 kilograms, deadlifting 245 kilos (540 lbs)!  That’s three times his body weight at weigh-in!

While fascinating, this is a ‘don’t try this at home’ story.   If you need to lose water weight quickly, you should:

  • work with someone who is knowledgeable and has plenty of experience in doing this; and
  • make sure you’re prepared to gain all the weight back shortly after. 

Nonetheless, I thought it would be fascinating to unpack the different components of weight loss—with Mike’s story woven in—so you can choose the right levers that align with your long-term goals. 

The Components of Body Weight

First, let’s look at the different components of your body that make up the weight on the scale and how you can manipulate them.  

Many people over-simplistically judge their progress by their weight on the scale.  While this has some merit, the various components of your body weight can be managed and manipulated separately, as you will see.  Let’s jump into what those are.

Body Fat

Body fat gets the most focus, and rightfully so. 

That fat on your body is your portable energy storage—kind of like a portable battery—that allows us to have enough fuel between meals or if you don’t have access to food for a while. 

A healthy body fat percentage for men is around 15% of your body weight, whereas 25% is healthy for women. 

But in our modern-day, ultra-processed, hyper-palatable food environment, most of us have a LOT more body fat than we need! 

Your body fat can safely store a lot of energy; around 1 pound (454 grams) of body fat contains about 3500 calories.  

However, there comes the point where it becomes full, like a saturated sponge that can’t take any more water.  This ‘point’, known as your Personal Fat Threshold, is critical for maintaining your health and avoiding the long list of modern diseases.

If you keep forcing energy into your body with a low-satiety, nutrient-poor diet, you will eventually have so much excess energy floating around your system that it has nowhere to go.  As a result, you will exceed your Personal Fat Threshold, and the excess energy you continue to eat on top of that will get stored in your liver, muscles, eyes, and other places it doesn’t belong. 

To try and compensate for all the energy it has to manage and keep in storage, your pancreas will continue to ramp up insulin production.  As time goes on, it will eventually tire out and lose that battle. 

Before long, this ‘excess energy’ will turn into energy toxicity—the root cause of insulin resistance, metabolic syndrome, Type-2 Diabetes, heart disease, and many other conditions that are all too prevalent today. 

That said, losing body fat is a long-term game. 

There are no quick fixes (that last).

But what you must do to get where you want to be might not be as complicated as you think; you ‘simply’ have to consume less energy than you expend over the long term so you can deplete your blood and body fat stores. 

The challenge for most people is that our appetite is tightly regulated to ensure we get the right balance of nutrients and energy we need every day.  So, if you don’t get enough nutrients in proportion to energy, your appetite will increase, and the amount of energy your body uses will reduce. 

Unless someone changes what they eat, most people fail at long-term fat loss.  Despite exerting maximum willpower, it’s challenging for your body not to respond with hunger if you simply eat less of already nutrient-poor foods.   

As we’ve discussed in other articles, the key to depleting your excess stored body fat is to change what you eat by increasing the satiety value of your diet.  By packing in more nutrients per calorie, your appetite settles down, and your body is happy to shed the excess energy you’ve stored on your body. 

If you’re interested in finding the right foods that provide greater satiety and more of the nutrients you need, you grab our optimised food list bundle.

Muscle and Organs

Your muscle and organs are the engine room of your metabolism.  They use the energy in the form of ATP your body makes from the food you eat and the fat on your body. 

As noted in the article, The Relationship Between Fat-Free Lean Mass, Energy Requirements and Macros, our calorie intake is proportional to our lean mass.  Your body fat doesn’t use energy. 

You will use and need to consume more energy if you have more muscle mass.  So, the best way to ensure you can eat more and get more nutrients is to keep your muscle mass high through resistance training. 

Often, we talk about our ‘lean mass’.  This is simply the weight of your body that is not fat, which includes water.  Water does not burn calories, so it is somewhat irrelevant.  Hence, it’s more accurate to talk about the protein stored in your body, which is the dry weight of your muscles and organs. 

If you have a bioimpedance scale, you may see a value for body protein.  For example, the snip below from my Renpho scale shows my protein % at 18.7%.   

