u/andtitov

Hi folks! I see so many posts on electrolytes for extended fasting, so I want to reshare my previous post on this topic. Basically, electrolytes are essential for basic body function - they help prevent headaches, dizziness, low energy, and poor sleep. So, don't disregard them, and it's not that difficult to calculate your electrolyte needs during fasting

• Focus on 3 main ones - sodium, potassium and magnesium. Daily sodium needs are 3,000-5,000 mg, potassium - 1,000-2,000 mg, and magnesium - 300-400 mg. You may see lower recommendations in research as most studies focus on 12-24 hour fasting or intermittent protocols, and those targets are for safety and deficiency prevention, not performance or symptom control.
• Most electrolyte mixes are not designed for fasting. They target post-workout recovery, so many contain 30-50 calories - not acceptable for fasting.
• Ranking changes depending on whether you include all 3 minerals or just potassium and magnesium (and sodium separately through salt). The tables above for all 3 electrolytes and for only potassium+magnesium.

My personal approach is to get sodium from pink salt, so I focus on potassium and magnesium. I hope it helps. Your thoughts and ideas are welcome, and share what you use - interesting to compare.

Hey immortalists! Heart health is critical for performance and longevity as problems related to heart and blood vessel health cause about 1/3 of all deaths. So, I thought it might be interesting to share how my heart health biomarkers changed during my 10-day water fast and about a month later, after full refeeding.

Briefly, fasting had a strong positive effect on my heart health markers after refeeding, though it created a short-term dip during the fast. During the fast, many markers were off. Once I refed and stabilized, everything bounced back.

• ApoB: 136 (High) → 87 (Optimized)
• LDL Cholesterol: 161 (High) → 117 (Borderline)
• Total Cholesterol: 242 (High) → 201 (Borderline)
• Triglycerides: 163 (Borderline) → 44 (Optimized)
• HDL Cholesterol: 50 (Normal) → 71 (Optimized)
• hsCRP: 0.2 (Optimized) → 0.3 (Optimized)
• Overall Heart Health Score: 54 (Fair) → 92 (Optimal)

If you’re wondering why my ApoB and LDL spiked, basically here’s how it works. During fasting, the body switches to fat metabolism - fat gets mobilized, and LDL particles carry that fat around the body for fuel. Same thing happens during IF and a steady calorie deficit, when the body burns fat for fuel. It’s a feature, not a bug 😊 Once you refeed and stabilize, lipid transport normalizes. Triglycerides drop, HDL rises, and ApoB falls right back down.

If you tested your cardiovascular markers during fasting or a major lifestyle change, please share your results. It would be interesting to compare.

Hey folks! I’ve seen some comments saying that extended fasting crashes metabolic rate - that’s not really the case. Yes, RMR does go down during extended fasts, but the drop is usually modest. Here is my personal data. During my last 10-day fast, my RMR decreased by just over 4% - from 1,673 to 1,599 - and then returned to baseline during the refeeding period.

Just sharing my experience to address some of the concerns around metabolic rate. If you measured your metabolic rate over time, please share your results. It will be interesting to compare them.

Hey folks! I’ve been researching how extended fasting affects the brain, and one of my (surprising) takeaways is that the brain may be one of the biggest beneficiaries during prolonged fasting.

After roughly 48-72 hours of fasting, the brain gradually shifts from glucose toward ketones as a major fuel source. Ketones may provide up to 50-75% of the brain’s energy during prolonged fasting.

From the research I reviewed, extended fasting offers these 10 benefits

• Reduces neuroinflammation - through lower inflammatory cytokines and ketone signaling
• Improves brain energy stability - because ketones provide a steadier fuel source than glucose
• Increases mental clarity and focus - through stable energy, higher norepinephrine, and lower glucose swings
• Increases BDNF and neuroplasticity - helping neurons adapt and form stronger connections
• Activates deeper autophagy pathways - recycling damaged proteins and cellular components
• Reduces oxidative stress - because ketones produce fewer reactive oxygen species
• Improves mood and emotional stability - through reduced inflammation and more stable neurotransmitter signaling
• Improves gut-brain signaling - through changes in gut inflammation and microbiome activity
• Improves stress resilience - through nervous system adaptation and improved parasympathetic tone
• Supports long-term neuroprotection - through improved mitochondrial health and removal of damaged cellular material

So if you experience steadier focus, clearer thinking, calmer mood, or reduced brain fog around days 3-5 of a fast, don't get surprised - there are actual biological mechanisms behind that. At the same time, as you might know, extended fasting also carries risks such as electrolyte imbalance, sleep disruption, excessive cortisol response and others, especially as duration increases.

Curious what mental changes others here noticed during extended fasts.

