24 Vs. 36-Hour Fast: What’s the Difference?

Extended fasting has garnered considerable attention due to its numerous health benefits. Many people find it a handy tool to support weight loss, improve metabolic function, and promote cellular repair.

When it comes to fasting, there are numerous options, making it challenging to determine which one is right for you. 

Two popular fasting durations that often spark interest are the 24-hour and 36-hour fasts. While both have significant health benefits, choosing between them will depend on your experience level, goals, medical history, and lifestyle. 

Understanding the pros and cons of these fasting methods can help you make an informed decision about which approach aligns most with your health goals. 

Here, we will take a closer look at the science behind each fasting duration, its benefits, potential risks, and practical tips for doing it safely. However, if you are new to fasting, remember that it’s always best to consult a healthcare professional to determine if fasting is suitable for you. 

Every fast is a personal experience. Your dietary preferences, body composition, and activity level all influence your fasting journey. It’s advisable to consult with a healthcare provider before embarking on a fasting regimen.

What Is Fasting? 

Fasting is the voluntary abstention from food for a specific period, while maintaining proper hydration. Unlike starvation, fasting is a controlled practice that allows your body to enter a distinct metabolic state, promoting healing and cellular repair. 

During fasting periods, your body shifts from using glucose as its primary energy source to burning stored fat for energy. This metabolic switch typically happens around 12-16 hours into a fast, marking the beginning of ketosis (a state where your liver produces ketones from a fat breakdown).

When it comes to fasts lasting longer than 24 hours, it allows your body to adapt to these metabolic changes, potentially offering greater benefits than shorter intermittent fasting windows. That is why the duration you choose can significantly impact the depth of these metabolic shifts and benefits.

What Are The Benefits Of Fasting? 

There are several benefits to 24-hour fasts and 36-hour fasts. 

Here are some of the benefits you may experience when you include extended fasts: 

• Better Blood Glucose Levels: Fasting may help improve insulin sensitivity, allowing your cells to respond more effectively to insulin, which results in better blood glucose levels (2). 
• Enhanced Weight Loss: Another benefit of fasting is that it may promote fat oxidation, encouraging the body to burn stored fat for energy rather than relying only on dietary glucose (4). Additionally, a shorter eating window can indirectly lead to a caloric deficit (eating fewer calories than the body needs) to promote weight loss.
• Cellular Repair and Longevity: One of the most significant benefits of extended fasting is the activation of autophagy (your body’s cellular cleaning process) (1). During autophagy, cells break down and recycle damaged components, which can potentially reduce inflammation and promote longevity. 
• Improved Cognitive Health: Some people report improved mental clarity and focus during extended fasts (3). This improved cognitive function may be the result of increased ketone production, which is an efficient fuel source for the brain.

What Is The Difference Between A 24-Hour And A 36-Hour Fast?

Many wonder, “What is the difference in benefits of 24 vs 36-hour fasts?”

The main difference between these two fasting durations lies in the depth and duration of the metabolic changes the body can experience. In both fasts, you can experience the benefits of ketosis, but in a 36-hour fast, you may experience more profound metabolic changes. 

The additional 12 hours provide more time for autophagy to happen and allow your body to fully adapt to using ketones as fuel. This extended period in a 36-hour fast may offer enhanced fat burning and more significant cellular repair benefits.

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Is It Safe To Jump From 24 To 36 Hour Fasts? 

Going from a 24-hour to a 36-hour fast requires careful consideration and a gradual progression. While many people can safely make this transition, jumping too quickly may lead to uncomfortable side effects and potential health risks. 

First, establish a consistent 24-hour fasting routine before attempting longer durations. Once you master the 24-hour fast by doing it for several weeks (or even months), you can start thinking about transitioning to a 36-hour fast. 

When you are ready to do the transition, start by increasing your fasting by 2-4 hours until you reach the 36-hour mark. 

This progressive approach can help minimize 36-hour fasting side effects and allow your body time to adjust naturally to 36-hours fasting benefits.

Warning Signs To Watch For

Pay attention to your body’s signals during the transition. If you experience severe fatigue, dizziness, nausea, or difficulty concentrating, it may be that you are progressing too quickly or that longer fasts aren’t suitable for you. 

And, if you have any underlying conditions like diabetes, eating disorders, or heart conditions, make sure you consult with a healthcare provider before attempting extended fasts. Additionally, pregnant or breastfeeding women should avoid fasting altogether. 

What Happens In The Body Between 24 And 36 Hours? 

Autophagy begins during the first 24 hours of fasting, but the process can intensify significantly between hours 24 and 36. This extended cellular cleanup period enables a more thorough removal of damaged proteins and cellular debris. 

Additionally, ketone production continues to increase throughout the fasting period, potentially reaching higher levels during a 36-hour fast compared to a 24-hour fast. Higher ketone levels may result in greater weight loss benefits and possibly improved cognitive functions. 

The extended fasting period may also help trigger additional hormonal adaptations, including increases in growth hormone and norepinephrine (5). For some individuals, this may result in better muscle preservation and enhanced fat loss. 

Read more: First Meal After Fasting: What To Eat, What To Avoid, And How To Reintroduce Food The Right Way

Are There Major Energy Dips Past 24 Hours Of Fasting? 

Many people experience different energy patterns during extended fasts. 

During a 24-hour fast, some individuals may experience increased fatigue or mental fog. 