If you start to lose lean mass—which can result from prolonged dieting, inadequate protein intake, illness, hormonal imbalance, or natural hormonal changes that occur with aging—your appetite will increase to ensure you get the protein you require to maintain your protein stores.  Unfortunately, when our appetite increases, most of us reach for the low-satiety carb-and-fat combo foods, which means we usually gain fat rather than muscle! 

Whether you’re trying to lose weight after menopause or to make weight for a competition, you want to keep your protein intake up and remain active to minimise the lean mass you’ll lose. 


Glycogen is the fancy name for the storage form of glucose. 

After any meal you consume with carbs or protein, your body starts to synthesise glycogen.  This allows your body to have an easily accessible form of fuel in between meals.

Your liver and muscle glycogen stores are never completely exhausted, even when you’re not eating.  Glycogen is continually topped up from the carbohydrates in the food you eat and through the conversion of dietary protein and bodily protein stores to glucose via gluconeogenesis

It’s interesting to note that every gram of glucose is stored with four grams of water.  So, if your glucose is elevated, you’ll also store lots of extra water with the glucose in your liver and muscles.  

So, if you’re wondering how the scale jumped so much after one day of Christmas cookies, this is your answer!  The rapid jump in your scale is not fat.  It’s mainly water that is stored with the extra glucose. 

Aside from naturally fluctuating between high and low-carb days, reducing carbs and not eating as regularly will also cause you to lose a lot of water weight as you deplete your glycogen.  Hence, it will result in weight loss. 

While it may seem like ‘magic’, this initial weight loss many people experience through extended fasting or on a low-carb, carnivore, or keto diet is what gets many people hooked on it.  This is sometimes referred to as ‘losing water weight’ and ‘the whoosh’.

While it’s not fat loss, losing some water weight is integral to the fat loss process.  Due to oxidative priority, you must deplete glucose—which is accompanied by water—before you can start chipping away at body fat.

If your blood glucose rises by more than 30 mg/dL (1.6 mmol/dL) after a meal, it might be worth lowering your carb intake until they stabilise.  However, some fluctuations in your glucose are normal and healthy, and you don’t have to cut out all carbs to make long-term progress, especially if it leads you to overdo the fat.   

Our analysis shows that the optimal carb intake for maximum satiety is 10-20% of total calories.  However, we still see a positive satiety response when we consume upwards of 50% of total calories from carbs.  In this scenario, though, someone is consuming these carbs with protein and not fat (i.e., they’re avoiding the hyper-palatable fat-and-carb combo).

But there’s no point in overfilling your glucose fuel tank.  In our Data-Driven Fasting Challenges and Macros Masterclasses, we guide people to dial back their intake of refined carbs if their glucose rises by more than 30 mg/dL (1.6 mmol/L) after eating. 

Dialling back excess carbs not only helps deplete excess stored glycogen so you can tap into your body fat, but it also helps prevent rebound hypoglycaemia.  When your glucose comes crashing down hours after overconsuming the carbs, you will find yourself hungry and more prone to making poorer food choices.   

Gut Contents

Generally, food with more fibre tends to help us eat less.  Fibrous foods also tend to contain more nutrients than highly refined and processed carbs.  This leads to greater satiety, which makes weight loss easier.   

While we don’t make a big deal of fibre in our programs, you’ll get plenty of fibre it if you prioritise less-refined nutritious foods.  For more details on fibre, see Dietary Fiber: How Much Do You Need?

While you do not need to eat as large quantities of protein or fat to get the nutrients you require, they still contribute to the mass your gut is retaining.  But because protein and fat are two of the most satiating macronutrients and because high-protein foods tend to provide an array of other satiating micronutrients, it’s crucial you’re getting some of them.

No matter what you consume, the weight of food in your gut can be significant, and every bit counts if your only goal is to reduce the number on the scale!  In the lead-up to a weigh-in, it can help to decrease fibrous foods.  During Mike’s cut, he ate boiled eggs in the last few days to reduce his gut’s contents.   

Counterintuitively, some people even use dark chocolate to get some calories with little fibre and bulk.  In the last few days, you’re not trying to lose more fat; your goal is to manipulate water weight. 

Body Water

You don’t just have water in your blood; your lymph fluid, muscles, brain, and other systems throughout your body all contain water.  The average cell is 70% water.  Your water weight is considered your ‘lean mass’. 

