I just completed a 72 hour fast for the purpose of gaining the health benefits attributed to fasting

[Squire]

Do I notice anything afterthe fast? Nothing discenible yet apart from a 3 kg weight loss.

There was no gout flare-up which is one of the identified risk factors.

No pain or discomfort either external or internal.

Time will tell.

Below is what Google AI said about fasting:

What is the longest fasting period for maximizing health benefits.

This is one of those topics where the benefits rise fast at first… then flatten out, while risks keep climbing. So “longest” is not the same as “best”.
Here’s the evidence-based sweet spot.
The fasting length that maximizes health benefits (for most people)
48–72 hours is the upper limit of benefit for most healthy adults
Beyond this, benefits plateau and health risks increase.
What happens at different fasting lengths
🟢 16–24 hours (Intermittent fasting)
Strong benefits, very safe

• Improved insulin sensitivity
• Lower inflammation
• Better metabolic flexibility
• Mild autophagy
• Cardiovascular benefits

This is the best long-term, repeatable strategy.
🟡 36–48 hours
Peak benefit zone

• Autophagy significantly increases
• Ketosis deepens
• Insulin drops sharply
• Growth hormone rises
• Immune system renewal begins

Many researchers consider 36–48h the maximum benefit / minimum risk point.
🟠 48–72 hours
Maximum autophagy & immune effects

• Autophagy near peak
• Old immune cells cleared
• Stem-cell-driven immune regeneration (shown in humans)
• Very low insulin

Risks start to appear:

• Electrolyte imbalance
• Muscle loss
• Dizziness, hypotension
• Gout flares (important if you’re on allopurinol)

Only for healthy adults, not frequently, and ideally supervised.
>72 hours
No extra health benefit for most people

• Autophagy does not increase much more
• Muscle breakdown accelerates
• Electrolytes become dangerous
• Heart rhythm risk increases

Extended fasts (>3–5 days) are medical interventions, not wellness tools.
So what’s the optimal answer?
Best overall:
16–24h regularly (daily or 3–5×/week)
Best “deep reset” (occasional):
36–48h, 1–3× per year
Not recommended for health optimization:
Anything over 72h without medical supervision
Who should NOT do long fasts (≥36h)

• Gout sufferers (uric acid spikes)
• Diabetes (especially on insulin)
• Kidney disease
• Underweight individuals
• Older adults without supervision
• Anyone on BP or heart meds

Often overlooked: re-feeding matters
The benefits of fasting are lost if you refeed badly.
Best post-fast:

• Protein first
• Vegetables
• Minerals (salt, potassium)
• Avoid sugar/alcohol for 24h

Bottom line
You don’t need extreme fasting to get extreme benefits.
For human health, longevity, and metabolic repair:

36–48 hours is the longest fast that maximizes benefit while minimizing risk.

If you want, I can tailor this to:

• Longevity vs weight loss
• Gout-safe fasting
• Older adults
• Women vs men
• Religious fasting (Ramadan-style)

 

[Squire]

The reported benfits of autophagy from fasting:

72-hour fast sits in the range where activation is thought to be strongest.


Documented Biological Benefits

Important: these are cellular or physiological benefits, not guaranteed disease cures.

1. Removal of Damaged Proteins

Cells accumulate defective proteins over time.

Autophagy:

• dismantles these proteins
• prevents toxic buildup

This process is strongly linked to healthy cellular aging.

2. Mitochondrial Quality Control (“Mitophagy”)

Damaged mitochondria produce excess oxidative stress.


Autophagy selectively removes weak mitochondria and promotes healthier replacements.

Result:

• improved cellular energy efficiency.

3. Reduced Inflammation

Autophagy helps regulate immune signaling by removing inflammatory triggers inside cells.

Observed effects:

• reduced inflammatory markers
• improved immune regulation.

This likely contributes to improvements in inflammatory conditions.


4. Metabolic Reset Effects

Autophagy helps cells adapt to fuel scarcity by:

• improving insulin sensitivity
• enhancing fat metabolism
• stabilizing energy use

5. Cellular Survival During Stress

Autophagy provides emergency fuel from internal recycling.

Evolutionarily, this allowed humans to survive food scarcity without destroying essential tissues immediately.


Why Autophagy Exists (Evolutionary View)

Humans evolved with irregular food availability.

Fasting signaled:

“Resources scarce → repair and optimize instead of grow.”

So the body:

• pauses growth
• fixes damage
• conserves energy.

Modern constant eating keeps many people in near-continuous growth signaling.


Common Misconceptions
“Autophagy detoxifies the body”

Not exactly.


Your liver and kidneys detoxify chemicals.
Autophagy recycles internal cell components, not environmental toxins.


“More fasting = more autophagy indefinitely”

False.

After prolonged fasting:

• metabolism slows
• protein loss increases
• benefits plateau.

There is likely an optimal window rather than unlimited gain.

“Autophagy only happens during fasting”

Incorrect.

It occurs constantly at low levels:

• exercise
• sleep
• calorie restriction
  also increase it.

Strength of Scientific Evidence

Evidence area	Strength
Cellular biology	Very strong
Animal lifespan studies	Strong
Human metabolic markers	Moderate-strong
Human longevity proof	Not yet proven

Human studies confirm activation pathways but long-term outcomes are still being researched.


Why People Sometimes Feel Better After 2–3 Days Fasting

Likely combination of:

• ketosis (stable brain fuel)
• reduced inflammation
• hormonal changes
• autophagy-related cellular cleanup

Autophagy itself is microscopic — you don’t directly “feel” it — but its downstream effects may be noticeable.

A subtle but important insight

Autophagy is not primarily about weight loss.

It is about:
cellular maintenance during energy scarcity.
Weight loss is secondary.

 

[Squire]

I did this fast because I wanted to experience the mitochondria rebuild and upgrade to observe what benefits there wer form this.

I already appear to have experienced one benefit from the fast. I have nocturia, and waking up at around 3:15 am is common. This morning I awoke at 3:15 am as usual but did not feel a need to empty my bladder and continued to sleep until 5:40 am.

I will see if this continues.

Here are the mitochondrial benefits:

Many researchers now believe that a large share of fasting’s real biological benefit happens after the fast, during the refeeding phase, when mitochondria rebuild and upgrade themselves.


Here’s what is happening biologically.


Why the Post-Fast Period Is So Important

During a 72-hour fast your body mainly does:

• cleanup (autophagy)
• removal of damaged mitochondria (mitophagy)
• metabolic reset

But it does not fully rebuild yet — because rebuilding requires nutrients.


When you start eating again, the body receives a powerful signal:

“Resources available — rebuild using the improved blueprint.”

This triggers a unique anabolic–repair state.


Phase 1: The Fast (Demolition & Cleanup)

During fasting:


damaged mitochondria removed
inefficient cellular components recycled
inflammation reduced
insulin sensitivity restored


But:

• protein synthesis is suppressed
• growth pathways are low.

You are preparing the ground — not constructing yet.


Phase 2: Refeeding (Reconstruction Phase)

Once food returns:

1. Mitochondrial Biogenesis Accelerates

Key pathways activate:

• mTOR (controlled growth signal)
• PGC-1α (mitochondrial master regulator)
• AMPK rebound signaling

Cells begin producing new mitochondria.


These new mitochondria tend to be:

• more efficient
• less damaged
• better adapted to fat metabolism.

This is sometimes called metabolic renewal.


2. Nutrient Partitioning Improves

After fasting, muscles and organs become highly nutrient-sensitive.


Incoming nutrients preferentially go toward:

• repair
• glycogen restoration
• mitochondrial rebuilding

rather than fat storage (if overeating is avoided).


This is why moderate refeeding often produces a feeling of strong vitality.


3. Stem Cell Activation (Evidence Emerging)

Animal studies and limited human data suggest fasting followed by feeding can stimulate regeneration signals, especially in:

• immune cells
• intestinal lining
• blood cell precursors.

The fast creates demand; feeding supplies building material.


4. Improved Insulin Signaling Window

For several days after fasting:

• insulin sensitivity is elevated.

Meaning:

• lower insulin needed
• glucose handled efficiently
• reduced metabolic stress.

This window can last roughly 3–7 days.


Why Exercise After a Fast Multiplies Benefits

Light-to-moderate exercise during refeeding strongly amplifies mitochondrial renewal.


Exercise signals:

“We need more energy capacity.”

Cells respond by building more mitochondria.


This combination (fast → eat → move) mimics ancestral feast-and-hunt cycles.


What People Often Feel During This Phase

Common reports (when done correctly):

• unusually stable energy
• improved mental clarity
• reduced inflammation symptoms
• better digestion
• improved sleep

These correlate with improved mitochondrial function.


The Critical Mistake: Poor Refeeding

Many benefits disappear if refeeding involves:

• very large meals immediately
• high sugar intake
• alcohol
• ultra-processed foods
• low hydration

This causes:

• insulin spike
• oxidative stress
• digestive overload

and can negate mitochondrial gains.


Ideal Refeeding Strategy (Physiology-Based)
First 24 hours

• smaller meals
• easy digestion
• moderate protein
• some fiber
• good hydration + electrolytes

Examples:

• vegetables
• yogurt or eggs
• fish
• soup/broth
• fruit in moderation

Days 2–5

Add gradually:

• complex carbohydrates
• healthy fats
• normal protein intake

Include walking or light resistance exercise.


Avoid initially

• heavy fried foods
• alcohol
• large red-meat meals
• binge eating.

Simple Summary

Phase	Mitochondrial Role
Fasting	Remove damaged units
Early refeeding	Build new mitochondria
Movement	Strengthen energy capacity
Stable diet	Maintain improvements

The Big Insight (What most discussions miss)

Fasting is not the benefit by itself.


It works as a biological reset switch:

Stress → Cleanup → Nutrients → Rebuild Better

Without the rebuild phase, you only get half the effect.

 

[HBS Guy]

Must have gotten hungry! You did drink water I assume.

 

[johnsmith]

Evidence behind intermittent fasting for weight loss fails to match hype | Cochrane

 

[greggerypeccary]

Evidence behind intermittent fasting for weight loss fails to match hype | Cochrane

Yeah, I heard them talking about that on the radio yesterday.

Seems there's no evidence to support the case for weight loss.

 

[Squire]

Yeah, I heard them talking about that on the radio yesterday.

Seems there's no evidence to support the case for weight loss.

I didn't do it for weight loss. I did it for the perceived benfits of mitochondrial action for cell repair and cell renewal.

There was weight loss of ~1 kg per day but whatever your dietary habits were before the fast will put that weight back on.

Three days after the fast I only returned 1 kg of the three I lost during the fast with the same dietary regime I had before the fast.

I believe there were wellbeing benefits from the fast. I feel good.

 

[HBS Guy]

You might just feel good from completing the fast, achieving a goal.

 

[Squire]

You might just feel good from completing the fast, achieving a goal.

It is more than that.

Cells begin producing new mitochondria.

These new mitochondria tend to be:

• more efficient
• less damaged
• better adapted to fat metabolism.

This is sometimes called metabolic renewal.