Hey folks! Since keeping body fat low while preserving lean mass is critical for long-term health, I wanted to share my real body composition data from a 10-day fast followed by a 12-day refeed (I used Dexa scan to get this data)

• Total mass: 165.1 → 151.1 → 160.4 lbs
• Lean tissue: 134.1 → 125.8 → 133.8 (lost 8.3, regained 8.0)
• Fat tissue: 23.9 → 18.4 → 19.7 (lost 5.5, regained 1.3)
• Bone mineral: 7.0 → 6.9 → 6.9

So, lean mass dropped during the fast, which is expected, but nearly all of it came back during refeeding. Fat mass dropped and only partially returned. I hope this helps provide some perspective on extended fasting. If you had a chance to recoed your body recomposition data, please share, it will be cool to compare results.

Hey folks! Since I built the extended fasting weight loss calculator, I got a lot of requests to build an intermittent fasting calculator too. So it took me some time to put all my thoughts together and finally created one. A couple important points

• This calculator is basically a weight loss calculator built around a calorie deficit. IF itself does not automatically cause weight loss - it’s just an eating pattern. To lose weight, you still need a calorie deficit. That said, a good fasting windows is critical to lower blood sugar and insulin levels, so the body to access stored fat
• This calculator estimates changes in body fat, lean mass, and body composition over time based on physiology and energy balance
• Please note that the extended fasting calculator is designed for multi-day fasting with no food intake (no calories), while this calculator is focused on sustainable calorie deficits during IF, OMAD, time-restricted eating, or regular dieting.
• Weight loss during intermittent fasting is also much less predictable than during extended fasting. Accurate calorie intake, calorie expenditure, metabolic adaptation, activity levels, insulin sensitivity, water retention, and food tracking errors all affect the results.

Still, I hope this calculator gives you a good idea of what your weight loss may look like if you consistently maintain a calorie deficit.

Try it with your own numbers and share your feedback - it help me improve the calculator. Thank you in advance!

Sorry, forgot to add the link, here we go 😊

https://fasting.center/weight-loss-calculator

Hey folks! The most common feedback I got was to increase the fasting calculator beyond 40 days. Originally, I thought no one was really interested in 40+ day fasts, but it turns out I was wrong. So, I updated it - the calculator now supports fasts up to 80 days, which at least gives you projected weight loss estimates for longer fasts.

A couple important limitations to keep in mind

• One major limitation is essential body fat. Essential fat is roughly 3-5% for men and 10-13% for women. As the body approaches those levels, the risk of destructive starvation rises significantly. Right now, the calculator does not account for those physiological limits and will not warn you that a fast may be unsafe beyond a certain point.
• Another limitation that affects accuracy is water retention before the fast. Factors like inflammation, glycogen stores, insulin levels, sodium intake, stress, and hormones can all cause the body to hold extra water. During fasting - especially in the first few days - a significant amount of that water may be lost, making total weight loss appear much larger. But there’s no simple or reliable way to estimate how much extra water someone is carrying at the start.

I also got a question on the calculator accuracy. I think it’s about as accurate as it can realistically be 😊 I applied as much scientific research as I could find when building this calculator. And I’d say I’m quite good both in research (I have a PhD in Engineering and studied at MIT) and in the technical side since I work in tech.

https://fasting.center/fasting-weight-loss-calculator

I hope it helps! And as always, your feedback is welcome.

Hey folks! As you might know, resting heart rate and heart rate variability are indicators of cardiovascular fitness and autonomic nervous system balance. So, I wanted to share what happened to my RHR and HRV during my last 10-day water fast.

Basically, both improved a lot around day 5-6, then started to decline closer to the end of the fast. After I broke the fast and went back to the gym, they dropped even more - looks like I pushed too hard too soon 😊

One point - during extended fasts, cortisol goes up, which makes it harder to fall asleep and stay asleep. So, you need to actively support sleep and relaxation. Though, as you can see, the body appreciates the effort. I wish everyone would consider incorporating some type of fasting - IF, short-term fasts, or extended fasts - into their routine to give the cardiovascular system a real physiological reset.

If you have a good protocol to improve RHR and HRV, please share it. It would be interesting to learn different approaches.

Hey folks! As you might know, I’m big on fasting and wanted to share how my blood biomarker categories changed during extended fasts. In short, extended fasting temporarily lowers many biomarkers because it’s a major stressor, but they return to baseline - and often improve - after refeeding.