The normal range for body water is 50 to 65%.  The following snip from my Renpho scale shows I’m 59.1% water. 

The fact that your body is more than half water is why you can lose so much weight so quickly by manipulating your water weight.  Fortunately, your body does a good job regulating your thirst to maintain a healthy amount of water most of the time, so most people don’t need to worry too much about their water weight. 

After you’ve lost as much fat as you reasonably can and cut back on fibrous foods, the key to rapid weight loss is to drink a lot MORE water than you usually do for a few days. 

While this will cause your weight to increase for a few days, your body will respond by downregulating its production of water-retaining hormones like aldosterone and anti-diuretic hormone.  Subsequently, you’ll pee a LOT more. 

Initially, your kidneys will excrete a lot more water, and you’ll be heading to the bathroom more often.  But once you stop drinking water, your body continues to pee more than you usually do!  And voila, you’ll have rapid overnight water loss!


When you drink more water, you also flush out all your minerals.   

Insulin helps your kidneys recycle minerals.  So, after several days of low insulin levels from lowered food intake and decreased salt intake, your kidneys won’t hold onto minerals like sodium, potassium, and magnesium

This technique of over-drinking water and abruptly dialling back the water intake forces your body to become hyponatremic, which is the medical word for low sodium levels.  If you also cut your salt intake along with this, your body will flush out even more minerals and water!  Drinking diuretic beverages like black and green teas and coffee can also increase these effects. 


The final key to the weight-cutting protocol is heat.  Many UFC fighters use a sauna, but a hot bath will also do the trick.  As you heat up, you’ll sweat more, and the water inside your body will come out more quickly. 

You Feel Like Crap!

It’s important to note that, at this point, you feel awful! 

With lowered food intake, you feel weak.

With no water, you feel incredibly thirsty.

And with lowered levels of all your core electrolytes (i.e., sodium, potassium, magnesium, chloride, and potassium), you’ll feel trashy and weaker than ever!  

Electrolytes are nicknamed the ‘spark plugs of life’; they transmit nerve impulses throughout your body, contract and relax your muscles, and transport substances like glucose into your bloodstream.

UFC fighters and wrestlers who have weigh-ins the day before a fight must balance the loss of strength and cognition with making weight, hoping they can rehydrate and get their mineral balance back up quickly so they can be fit to fight. 

While UFC fighters will water cut for several days to drop as much as 10% of their body weight, it’s ideal if you can lose as much fat as possible, so you only need to cut a little water weight.  If you lose too much weight, your risk losing too much strength, not to mention mental capacity.

To keep the adverse effects to a minimum, Mike kept drinking water under the guidance of our coach Jamie until 4 pm the day before the weigh-in, which was at 2 pm the next day.  It only took 22 hours to flush 4.5 kilos of water to weigh in at 81.5 kg the day before the deadlift competition.  

Rehydration and Refeeding

After the weigh-in, it’s time to get your weight, energy, and electrolytes back up. 

What you eat the day before a competition is even more important than what you eat the day of.  Your body needs to metabolise and store all that energy and stabilise your blood glucose levels before it can perform optimally. 

You want to refill your electrolytes, glucose, and fat rapidly so you can give the best performance of your life!  Whether it be a game, marathon, fight, weight lifting comp, or a long-distance bike or swim, this holds true for any athlete preparing for a big event!

Eating too much right before the competition will leave your gut stuck in overdrive digesting.  Instead of setting a new PR, you’ll want to lay down in the corner for a nap!  Hence, you want your blood and glycogen stores to be full of nutrients and energy so they can keep feeding your muscles; you don’t want them sitting in your gut waiting to be digested! 

Additionally, trying to eat a lot right before an event can leave you on the blood sugar rollercoaster, with your blood sugar rising and crashing shortly after.  Subsequently, you may not feel great or have enough glucose available for your event.

So, your goal should be to finish refeeding the day before your event after your weigh-in so you can eat normally on the day of. 

After dieting for weeks or months and restricting minerals and water for those few days, your appetite will be in overdrive once you let it loose to bring your levels back to normal.  At this point, it’s essential to prioritise sodium along with potassium and magnesium

This is the perfect time to replenish your energy stores quickly for those low-satiety, low-protein, low-fibre, carb-and-fat combo foods and meals that we usually advise against.  This is because these foods allow you to eat a LOT without feeling too full, and they fill up your carb and fat fuel tanks relatively quickly.  


