84 Hours (The Full Reset)

I just completed an 84-hour fast: Sunday at 7pm to Thursday morning at 7am. I wanted to share what I did, what I learned the second time around, and what I’ll do differently next time.

This past year has shown me that the mind leads and the body follows. Commit fully to what you believe and the body will find a way to get there. This fast was just the latest proof of that.

It was actually my previous Coach Joe Tewell, who first suggested I try an extended fast. That conversation planted the seed. Last August I completed a 60-hour fast as my first attempt, and this time I wanted to push a little further.

Everything I’m sharing here is based on my personal experience and information I’ve researched and verified. I’m not a doctor and this is not medical advice.

For anyone wondering why 84 hours, those three and a half days give the body enough time to burn through stored glycogen (the form of sugar stored in muscles and the liver as a quick energy reserve) then shift fully into fat burning and trigger deeper cellular cleanup. Short fasts help, but a few days allow the full process to run its course. I view it as a full reset for the system, not just a quick restart.

The protocol I ran

7:00 AM — LMNT w/ 24 oz water
9:00 AM — BCAA 5000 w/ 16 oz water
12:00 PM — LMNT w/ 24 oz water
3:00 PM — BCAA 5000 w/ 16 oz water
5:00 PM — LMNT w/ 24 oz water
9:00 PM — BCAA 5000 w/ 16 oz water (Monday & Tuesday only, I trained those evenings. Wednesday was a rest day, so I skipped this dose.)

The protocol alone accounted for 104 oz of water per day on Monday & Tuesday, and 88 oz on Wednesday since I skipped the evening BCAA dose on my rest day. On top of that I drank another 16–20 oz throughout the day, bringing my total intake to roughly 120 oz on active days and around 104 oz on Wednesday.

LMNT is an electrolyte mix of sodium, potassium, and magnesium, which helps keep energy stable and prevents the fatigue that often derails longer fasts.

BCAA 5000 is a branched-chain amino acid supplement that signals the body to preserve muscle instead of breaking it down for fuel.

The electrolytes helped keep fatigue in check, the BCAAs supported muscle preservation, and I made sure to keep my heart rate under 125 BPM throughout.

Daily step count

Sunday — 20,166 (day leading into the fast)
Monday — 21,255
Tuesday — 17,078
Wednesday — 15,917

I received my RMR (resting metabolic rate) results on Tuesday which helped me determine that 15,000 steps is a better daily target for me going forward. Wednesday’s count reflects that adjustment and the intentional ramp down on my rest day.

Throughout the entire fast I continued my normal workout routine and maintained my daily step count as close to target as possible. Outside of not eating, nothing changed. Same training, same movement, same schedule. The goal was to treat the fast as a tool, not a reason to shut everything else down.

One thing worth mentioning (sleep)

Sleep during a fast is one of the most important windows for recovery. The body performs significant repair work overnight, and those hours count toward your fasting window. Prioritizing sleep during an extended fast isn’t optional. It’s part of the protocol. Although most professionals recommend 7–9 hours of sleep during an extended fast, I averaged 7 hours and 14 minutes per night throughout, just above the minimum of the recommended range. Next time I’ll aim for 8 and see if there’s a noticeable difference in how I feel and recover. The more quality sleep you get during the fast, the more repair work the body can do overnight.

What’s happening to your body during the fast

The process happens in stages.

0–24 hours: The body burns through stored glucose, the sugar stored in muscles and the liver for quick energy. Once that runs out, insulin drops and the body begins shifting to fat for fuel. That drop unlocks stored fat from adipose tissue, essentially the fat the body has been holding in reserve, and begins converting it into ketones in the liver. Ketones are an alternative fuel source the brain and muscles can run on in the absence of glucose.

24–48 hours: You enter full ketosis, a metabolic state where the body has fully switched from burning glucose to burning fat for fuel, producing ketones as its primary energy source. Ketones become a primary fuel source for the brain and muscles. Autophagy begins, think of it as the body’s internal maintenance crew, breaking down damaged cellular components and recycling them.

