Extended Fasting: Benefits and Risks

The New Frontier of Fasting

Intermittent fasting has taken the wellness world by storm — but for some, eating within a 16:8 window no longer feels quite so groundbreaking. Enter extended fasting, also known as prolonged fasting: going without food for 24 hours or more in pursuit of sharper focus, deeper healing, and, in many cases, powerful weight loss.

It’s a bold move. For centuries, various cultures have used fasting for spiritual, mental, and physical clarity. But today’s extended fasting is often backed by science and fueled by the promise of detoxification, cellular repair, and even longevity.

Still, it’s not all smooth sailing. Going days without food comes with significant risks, especially if you don’t approach it with care.

This article explores what happens when you fast beyond 24 hours, including the evidence-based benefits, real-world drawbacks, and whether extended fasting could realistically (and safely) work for you.

What Counts as Extended Fasting?

Extended fasting refers to voluntarily abstaining from all caloric intake for more than 24 hours, typically 36, 48, or 72 hours. Some protocols stretch to 5 days or longer, though these are less common and often done under medical supervision.

During this time, only the following are typically allowed:

• Water (still or sparkling)
• Black coffee or plain tea
• Electrolytes or salt (non-caloric)
• Occasionally: diluted apple cider vinegar, herbal infusions

It’s different from intermittent fasting, which cycles between eating and fasting each day. Extended fasts are more like a temporary metabolic reboot.

The Potential Benefits of Extended Fasting

1. Autophagy: Your Body’s Cellular Cleanup Crew

Autophagy, derived from the Greek for “self-eating,” is the body’s way of clearing out damaged cells and recycling old components. It kicks in after 24–36 hours of fasting and may protect against age-related diseases.

Japanese scientist Yoshinori Ohsumi won a Nobel Prize in 2016 for his work on autophagy, highlighting its critical role in disease prevention and cell renewal.

Think of it as spring cleaning at the cellular level.

2. Deep Ketosis and Fat Adaptation

After roughly 24–48 hours without food, insulin levels plummet, and the body enters deep ketosis, burning fat for fuel. This can accelerate fat loss and train your metabolism to become more flexible.

While shorter fasts like the One Meal a Day (OMAD) protocol tap into fat stores, prolonged fasting pushes this adaptation further, especially for those with stubborn weight or insulin resistance.

3. Improved Insulin Sensitivity and Blood Sugar Control

Extended fasting gives the pancreas a rest, which can reduce insulin resistance and regulate blood sugar, particularly helpful for people with prediabetes or type 2 diabetes (with supervision).

In fact, several small studies have shown that multi-day fasting may even reverse insulin resistance markers temporarily.

If managing glucose is a top priority, intermittent fasting for people with diabetes may be a more moderate starting point.

4. Mental Clarity and Mood Stability

Many people report a boost in mental sharpness and emotional resilience after the first 36 hours of fasting. Once the hunger hormone ghrelin drops and ketones rise, the brain runs on a cleaner-burning fuel, potentially enhancing focus, memory, and even mood.

Anecdotally, extended fasting is said to support creativity, decision-making, and even spiritual insight, though this varies by individual.

What Happens in the Body During an Extended Fast?

The Risks and Side Effects of Extended Fasting

Despite its powerful appeal, extended fasting is not without pitfalls. The deeper the fast, the more crucial it becomes to monitor symptoms and know when to stop.

1. Electrolyte Imbalances

Without food, your body loses sodium, potassium, and magnesium through urine.

This can lead to symptoms like:

• Dizziness or light-headedness
• Muscle cramps
• Fatigue or weakness
• Irregular heartbeat

To prevent this, many seasoned fasters add electrolyte powders or salt water to their routine, especially beyond the 48-hour mark.

2. Nutritional Deficiency (Over Time)

One or two prolonged fasts won’t deplete your nutrient stores, but frequent extended fasting without proper refeeding can lead to vitamin and mineral deficiencies, particularly B vitamins, iron, and protein.