So, to summarise, there are several components to rapid weight cutting:

  • Fat loss.  Like any normal diet, this is a long-term endeavour that you should anticipate several weeks to months in advance, depending on your goals.
  • Muscle/lean mass.  Similar to any standard diet method, you want to ensure you get adequate protein, which will minimise the amount of muscle you lose.
  • Glycogen.  Minimising or eliminating carbs 2-3 days in advance will allow your body to reduce its glycogen stores, which are 80% water.
  • Gut contents.  Cutting back on fibre and other bulky foods that absorb water (i.e., grains) will help reduce the weight of food sitting in the gut.
  • Water.  While it may seem counterintuitive, we can force the body to excrete more water by drinking more water and then abruptly cutting back.   
  • Electrolytes.  Minerals balance body water levels.  Hence, decreasing your consumption of core minerals like sodium, potassium, magnesium, calcium, and chloride helps the body flush more water. 

It’s important to mention again that this approach is only helpful for short-term weight loss.  Applying one or even all of these principles for too long may end in severe consequences and can even cause rebound weight gain in the long term.  

If you’re looking to lose weight successfully over the long term and keep it off, you might check out our Macros Masterclass or Data-Driven Fasting Challenges, which teach Optimisers how to balance dieting and maintenance to ensure consistent and sustainable results.

Mike’s N=1

To allow you to picture what this might look like in real life, I thought it might be interesting to look at Mike’s n=1 journey.

Fat-Loss Phase

After Mike finished rugby and his previous powerlifting competition—two events that required him to eat more—he started watching his calories and tracking in Cronometer most days.  I set him up with a target of 2000 calories per day with:

  • 220 grams of protein (49% total calories),
  • 50 grams of net carbs (11% total calories), and
  • 100 grams of fat (40% total calories). 

These macros were great for controlling his Type-1 DiabetesProtein is excellent for maximising satiety so you can lose weight over the long term, and it is vital for stabilising and even dropping blood glucose.  You only need to go higher than 50% protein when things get desperate.  

Mike didn’t adhere to these macros ‘perfectly’ according to plan every day; he had a number of exams and assignments due, so he just ate normally to ensure his brain could still function well. 

It was fascinating to see how Mike hardly needed any insulin to keep his blood sugar stable and in the normal range on days stuck to his calorie deficit! 

Over five weeks, he lost about 0.8% of his body weight per week, which is a nice healthy rate of loss. 

A week and a half before the comp, Jamie said that was enough fat loss and that he needed to maintain his strength for the comp.  So, Mike transitioned back to eating normally so he could ensure he maintained as much muscle and power for the big day.

Water Loading

Mike increased his water intake to about seven litres daily six days before the weigh-in.  At first, it was hard to drink that much water.  But after a few days, his body adjusted.

Decreasing His Intake of Fibre, Carbs, and Salt

The day before weigh-in, Mike dropped his fibre and carbs, which were already pretty low.  This left him with a lot of protein—like hard-boiled eggs, which we mentioned earlier—and water.  He also avoided salt for the day.

Stop Drinking!

The day before the weigh-in, Mike dropped his water intake to 5 litres of water that day.  He stopped drinking at 6 pm the night before, too.  The chart below shows Mike’s 4.5 kg weight loss in just over 12 hours! 


Coffee can work as a diuretic, making your body flush out water.  So, Mike had an espresso coffee on the morning of the weigh-in.  

Heat and Sweat

Many people use saunas to shed water weight, but a hot bath does the same job and is often more accessible.  Boxers and UFC fighters use sweat suits but are somewhat extreme and deplete energy levels even more.

Mike had his first hot bath four hours before his weigh-in, which made his weight drop rapidly.  After that, he went for a walk in hi 

From there, it was time to go to his weigh-in.  We then drove into the gym with the air turned up to high heat, which helped him sweat out a bit more water. 

We were super pleased to see that when he finally weighed in, he was one kilo under his goal weight!

Rehydration and Refeeding

Immediately after weighing in, Mike was already downing some water and electrolytes.  We then went out for some food, where everything and anything we knew about nutrient density went out the window.   Let’s just say the satiety values weren’t too high!