So, I used InsideTracker’s biomarker categories, which combine 50+ markers into 10 health areas like Heart Health, Hormone Health, Inflammation and others. Each category gets a 0-100 score (100 = best) based on how close each marker is to its ideal range. For example, Heart Health includes ApoB, TSH, hsCRP, triglycerides, HDL, LDL, total cholesterol, and resting heart rate. So here are how my biomarkers changed over the 10 months - from Dec 2024 (before my 9- and 10-day water fasts) to Oct 2025 (after complete refeeding)

• Heart Health: 76 (pre-fast) -> 54 (fast) -> 92 (refeeding)
• Fitness: 87 -> 63 -> 85
• Metabolism: 78 -> 65 -> 90
• Inflammation: 84 -> 76 -> 95
• Sleep: 81 -> 75 -> 84
• Hormone Balance: 90 -> 81 -> 94
• Cognition: 87 -> 78 -> 90
• Gut Health: 93 -> 77 -> 94
• Endurance: 86 -> 84 -> 86
• Recovery: 94 -> 90 -> 98

And, in the chart, the black line shows Dec 2024, before my fasts, the red line marks the end of my last 10-day fast in Sep 2025, and the green line shows last month, after a month of refeeding. As you can see, the red line reflects how the body feels during extended fasting - not exactly thrilled, since fasting is a stressor.

Of course, this is N=1 data, and fasting (especially extended fasting) isn’t for everyone. But for me, it helped improve 8 out of 10 biomarker categories, so I just wanted to share my experience in case it’s helpful or interesting to others. If you did blood tests during extended fasts and after, please share your results.

Hey folks! I was reviewing my fasting data and decided to visualize it. Since many people in this community are interested in extended fasting, I wanted to share it here.

These are high-level estimates based on my energy needs during the steady-state phase of extended fasts (day 4 and later) - around 2,700 calories per day. Most of the energy comes from body fat. The majority stays as fatty acids and is used primarily by muscles. Some of it is converted into ketones to fuel the brain and heart. At the same time, the body still needs glucose to support the brain and red blood cells, so it produces it from glycerol, lactate, and amino acids - since glycerol and lactate alone are not enough.

It’s not exact, just my best estimate, but I hope this chart gives a clear picture of where the energy comes from and how it’s distributed.

Hi folks! Most people think ketones are just an alternative energy source during fasting. That’s only part of the story. Yes, the liver converts roughly 20-30% of free fatty acids into ketones to help fuel the brain when glucose is low. But ketones are a powerful biohack - they are signaling molecules that actively change how your body works. Here’s what they do

• Suppress inflammation: Beta-hydroxybutyrate inhibits the NLRP3 inflammasome - a key driver of chronic inflammation
• Regulate gene expression: Ketones act as HDAC inhibitors, influencing which genes are turned on or off, including stress resistance and longevity-related pathways
• Increase cellular stress resistance: They upregulate FOXO and Nrf2 pathways, improving antioxidant defenses and resilience to damage
• Improve mitochondrial function: More efficient energy production with potentially lower oxidative stress
• Support brain function: Ketones increase BDNF and provide a stable fuel source, supporting cognition and neuroprotection
• Reduce oxidative stress: Lower ROS production compared to high-glucose metabolism states

The most efficient way to raise ketones is extended fasting. Attached is my ketone data from a 10-day water fast - ketones crossed 5 mmol/L in about 56 hours and stayed in the 5-8 mmol/L range for most of the fast.

So, fasting is not just about weight or fat loss. It’s a systemic metabolic biohack that can impact inflammation, brain function, and cellular stress responses. So, make sure that fasting as one of the tools in your health toolbox. If you’ve tracked ketones during extended fasting or keto, share your data. It will be interesting to compare results!

Written by human, edited by AI

Hi folks! Electrolytes are critical during fasting, especially extended fasting, so I wanted to share my thoughts and ranking of the ones I found on Amazon. Let's start with my thoughts

• Electrolytes are essential for basic body function - they help prevent headaches, dizziness, low energy, and poor sleep. On regular days you get them from food and drinks. During fasting, you need to supplement them.
• Focus on 3 main ones - sodium, potassium, and magnesium. Needs shift during fasting - sodium (3,000-5,000 mg) should go up, potassium (1,000-2,000 mg) stays lower. You may see lower recommendations in research - most studies focus on 12-24 hour fasting or intermittent protocols, and those targets are for safety and deficiency prevention, not performance or symptom control.
• Most electrolyte mixes are not designed for fasting. They target post-workout recovery, so many contain 30-50 calories - not acceptable for fasting.
• Ranking changes depending on whether you include all 3 minerals or just potassium and magnesium. My personal approach is to get sodium from pink salt, so I focus on potassium and magnesium.

Personally, I use Ultima - I am trying to be careful with potassium and find their packets pretty convenient. I hope it helps. Your thoughts and ideas are welcome, and share what you use - interesting to compare.

Hey folks! I know a lot of people start fasting on Monday, so I wanted to share again my list of 20 things that help me get through them - from preparation to what to do during the fast.

One suggestion - spending some quality time before or at the beginning of the fast to plan things out really helps. Think about how you’ll stay away from food, how you’ll keep yourself busy, how to avoid social events, and so on. Please don’t skip it! It’s a great investment that makes your fast easier, smoother, and more efficient. Extended fasting isn’t just about motivation - it’s also about preparation and having a solid routine.

Hope this is useful, and happy fasting!