For this reason, it’s important to break your fast mindfully. If unsure, you might explore safe strategies in breaking your fast with nutrient-dense foods.

3. Slowed Metabolism (If Overdone)

Short fasts typically maintain or boost metabolism. However, frequent extended fasting, particularly without adequate refeeding, may lower metabolic rate over time—a protective adaptation against perceived starvation.

To avoid this, many experts recommend spacing prolonged fasts weeks apart and ensuring your non-fasting days include enough calories and protein.

4. Risk for Disordered Eating

While many people fast for health reasons, extended fasting can blur into restrictive or obsessive behaviours. It’s not suitable for anyone with a history of disordered eating, such as anorexia, bulimia, or orthorexia.

Watch for signs like guilt after eating, obsession with fasting length, or anxiety around food.

Who Should Avoid Extended Fasting?

Extended fasting isn’t recommended for:

• Children and teenagers (still growing)
• Pregnant or breastfeeding women
• Underweight individuals (BMI <18.5)
• Anyone with an eating disorders history
• People on medications that require food intake
• Type 1 diabetics or insulin-dependent individuals
• Those with adrenal or thyroid imbalances

Always consult a doctor or registered dietitian before attempting a fast lasting more than 24 hours, especially if you’re managing a health condition.

When Might Extended Fasting Be Worth Trying?

If you’re in generally good health and:

• Want to break a weight loss plateau
• Are you interested in mental clarity or a spiritual reset
• Are you managing mild inflammation or insulin resistance
• Feel comfortable with shorter fasts and want to level up

Then, a 36- to 48-hour fast, done occasionally, could offer a powerful reset—provided it’s approached safely and followed by replenishing meals.

How to Break an Extended Fast Safely

This can make or break your experience. After 48–72 hours of fasting, your gut is more sensitive, and rushing back into heavy meals can cause:

• Bloating
• Nausea
• Blood sugar spikes
• Digestive distress

Best foods to break a fast:

• Bone broth
• Lightly steamed vegetables
• Eggs
• Avocado
• Cooked lean meats
• Fermented foods (in small quantities)

Avoid alcohol, refined carbs, or high-fibre meals right away. Let your digestive system ease back into gear.

Real Experience: Leo’s 3-Day Fast

Leo, a 42-year-old graphic designer, tried a 72-hour fast after months of 16:8 and a few 24-hour fasts. He prepped by tapering down his meals and stocking up on electrolytes.

“The second day was the toughest — my head was foggy, and I was craving crisps like mad. But by day three, I was oddly calm and energised. I ended the fast with chicken broth and roasted veggies. Felt amazing the next day.”

He now does a 48-hour fast once a month and says it’s like “resetting his brain.”

How Often Can You Do Extended Fasting?

There’s no universal answer. Some people do it quarterly, others once a month. The key is listening to your body, tracking how you feel, and allowing full recovery between fasts.

Tips to keep in mind:

• Space fasts at least 3–4 weeks apart
• Avoid pairing with intense training or stress
• Prioritise sleep, hydration, and nourishment post-fast
• Stop immediately if you feel weak, faint, or unwell

Extended fasting is a tool, not a cure-all. Use it strategically, not obsessively.

Conclusion: Extended Fasting Isn’t for Everyone — But It Can Be Powerful

Extended fasting offers a compelling list of benefits: fat burning, improved insulin function, mental clarity, and even cellular renewal. But it also carries risks, particularly when it’s done too frequently or without preparation.

The key lies in balance and individualisation. Some thrive on the simplicity and metabolic shift of a 48-hour fast. Others find it too extreme and better suited to more moderate approaches like intermittent fasting or time-restricted eating.

If you’re curious about extended fasting, start with shorter fasts and gradually build up. Track how your body responds. Stay hydrated. Be honest with yourself.

And most importantly, break your fast with care and kindness.