Learn More

Cutting weight is something bodybuilders, wrestlers, weight lifters, and fighters use to make weight before a competition.  Bodybuilders use it to gain more definition, whereas other athletes use it to fall into a weight class they want to compete in.

If you want to learn more about the science behind all this, I recommend reading The Effect of Water Loading on Acute Weight Loss Following Fluid Restriction in Combat Sports Athletes by Reid Reale and colleagues and this podcast with Reid and Danny Lennon on Sigma Nutrition Radio

This was a surprisingly easy process under the wise guidance of Jamie, who has plenty of knowledge and experience in this discipline.  

This was Mike’s first and perhaps only weight cut, which also likely made the process easier; as you try and restrict calories more often with a greater calorie deficit, your body is likely to be less responsive and can even retaliate by gaining weight over the long term.

I just wanted to take a minute and say one more time, don’t try this on your own!  It can be a miserable experience because it’s not healthy!   

Implications for Long-Term Fat Loss

To wrap this up, I want to highlight some of the points that make this knowledge relevant for the rest of us who want to lose body fat and improve our metabolic health. 

Fat Loss Is a Long-Term Game!  Ignore Short-Term Fluctuations

Hopefully, this n=1 has shown that water weight, and thus your weight on the scale, can fluctuate wildly.  There is a wide range of things that can contribute to short-term fluctuations on the scale that can lead people to become discouraged, like:

  • Water intake,
  • Fibre intake,
  • Electrolytes,
  • Exercise, and
  • Monthly hormonal changes for women. 

Rather than stressing over the short day-to-day blips on the scale, you should keep an eye on your weight over the longer term, like weekly or monthly for females.  Looking at these trends is way more meaningful than those we see daily, and it messes with your mind a lot less! 

As discussed in How Much Weight Should I Lose Per Week?, you’re doing great if you lose 0.5 to 1.0% of your starting body weight per week.  Pushing harder will only risk excessive hunger, losing precious lean muscle mass, and rebound binging. 

Water Intake

As a general rule, you should drink to thirst.  Your body and kidneys know how much water you need, and they will send you in search of more if you’re getting low. 

The colour of your urine is also a great indication of the amount of water you need.  If it is thoroughly yellow, dark yellow, or even brown, it likely means you need more water.  In contrast, clear yellow can indicate overhydration or the need for more vitamins and minerals.

While you should err on the side of caution and drink more than less, forcing yourself to overdrink can lead to a loss of precious minerals. 

Nutrient-dense foods tend to have a lower energy density and naturally contain a ton of water and fibre, so you can get plenty of water from the food you’re eating. 

Carbohydrate and Blood Glucose

Reducing carbs helps reduce water weight.  However, if you’re still consuming a lot of fat in your diet, you may still have a ton of excess body fat. 

It is intelligent to reduce carbs to achieve normal and healthy blood sugar variability.  Not only will this help you reduce water weight, but it will also help you look less inflamed. 

Once you deplete the stored glucose in your body, you can get on with using your body fat for fuel, so long as you aren’t overconsuming dietary fat.

Mineral Intake Critical for Hydration

Our satiety analysis has shown that minerals like sodium, potassium, and calcium play a critical role in satiety.  Therefore, we will seek out more food to get them if our diet contains less of them.

Having adequate minerals in your diet ensures your kidneys don’t have to work too hard to recycle the precious minerals that you’re getting from your diet; your body needs a particular ratio of sodium, potassium, calcium, magnesium, chloride, and water to perform a long list of day-to-day functions.

Sodium and potassium are your key fluid-balancing minerals.  While sodium, calcium, and chloride function as extracellular minerals that maintain fluid balance outside of cells (i.e., extracellular minerals), potassium and magnesium function as intracellular minerals, maintaining fluid balance inside cells.  

So, if you consume adequate potassium and sodium, your body can more easily regulate the water inside and outside your cells. 

Fibre and Energy Density

Nutrient-dense foods contain more fibre and have a lower energy density because they naturally contain more water.  Fibre and low-energy-density foods will help you feel fuller, especially in the short term.  They also have a lot of vitamins and minerals, which positively influence satiety and support longer-term fat loss. 


While you can manipulate water weight in the short term, it’s not ideal for long-term health or weight loss. 

To maximise your long-term health and fat loss: