The 36-Hour Fast: A Practical Tool for Fat Loss

It has been well documented that prolonged water fasting may offer profound health benefits—such as cellular clean-up (autophagy), improved insulin sensitivity, and better overall blood markers. In this short blog post, I’m going to focus on a shorter fast of 36 hours—also known as the Monk Fast—and explore it purely from the perspective of fat loss.

Most published studies show that, in terms of fat loss, reducing calories gradually over the course of a week yields similar results to cutting a larger amount of calories on one day. So when we exclude the additional benefits of fasting, it really just comes down to personal preference. Here are a few reasons why I personally prefer the 36-hour fast over a consistent daily calorie deficit.

Fat Loss, Calorie Deficits & Motivation

Of all the factors that affect successful fat loss, the most fundamental is consuming fewer calories than you burn. This is where the 36-hour fast truly shines. If you’ve reached a good level with tracking your food intake or eating intuitively, you can use this strategy to eliminate an entire day’s worth of calories—then return to eating closer to maintenance for the rest of the week.

I prefer this approach over a daily deficit for two main reasons: First, I find I can push my workouts harder since I’m not constantly low on energy. That leads to better training output and more efficient results. Second, it’s much less mentally taxing. Using a bit more willpower for just one day is easier for me than dealing with small restrictions every single day—especially as the week gets busier with work and life commitments.

It’s also a great way to start the week. You can finish eating on a Sunday evening and resume again on Tuesday morning. This reset creates positive momentum, especially if you’ve overindulged during the weekend. I would recommend, however, that you try intermittent fasting or a 24-hour fast before attempting a full 36-hour fast.

Productivity Boost

It’s widely acknowledged that fasting—especially prolonged fasts—can trigger a state of high productivity. One theory is that this stems from our evolutionary roots. When food was scarce, we needed heightened focus and mental clarity to hunt for our next meal.

What better time to have laser-beam focus than a Monday—the perfect time to tackle the most demanding tasks on your to-do list?

After meals, we often experience sluggishness or even a desire for a nap. Factor in the time spent preparing, eating, and recovering, and lunchtime can eat into a significant chunk of your workday. By skipping meals during your fast, you reduce interruptions and maintain flow state.

That doesn’t mean you can’t take a break—but instead of lunch, opt for a short walk and an espresso. You’ll feel refreshed and ready to finish the day strong.

The Downsides

The biggest trap I see people fall into is thinking that fasting is a magic solution—that it gives them permission to eat whatever they want outside the fasting window. Fasting should be viewed as just one useful tool in the toolbox of a healthy, sustainable nutrition plan.

Another consideration is protein intake. Fasting reduces overall calories and protein, making it a less ideal environment for building muscle. That said, any calorie reduction limits muscle gain, so the question really becomes: Which method best preserves lean mass for you personally?

In my experience, as long as I maintain a consistent resistance training program, I haven’t noticed any muscle loss during extended fasts. Of course, this may vary based on the person and their genetics.

Who Should Be Cautious?

Fasting isn’t for everyone. If you’re new to nutrition tracking, struggle with disordered eating, or have underlying health conditions, I recommend speaking to a healthcare professional before trying an extended fast. Start slow—perhaps with a 16:8 intermittent fast or a single 24-hour fast—before attempting 36 hours.

Also, hydration is crucial during fasting. Drink plenty of water and consider adding electrolytes (like sodium, potassium, and magnesium) to help prevent headaches or fatigue.

Perspectives From a PT

Before we wrap up, it’s worth remembering that if your weight hasn’t changed for a while, you’re likely eating at your maintenance calorie level. Instead of overthinking how to reduce calories, you could keep the rest of your week exactly the same and simply fast for one day.

For example: Let’s take a man who eats 2,500 calories a day to maintain his weight. If he fasts for 36 hours once per week—say from Sunday evening to Tuesday morning—he effectively removes 2,500 calories from his weekly intake. Over four weeks, that’s a 10,000-calorie reduction.

Since it takes roughly 3,500 calories to burn one pound (about 0.45 kg) of fat, this method could result in around 1 kilogram (2.2 pounds) of fat loss per month, without needing to restrict daily intake or obsess over food tracking.

Of course, these are estimates and actual results will vary depending on individual metabolism, activity level, and body composition—but it’s a great example of how simple and effective the 36-hour fast can be for consistent fat loss.

Final Thoughts

The 36-hour fast isn’t a miracle solution—but it’s flexible, practical, and effective for those who are already dialled in with their training and diet. It can help you break through plateaus, improve focus, and simplify your approach to fat loss without constantly counting calories.

If you’re considering giving it a try, ease in gradually, stay hydrated, and make sure it fits your lifestyle. Like any tool in fitness, it works best when used with intention—not as a shortcut, but as a strategic part of your long-term plan.