48–72 hours: Autophagy deepens. Inflammation markers begin to drop. Growth hormone rises, a hormone that supports muscle preservation and repair, helping protect the muscle tissue you’ve built.

72–84 hours: This is the deepest stage of the fast. Ketones peak and cellular repair is at its highest level.

Day one clears the runway by burning stored fuel. Everything after that is where the real work begins. Repair, cleanup, and rebuilding.

One thing that held true from my first fast and continued through this one was my energy levels. Even on the days I trained I didn’t experience the dips most people expect. No crashes, no wall. Glucose creates energy spikes and crashes because blood sugar fluctuates depending on what and when you eat. Ketones are produced at a steadier rate from fat stores and don’t cause the same rapid rises and falls. The result is a more consistent energy supply to the brain and muscles, and you feel it.

What the latest science says

A 2024 study published in Nature Metabolism out of Queen Mary University of London found that after 72 hours of fasting the body begins a coordinated transformation across multiple organs, affecting thousands of proteins simultaneously. The changes go well beyond fat burning, researchers described it as the body potentially reorganizing itself at a biological level. While more research is needed to fully understand the implications, it’s one of the most significant studies to date mapping the full body response to extended fasting and it adds serious scientific weight to why the 72-plus hour window matters.

A note on the protocol I chose

Most fasting professionals recommend keeping it straightforward, water and electrolytes only. That’s the standard baseline and a completely valid approach. Where opinions differ is on BCAAs. Some practitioners support them during a fast specifically for muscle preservation, especially if you’re training. Others argue that any amino acid intake technically interrupts a true fast because it can trigger a small insulin response and slightly reduce autophagy. I chose to include BCAAs because preserving the muscle I spent the past year building was a priority for me. That’s a personal decision based on my goals and where I am in my training. It’s not the only way to approach it, and it may not be the right choice for everyone. If you’re thinking about trying an extended fast, do your research, talk to your coach, and build a protocol that fits your goals, not just mine.

For anyone curious about trying it

Science is real, and if I can help someone do it the right way I’m happy to share what worked for me. The minimum where you start seeing meaningful benefits is about 24 hours. That’s when fat burning begins and cellular cleanup processes start to activate. The maximum without medical supervision is generally considered around 120 hours (five days). Beyond that the benefits plateau and refeeding becomes more complicated. Most professionals recommend doing extended fasts two to four times per year. I personally plan to do them three times a year. Think of it as a practice, not a one-time event.

Important note

Extended fasting is not for everyone. Anyone who has diabetes, takes medications, has a history of disordered eating, or is pregnant should consult a doctor before attempting it. This is a tool for healthy individuals who are ready to approach it with structure and intention. When in doubt, talk to your doctor first.

What professionals generally recommend for breaking a fast

Most professionals suggest easing back into food after an extended fast rather than jumping straight into a full meal. The typical approach is to start with liquids first. Bone broth is often considered the gold standard because it’s gentle on the digestive system, replaces electrolytes, and helps prepare the gut after several days without food.

For the first meal, many practitioners suggest combining a few soft, easily digestible foods. Eggs are commonly included because they provide high-quality protein and are easy on the stomach. Avocado is another frequent addition since it supplies healthy fats and potassium, which helps restore electrolytes. Cooked vegetables are sometimes included as well because they’re easier to digest than raw vegetables.

From there, the next meal can introduce lean protein and simple carbohydrates. Chicken, fish, rice, and cooked potatoes are often used because they help restore glycogen without overwhelming digestion.

By the evening meal the digestive system is usually more active again, and a fuller whole-food meal becomes appropriate. Anything heavier or more complex is typically better saved for day two once digestion is fully back online.

The goal throughout the entire refeed day is simply to wake the digestive system back up gradually rather than shocking it with a large meal.

What I did

It is generally suggested to space meals roughly 4–6 hours apart on the first refeed day to give the digestive system time to wake back up gradually. These were the times I chose to follow.

7:00am — 16 oz bone broth, 2 soft-boiled eggs, half avocado

For anyone wondering how to make soft-boiled eggs, I was too:

Bring water to a boil. Gently lower the eggs in with a spoon. Set your timer,6 minutes for a runny yolk, 6½ minutes for slightly thicker which is what I went with, 7 minutes for a jammy yolk. Transfer immediately to ice water for 1 minute to stop the cooking. Peel and serve.

12:30pm — 160g chicken breast, 170g basmati rice, 100g cooked vegetables, 5g olive oil

6:00pm — 150g salmon, 180g baby potatoes, 100g cooked vegetables, 5g olive oil or butter

A note on the olive oil, it wasn’t just for flavor. Fat helps the body absorb fat-soluble vitamins present in vegetables, and it slows digestion slightly which helps stabilize blood sugar after a fast when insulin sensitivity is heightened. Five grams is a small enough amount that it won’t overwhelm the digestive system on day one but still provides those benefits.

Even if you feel great, don’t rush portions or add extra snacks on day one. The goal is to let digestion ramp back up gradually. By day two you can return to a normal eating schedule.

Liquid first. Light whole foods next. Full meal by the end of the day.

The fast was the work. The refeed is part of the process. Respect both.

What surprised me

Many people assume extended fasting means you’ll feel miserable and starving the entire time. That wasn’t my experience. The first 24 hours I felt hunger, mostly because the body is still signaling on its normal meal schedule. I’ll be honest, smelling my wife’s cooking didn’t help. She cooks every day and day one that was a real test. But after that first day the hunger largely disappeared and so did the distraction. What used to trigger it simply stopped affecting me.

Hunger is heavily driven by a hormone called ghrelin, the body’s primary hunger signal, which spikes around normal meal times. Once the body adjusts, those signals stabilize. Most people, myself included, report that by day two the hunger fades and gets replaced by steady energy and mental clarity. That’s the ketones at work.

Why fasting sharpens the mind

Under normal circumstances the brain runs almost exclusively on glucose. When you fast long enough and shift into ketosis the brain starts running on ketones instead. Ketones are a cleaner and more stable fuel source than glucose. They don’t cause the same spikes and crashes that come with eating throughout the day. The result is reduced brain fog, sharper focus, and a sense of calm mental clarity that most people don’t expect going into an extended fast. There’s real neuroscience behind it, researchers are actually studying ketones as a therapeutic tool for neurological conditions for this reason. There’s also a secondary factor. Without the work of digesting food the body redirects energy that would normally go toward digestion. That freed up energy contributes to the mental sharpness as well. It’s one of the more surprising benefits of an extended fast and one of the reasons people who do it once tend to do it again. Fasting also increases levels of a protein called BDNF, a brain protein that supports neuron health and is associated with improved learning, focus, and mental resilience. It’s one of the reasons the mental sharpness during an extended fast isn’t just a feeling. There’s biology behind it.

One thing nobody warns you about

You’ll be making a lot more trips to the bathroom than usual and it doesn’t just happen in the first day or two. It continues throughout the entire fast. To be clear, this is primarily urination, not trips for any other reason. As the body burns glycogen it releases the water stored with it. When insulin drops this low, the kidneys also excrete more sodium and water. That’s exactly why electrolytes become a non-negotiable part of the protocol. On the other end, bowel movements decrease significantly and typically stop almost entirely after the first day or two. With no food moving through the digestive system there is simply nothing to process. This is completely normal and expected. With roughly 104–120 oz of water daily, the body is essentially flushing continuously. It’s not a problem, so don’t be alarmed, it’s part of the process.

One more thing worth mentioning

Shortly after eating my first meal to break the fast, I noticed a slight tingling sensation throughout my body. Nothing uncomfortable, just something I hadn’t experienced after my previous shorter fast. From what I’ve read, that’s not unusual after a longer fast. When insulin turns back on and nutrients start moving into cells again, the body can react to that shift. Others who have completed extended fasts report similar experiences, mild tingling, a brief warmth, or a light buzzing sensation shortly after that first meal. For me it passed within a short period of time. It’s considered a normal refeeding response and not something to be alarmed about. Not everyone will feel it, but it’s something worth knowing about so you’re not caught off guard if it happens.

A little later I also experienced some mild light-headedness and very light heart palpitations. These resolved fairly quickly after hydrating and replenishing electrolytes. Extended fasting changes fluid balance, blood pressure, and electrolyte levels, so as the body transitions back into a fed state it’s possible to feel some temporary shifts. It’s another reminder that longer fasts should be approached carefully, with attention to hydration, electrolytes, and how the body is responding. If palpitations are strong, prolonged, or accompanied by chest pain or shortness of breath, stop and seek medical attention immediately. What I experienced was mild and brief but knowing the difference matters.

Another thing worth mentioning is the digestive response when refeeding. After my first meal I experienced a brief episode of diarrhea. From what I’ve learned, that can happen when breaking a longer fast. During several days without food the digestive system slows down and gut activity changes. When food is reintroduced, the system can briefly over-react as enzymes, bile flow, and gut motility restart. For me it resolved quickly once I rehydrated and replenished electrolytes. Like the other symptoms I mentioned, it was short-lived, but it’s something people should be aware of so they don’t assume something is wrong if it happens.

One thing I didn’t do but will next time

This is something I learned after the fact and wanted to pass along. What you eat in the one to two days before your fast matters more than most people realize. I went into my first fast as well as this fast without any real preparation on the eating side. Starting a fast after two days of clean low-carb eating can speed up your shift into ketosis significantly and make day one considerably easier.

Here’s the approach: Two days before, clean up your eating. Cut out sugar, alcohol, processed foods, and heavy carbs. Focus on protein, healthy fats, and vegetables. Then the day before, tighten it further. Your last meal before the fast should be protein, healthy fats, and non-starchy vegetables with minimal carbs. Think salmon or chicken, avocado, leafy greens, broccoli. Skip the bread, pasta, rice, and anything sugary for that last meal. The goal is to enter the fast with blood sugar stable and the body already trending toward fat burning before the fast even begins. I now understand why it matters and it’s the first thing I’ll do differently next time.

Weight data

One thing I want to be clear about, weight loss was not the goal of this fast, and it should not be the reason anyone attempts one. The numbers you see here are a byproduct of the process, not the point. Extended fasting is a tool for cellular repair, metabolic reset, and inflammation reduction. If someone is considering this primarily as a weight loss strategy, there are far better and more sustainable approaches. This is not a diet. It’s a practice with a specific purpose.

April 5 — 161.6 lbs  (7:04am, morning of the fast that started at 7pm)
April 6 — 160.9 lbs  7:05am
April 7 — 158.8 lbs  7:03am
April 8 — 156.5 lbs  7:01am
April 9 — 155.4 lbs  6:59am

Total drop over the fast: 6.2 lbs

A few pounds of that initial drop is water weight and glycogen, which is expected and will partially return once I refeed. That’s not the goal of the fast anyway. The real work is happening at the cellular level.

The scale is just one data point.

My next fast will be 108 hours. Earlier in this post we noted that 120 hours (five days) is generally considered the maximum for extended fasting without physician supervision. At 108 hours I stay inside that boundary while pushing a little further than this one. Most practitioners suggest building up progressively, starting with shorter fasting windows and adding time only after the body has adapted to each stage. That’s the approach I’ve followed going from 60 to 84 to 108. Build it, don’t jump it.

Discipline builds the structure. The body simply responds. Reset the body. Sharpen the mind. Show up better. That’s the whole point.

84 Hours (The Full Reset)
A Reflection by Alexander Bush
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