Momentum in the Mountains 2024


The Different Stages of Fasting

author avatar Dr. Eric Berg 06/11/2024

Fasting can offer a myriad of health benefits, but it can also be a difficult journey. Understanding fasting will help you have a smooth start, rather than struggling through the process and being tempted to quit.

Learn about fasting, its different stages, and what you can do to ensure a successful fast.

Understanding the First Stage of Fasting

Think of your body like a hybrid car that can switch fuel sources. During the first stage of fasting, usually 8 to 14 hours after your last meal, it's like flipping a switch from using glucose as its primary energy source to tapping into glycogen reserves.

This is where blood sugar levels start to stabilize.

The Shift from Glucose to Glycogen

In this early phase, our bodies begin a balancing act. Your muscles begin burning half glucose and half fat right around the 10-hour mark—this marks an important transition towards fat-burning mode.

Your body isn't just burning through leftovers; it's gearing up for more efficient fuel use down the road.

To put things into perspective, scientific studies have shown that during these initial hours without food, our insulin levels decrease, prompting cells throughout our body to break down glycogen—the stored form of sugar—and release it as glucose for energy.

The Ketosis Kickstart

Imagine your body is a hybrid car, smoothly switching from gasoline to electric power. That happens when you fast, and your liver turns fat into ketones—a cleaner, more efficient fuel for your brain and muscles.

Within 14 to 24 hours of fasting, you're starting to have decreased cravings and increased energy.

Benefits of Ketone Production

Ketones are like supercharged battery packs that help boost mood and sharpen focus. They don't just change our feelings; they rewire our internal workings for better performance.

As these little molecules proliferate, they send anxiety packing and bring cognitive function front and center.

Beyond feeling great mentally, this metabolic switch flips other switches, too. So, let go of sugar highs in favor of sustained ketone-powered vitality.

Human brain illustration

Achieving Full Ketosis and Brain Health

When you hit the 24-hour mark of fasting, your body is not just burning fat—it's entering full ketosis. Think of your liver as an exclusive bouncer, turning away carbs and welcoming in those fats to convert into energy-rich ketones.

This metabolic switch-up doesn't just shrink your waistline; it also reduces the hunger alarms by reducing ghrelin levels.

The production of BDNF ramps up like a factory on overtime during this third stage, lasting until around 36 hours. What does that mean for you? Imagine BDNF as fertilizer for your gray matter; it helps sprout new neural connections.

So, while waving goodbye to pesky cravings, say hello to improved memory and learning capabilities—a real brainpower boost.

Autophagy and Cellular Housekeeping

Think of autophagy as a super-efficient recycling program inside your body. When you hit that 36 to 48-hour mark in fasting, it's go-time for cellular cleanup duty.

Your cells get busy breaking down all the junk they've accumulated - think damaged proteins and pesky microbes.

The Process of Autophagy

Through autophagy, cells dismantle the old bits and pieces, then repurpose them to build fresh components or generate energy.

It’s an intricate process of breakdown and renewal within our tissues.

Beyond keeping things tidy at a microscopic level, this process is critical in dodging diseases by clearing out potential troublemakers before they can cause harm.

Health Benefits of Enhanced Autophagy

The perks don’t stop there. This cell-level housekeeping slashes oxidative stress from environmental no-nos like pollution while cutting down misfolded proteins linked to chronic illnesses such as Alzheimer’s.

You're not just cleaning up—you’re renovating for resilience against aging and inflammation.

Extended Fasting and Muscle Preservation

If fasting for two days or more will send your muscles packing, think again. Once you cross the 48-hour mark of a fast, your body starts to get pretty savvy about what it burns for energy.

Instead of using muscle, it goes into preservation mode.

During this fifth stage of fasting, around 48 to 60 hours without food, the magic happens. Your insulin sensitivity sharpens; inflammation reduces, and muscles start healing from any atrophy they've suffered in the past. It's all thanks to protein sparing—a fancy term for when your body decides to protect its muscles by focusing on autophagy instead.

This cellular cleanup crew turns damaged proteins into new ones so you can heal while still rocking that lean look. You see, rather than letting valuable muscle go to waste, your body recycles itself like an eco-friendly superhero.

Immune System Renewal Through Fasting

Fasting for 60 to 72 hours flips a regenerative switch in your immune system. Think of it as hitting the refresh button; during this final fasting stage, your body experiences a surge in immune stem cell production.

A 2014 study demonstrated that extended periods without food could significantly reboot the immune system. By depleting white blood cells, fasting triggers regeneration, leading to new cells and renewed defense mechanisms.

This period is when your body performs deep maintenance work on its cellular security team—imagine upgrading from mall cops to special forces—and emerges stronger against infection and disease.

Woman preparing celery juice

Unlocking Health Gains and Detoxifying Benefits

Embark on a transformative journey through the six stages of fasting, unlocking a spectrum of health gains and detoxifying benefits.

This subtopic illuminates the nuanced relationship between fasting and detox, emphasizing how each stage contributes to the body's natural cleansing process.

Navigating these stages offers individuals a holistic approach to fasting to detox, providing rejuvenation and health enhancements and a profound understanding of the synergistic effects of fasting on overall well-being.


Fasting offers numerous health benefits, but understanding the process is key. Remember to consult a medical professionalbefore embarking on a fast of any length.

As fasting continues, ketone production begins, enhancing energy and mental clarity. Around 24 hours, full ketosis boosts brain health and reduces hunger. At 36 to 48 hours, autophagy cleans out cellular debris, reducing disease risk.

Extended fasting beyond 48 hours preserves muscle and reduces inflammation, while fasting for 60 to 72 hours regenerates the immune system.

Fasting isn't just about skipping meals—it's about harnessing the body's natural ability to heal and thrive, providing detoxifying and rejuvenating benefits.

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