5 Day Fast Weight Loss: How Many Pounds Can You Lose?

Fasting comes in different forms for various purposes. 

Religious fasting, for example, is often done for spiritual reasons. 

Medical fasting, on the other hand, is prescribed for therapeutic reasons (1).

Intermittent fasting has become popular in health and fitness due to its potential weight-loss benefits (2). One of the most extreme forms of fasting is the 5 day fast.

Many wonder, “How long should you fast for weight loss?”

An extended fast (anything longer than 24 hours) can intimidate most people. 

After all, going without food for several days goes against our instinct to eat when we’re hungry. However, the potential weight loss benefits of a 5 day fast have made it a popular choice among those looking to shed pounds quickly.

We review the science behind 5 day fast weight loss and answer the following questions: 

• How many pounds can you lose in a 5 day fast? 
• Is a 5 day fast an effective weight loss method? 
• What are the potential risks and benefits?

What Is A 5 Day Fast?

A 5 day fast is where you don’t eat any food for 5 days straight and only drink water or zero-calorie drinks. Because it requires you to stop eating food for 5 days, most diet experts consider it an extreme form of intermittent fasting.

During this time, the body enters a state of ketosis, where it begins to burn stored fat instead of glucose for energy. 

When the body burns stored fat instead of glucose for energy, it can cause rapid weight loss. 

Research suggests that periodic fasting has potential therapeutic benefits, such as improved insulin sensitivity and reduced inflammation (3).

Health professionals have debated the safety of extended, water-only fasting. 

While some studies have shown potential benefits, there are also serious risks, especially for those with underlying medical conditions (4, 5).

A more important consideration is the sustainability of this type of fasting. Many people find it challenging to maintain such a restrictive eating pattern for 5 days, and sustainability is crucial for long-term weight loss success.

Does 5 Day Fast Help Lose Weight?

Short-term weight loss is a typical result of the 5 day fast. 

So what is a 5 day fast weight loss like?

One review found that fasting for 5-20 days resulted in weight loss of 2-10% of starting weight (5).

However, the amount of weight lost can vary significantly from person to person, depending on factors such as starting weight and body composition.

During an extended fast, the body uses stored glycogen (carbohydrates) for energy before switching to fat-burning (3). This initial depletion of glycogen stores leads to a significant drop in water weight, which can contribute to the initial weight loss seen on the scale.

After fasting depletes the glycogen stores, the body turns to fat for energy. 

This process is known as lipolysis and theoretically leads to more sustained weight loss during the fast (6).

Once you resume regular eating habits, you will likely regain all of this weight. Your body will replenish glycogen stores and restore water weight.

Many individuals tend to overeat and even binge after an extended fast, leading to rapid weight regain. This restriction leads to overeating after a 5-day fast if you haven’t built a solid foundation of healthy eating habits.

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How Bad Is Fasting For 5 Days?

Fasting for 5 days can place significant stress on the body and may carry several risks, mainly if not approached with caution or medical guidance. 

While some short-term benefits of fasting are possible, weighing them against the potential adverse effects is crucial.

Here’s a detailed look at the risks, challenges, and issues related to a 5 day fast, which will answer the popular question, “Is fasting for 5 days healthy?”

1. Nutrient Deficiencies

When you go without food for extended periods, your body lacks the vitamins, minerals, and macronutrients it needs to function correctly. 

A 5 day fast can involve the absence of essential nutrients, such as:

• Potassium
• B vitamins
• Magnesium

These vitamin deficiencies lead to symptoms such as:

• Fatigue
• Weakness
• Impaired focus
• Possible life-threatening health conditions (7). 

For example, electrolyte imbalances from insufficient potassium or magnesium can disrupt organ function and heart rhythms (8).

2. Dehydration

While fasting might suggest only abstaining from food, many people unknowingly drink insufficient water.

Not drinking enough water during a fast can lead to severe dehydration. 

Symptoms may include:

• Dizziness
• Dry mouth
• Headaches
• Low blood pressure
• Kidney strain over time (9). 

Since fruits, vegetables, and other foods contribute to our daily hydration, eliminating them for 5 days amplifies the risk of dehydration.

Read more: Will Coconut Water Break a Fast?

3. Muscle Loss

When fasting, your body exhausts its immediate energy stores (glycogen) within the first 1–2 days. 

After this, it begins breaking down fat for energy. 

However, the body may also start breaking down muscle tissue to obtain amino acids, which it converts into glucose for essential bodily functions like brain fueling (7). 

Prolonged muscle loss can reduce strength and negatively affect metabolism (10), especially if you repeat fasting without proper recovery.

4. Electrolyte Imbalance

Electrolytes, such as:

• Sodium
• Calcium
• Potassium
• Magnesium

All play a vital role in maintaining fluid balance, nerve function, and heart health. 

A 5 day fast significantly increases the likelihood of electrolyte imbalances, especially if you aren’t drinking additional fluids with electrolytes. 

Severe electrolyte imbalances can cause symptoms like:

• Fatigue
• Confusion
• Muscle cramps
• Irregular heartbeats
• In extreme cases, cardiac arrest (8).

5. Impact On Pre-Existing Health Conditions

A 5 day fast can be particularly harmful for individuals with certain medical conditions. 

Here are some examples:

• Diabetes: Fasting can cause dangerous drops in blood sugar (hypoglycemia) or spikes (hyperglycemia) when you resume eating, depending on how the body responds to the absence of food and insulin levels (11).
• Heart Conditions: Electrolyte imbalances and dehydration can strain the cardiovascular system, increasing the risk of heart issues (12, 13).
• Kidney Problems: Lack of hydration and strain on the kidneys during fasting can exacerbate pre-existing kidney issues (14).
• Eating Disorders: Fasting may trigger or worsen unhealthy relationships with food, particularly in people prone to disordered eating behaviors (15).

6. Risk Of Refeeding Syndrome

After fasting for 5 days, you must carefully handle reintroducing food. Refeeding syndrome occurs when you eat too quickly after prolonged fasting or malnourishment, and it’s dangerous (16).

The sudden influx of nutrients can cause severe shifts in electrolytes, particularly potassium, phosphorus, and magnesium, leading to complications such as:

• Seizures
• Heart failure
• Respiratory distress
• Even death (16).

You can avoid this by gradually refeeding, ideally under medical supervision, focusing on easily digestible foods in small portions and electrolyte replenishment.

The Importance of Medical Supervision

Without consulting a healthcare professional, you should never attempt extended fasting, such as a 5 day fast.

A healthcare provider can assess whether fasting is safe for you by considering the following:

• Medical history
• Nutritional needs
• Current health status

Medical supervision also allows monitoring of vital signs, electrolyte levels, and hydration to catch potential problems early.

A Balanced View

It’s worth noting that some people fast for health benefits, such as:

• Enhancing autophagy (the body’s cellular repair process) (17)
• Promoting short-term weight loss (18)
• Increased focus
• Mental clarity

However, these potential benefits must be carefully weighed against the risks, especially since not everyone experiences fasting the same way. 

The benefits of fasting don’t negate the possibility of nutrient depletion, muscle loss, or other serious complications, particularly for those with underlying health concerns.

What Happens When You Don’t Eat For 5 Days?

Not eating for 5 days triggers physiological and psychological changes in the body as it adapts to the lack of food. 

The body undergoes 3 main phases during a fast:

1. Glycogen depletion
2. Ketosis
3. Muscle breakdown (6, 19)

Stage 1: Glycogen Depletion (First 1-2 Days)

When you stop eating, your body initially relies on glycogen stored in the liver and muscles for energy. 

It breaks glycogen down into glucose, the primary fuel for cells.

Glycogen stores are limited and typically last 24-48 hours.

Once depleted, the body faces an energy deficit and must turn to alternative fuel sources. During this phase, you may experience:

• Blood sugar levels dropping
• Lightheadedness
• Headaches
• Dizziness
• Fatigue

Hormonal changes in insulin and cortisol levels can cause you to feel irritable or “hungry.”

Stage 2: Ketosis (Days 2-5)

After the body has depleted its glycogen stores, it begins breaking down fat reserves into molecules called ketones.

These ketones become the primary energy source for most cells. Your brain can use these ketones in the absence of glucose.

This metabolic state, ketosis, is your body’s way of adapting to prolonged fasting or starvation (20).

Challenges during ketosis include (20):

• Halitosis (bad breath) due to ketone production.
• Dehydration occurs when water output increases through urine when the body has no glycogen.
• Strain on the kidneys as they filter more urea, a byproduct of protein metabolism.
• Cravings and hunger pangs may persist, though they often lessen by the 5th day.

Despite the challenges, there are some benefits people seek through fasting:

• Energy: Some people report bursts of energy or clarity as ketone production stabilizes and replaces glucose as brain fuel (21).
• Weight Loss: This phase typically results in significant water weight loss as glycogen stores are burnt out and excreted.
• Autophagy: After 72 hours, the body may upregulate autophagy, a cellular cleanup process where old or damaged cells are broken down and recycled. Researchers have linked this process to reduced oxidative stress (17).
• Short-Term Weight Loss: 5 days of fasting can lead to weight loss, usually a combination of water weight, muscle mass, and fat.
• Mental Focus: During ketosis, some people report improved mental clarity (22), although results vary.

Stage 3: Muscle Breakdown And Starvation Mode (Day 4 And Beyond)

While the body prioritizes burning fat, it also begins breaking down muscle tissue to access amino acids. 

These amino acids help produce glucose through gluconeogenesis, which the brain and red blood cells still require for survival (23).

Prolonged muscle loss can:

• Weaken the body 
• Slow metabolism
• Lead to fatigue
• Physical decline (10). 

Muscle loss is especially concerning for individuals with lower body fat, as they may lose muscle more quickly.

However, the extent and rate of muscle breakdown can vary based on several factors, including:

• Body Composition: Individuals with higher body fat percentages may experience slower muscle breakdown as their bodies have more fat reserves for energy use.
• Activity Level: Physical activity during fasting can increase muscle breakdown as the body requires more energy. The type and intensity of activity play significant roles in determining the extent of muscle preservation or loss.
• Protein Intake: Consuming some protein during fasting (e.g., in modified fasting diets) may help preserve muscle mass (10).
• Metabolic Rate: A higher metabolic rate can lead to faster depletion of energy stores, potentially accelerating muscle breakdown.

Explore a detailed Timeline Of Fasting and learn how experts have linked each fasting stage to different benefits.

System Slowdown

When the body goes into “starvation mode” to conserve energy, its metabolic rate decreases, which can lead to weight regain later. Non-essential bodily functions, like temperature regulation or reproductive processes, may also slow down (24).

Potential Electrolyte Imbalance

Prolonged fasting can lead to a dangerous loss of electrolytes, such as sodium, potassium, and magnesium (7).

The Importance Of Hydration And Electrolytes

Maintaining proper hydration and electrolyte balance is critical during any extended fast. 

Drinking water isn’t enough—you also need electrolytes like sodium, potassium, and magnesium to keep muscles, nerves, and the heart functioning (25). 

Supplements such as electrolyte powders or broths may help, but fasting 5 days without professional guidance still carries significant risks.

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How To Do A 5 Day Fast Safely?

Fasting for 5 days can be a physical and mental challenge, but you can practice safety by taking a thoughtful approach that involves proper preparation and care. 

Follow this step-by-step guide to understand the 5 day fasting stages and ensure a safer and more manageable fasting experience.

Step 1. Preparation Before the Fast

Preparation is crucial before a 5 day fast to help your body transition and reduce potential side effects.

Gradual Reduction In Food Intake 3-5 Days Before:

• Gradually reduce portion sizes.
• Focus on lighter meals, such as salads, soups, and steamed vegetables.

Eliminate Stimulants:

• Reduce caffeine and alcohol intake to avoid withdrawal symptoms during the fast.

Eat Only Nutrient-Dense Foods

• In the days before the fast, eat fruits, vegetables, whole grains, and lean proteins to ensure your body has adequate stores of essential nutrients.
• Consider taking a multivitamin (with your doctor’s approval) a few days before fasting.

Plan For Rest:

• Choose a period when you can rest as needed. Avoid fasting during periods of strenuous work, travel, or intense activities.
• Inform those around you, such as family or coworkers, so that they can respect your need for lower energy commitments.

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Step 2: During The Fast

Once you’ve begun the fast, your focus should be hydration, electrolyte balance, and monitoring your feelings.

Prioritize Hydration:

• Drink plenty of water throughout the day. Aim for at least 2-3 liters daily to prevent dehydration.
• Include herbal teas or broths (without solid ingredients) to keep your stomach settled.

Maintain Electrolyte Balance:

Consider supplementing with sodium, potassium, and magnesium to replenish lost electrolytes. You can:

• Drink salt water mixtures (e.g., ¼ tsp Himalayan salt dissolved in water).
• Use no-calorie electrolyte supplements or powders.
• Sip homemade broths without any solid ingredients.

Monitor Your Activity Level:

• Stick to low-intensity activities, such as walking, stretching, or yoga.
• Over-exertion can increase fatigue and muscle breakdown.
• High-intensity activities can deplete energy and electrolytes rapidly, increasing risks of dizziness, fainting, or injury.

Listen To Your Body:

Watch for warning signs that indicate it might be time to stop fasting, such as:

• Heart palpitations
• Severe dizziness or fainting
• Persistent nausea or vomiting
• Confusion or inability to focus

If symptoms feel unusual or dangerous, stop the fast and seek medical attention if necessary.

Our previous publication features a sample 5 Day Fasting Diet Meal Plan.

Step 3: Breaking the Fast Safely

The refeeding phase is just as critical as the fasting period itself. 

Your digestive system becomes more sensitive after prolonged fasting, so you must reintroduce food gradually.

Start eating at a slow pace.

First 6-12 Hours:

Begin with small portions of easily digestible foods, such as:

• Steamed vegetables
• Diluted fruit juices
• Plain yogurt
• Bone broth

Avoid heavy, fatty, spicy, and high-carbohydrate meals immediately after fasting. These can overwhelm your system and lead to discomfort (16).

24-48 Hours Post-Fast:

Gradually reintroduce solid foods in small amounts, focusing on whole, nutrient-dense options like:

• Cooked vegetables
• Lean proteins
• Healthy fats

Avoid overeating; your body will need time to readjust to regular food intake.

Step 4 – Lower Refeeding Syndrome Risks

Refeeding syndrome occurs when a rapid influx of food after fasting causes dangerous shifts in electrolytes (16). 

To minimize risks:

• Continue taking electrolytes during the re-feeding phase.
• Avoid consuming high-calorie or carbohydrate-dense meals immediately after fasting.

Consult a Healthcare Professional

Before attempting a 5 day fast, it’s crucial to seek advice from your doctor, especially if you have any of the following concerns (27):

• Pre-existing medical conditions, such as diabetes, GERD, or kidney problems
• Need for medications that require food for absorption
• History of disordered eating

Medical guidance ensures you understand potential risks and can tweak your fasting approach for safety.

Learn more about safety when it comes to fasting in our previous post – How Long Is It Safe To Fast?

Read more: Fasting While Working Out: Best Strategies for Maximum Results

What Is Allowed On A 5 Day Fast?

To stay hydrated and maintain essential body balances during your 5 day fast, primarily consume:

• Water
• Clear broths (vegetable, bone, or chicken)
• Unsweetened black coffee and herbal teas
• No-calorie electrolyte supplements or powders

Ensure they are free of solid ingredients and made without added sugars or oils. Avoid solid foods and caloric beverages unless you follow a modified fasting plan. 

Frequently Asked Questions

• Can you lose weight from intermittent fasting for 5 days?

Yes, you can lose weight intermittent fasting for 5 days. The weight loss happens because fasting reduces calorie intake, which can lead to weight loss (18). 

However, most of the weight lost is water weight, which will return when you resume eating and replenish your glycogen stores.

• Can I drink water while fasting?

Yes, you can and should drink water while fasting. Staying hydrated is vital for supporting your body and preventing dehydration (28).

• Can I drink Coke Zero while fasting?

You can drink Coke Zero while fasting since it contains zero calories. However, consuming artificial sweeteners may trigger hunger in some individuals, so it’s best to monitor how your body responds.

• Can I eat eggs after a 5 day fast?

You can eat eggs after a 5 day fast, but reintroduce them gradually. Start with small portions of easy-to-digest foods like boiled or poached eggs to avoid overwhelming your digestive system.

The Bottom Line

When you don’t eat for 5 days, your body undergoes three main phases: glycogen depletion, ketosis, and muscle breakdown. 

While short-term fasting might offer benefits like: 

• Weight loss
• Autophagy
• Temporary mental clarity

A 5 day fast also comes with risks such as:

• Irritability
• Muscle loss
• Dehydration
• Electrolyte imbalance
• Cognitive impairments
• Obsessive thoughts about food

If you’re considering fasting for an extended period, consult a healthcare professional. Medical supervision is crucial for managing risks and ensuring your safety.