This temporary energy dip occurs as your body continues to adapt to ketone metabolism and may feel more pronounced than earlier fasting periods. 

However, this energy dip is typically temporary and often followed by improved energy and mental clarity as ketone production stabilizes. 

Between hours 24 and 36, energy levels often stabilize or even improve as your body becomes more efficient at using ketones for fuel. Many people report feeling surprisingly energetic and mentally sharp. 

Remember that the key to managing energy during this extended period is maintaining proper hydration and electrolyte balance. 

Which Is More Effective For Fat Loss: 24 Vs 36-Hour Fast?

Both 24-hour and 36-hour fasts can be effective for weight loss, but they may suit different people and lifestyles.

The benefits of 24-hour fasting and a 24 hour fast vs 36 hour fast involve creating a significant caloric deficit while still being manageable for most people. 

Regular 24-hour fasts can lead to sustainable weight loss if combined with healthy eating patterns during non-fasting days. 

How much weight can you lose in a 24-hour fast? It depends on the individual.

However, in most cases, people can lose between 1 and 3 pounds per week. But keep in mind that in some cases, the majority of “weight loss” is water loss. 

As we’ve seen, 36-hour fast weight loss can occur because the extended fasting period may result in potentially bigger fat burning and higher ketosis levels. 

These increased levels enable more complete glycogen depletion and better utilization of fat stores as an energy source. 

However, the benefits of fasting and weight loss depend on:

1. Individual metabolic functions.
2. The food consumed during non-fasting days.

If you are struggling to do an extended fast, you may benefit more from a 24-hour fast. 

However, if you find yourself having more energy after the 24-hour mark, a 36-hour fast may be more beneficial for you. Ultimately, it will depend on your lifestyle, stress levels, and ability to practice fasting consistently. 

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Which Fast Is Better For Beginners? 

For most beginners, neither option is a good choice. 

A 24-hour fast may be too challenging to start with. In this case, it’s best to start with a 14 or 16-hour fast. As you start increasing your fasting hours, set a goal to reach a 24-hour fast. 

Beginning slowly can help you:

• Maintain hydration
• Manage your hunger
• Recognize your body’s signals. 

This gradual pace can help you eventually increase your fasting hours without putting too much strain on your body. 

How Should You Break A 36-Hour Fast?

Breaking a fast is just as important as the actual fast. 

After an extended fasting period, your digestive system needs time to readjust to processing foods. Start with small portions of easily digestible foods rather than large, heavy meals that could cause digestive discomfort. 

Be sure to avoid high-carbohydrate foods immediately after breaking the fast, as they can cause rapid insulin spikes and electrolyte imbalances. 

• First, include high-protein or high-fat foods, and then transition to higher-carbohydrate foods.
• You can include bone broth, light soups, or small amounts of cooked vegetables. These are great options since they are light on the stomach and provide essential nutrients to start nurturing your body.

How Should You Break A 36-Hour Fast Differently?

Consider breaking your fast with a small snack or light meal, then waiting 1-2 hours before eating a full meal. This eating pace allows your digestive system to go back to normal function gradually. And, pay attention to hunger and satiety cues. 

Eating slowly and mindfully can help prevent overeating and digestive issues. 

Read more: Dry Fast vs Water Fast: What to Know Before Trying It

Tips For Fasting The Right Way

Succeeding in your extended fasts requires proper preparation, execution, and the right recovery strategies. 

Here are some tips to help you fast the right way:

• Pre-Fasting Preparation: Before fasting, focus on eating nutrient-dense, whole foods while gradually reducing processed foods and refined sugars.
• Stay Hydrated: Ensure you stay properly hydrated not only during your fast, but also before and after. Consider consulting a healthcare professional to determine if you need to supplement with electrolytes.
• Staying Busy: If you are struggling with the fast, consider staying busy with light activities, work, or hobbies.
• Don’t Overexercise: Avoid intense exercise during extended fasts, since your body may not have enough energy reserves for high-intensity activities. 

Frequently Asked Questions

• Is a 24-hour fast enough?

Yes, 24-hour fasting can offer several health benefits, including improved insulin sensitivity, activation of autophagy, and fat loss. However, it is best to consult with a healthcare professional if a 24-hour fast is suitable for you.

• Can I do 36 hours once a week?

While you could do a 36-hour fast every week, it’s best to do it every 2-3 weeks, especially if you are new to fasting.

• Should I work out while fasting?

You can engage in light to moderate exercise, such as walking or gentle yoga sessions. 

Avoid high-intensity workouts since your body may not have enough energy to withstand them.

• Do you lose muscle on a 36-hour fast?

In most cases, short-term muscle loss is minimal, especially when you practice occasionally. However, ensure you have a good protein intake during your eating periods and limit high-calorie intake. If done correctly, a 36-hour fast can result in weight loss while preserving your muscle mass.

The Bottom Line

The choice between a 24-hour and 36-hour fast will depend on your personal goals, experience level, and lifestyle factors. Both fasts can provide significant health benefits, but they require a certain level of commitment and preparation. 

If you are a beginner, start with a 24-hour fast to build experience and assess how your body reacts to a longer fast. You can then begin to increase 2 hours at a time until you reach a 36-hour fast. 

Remember that consistency matters more than duration. 

Choose the approach that aligns with your lifestyle and health goals, and always prioritize safety over ambition. 

Make sure you speak with a healthcare professional before beginning any extended fasting protocol, especially if you have an underlying health condition or you are taking medication.