72-Hour Water Fast: What No One Tells You About It

The title “72-hour water fast” can scare some people. How can someone go 3 entire days without food? Is it even doable?

The truth is that it is possible, but it’s not for everyone.

People choose to do water fasting for different reasons. 

Some people practice fasting for religious purposes, while others do so for purported benefits, such as weight management or general well-being. 

If you’re considering water fasting, it’s essential to understand both the potential benefits and risks. You should also learn what to consider before attempting it.

This guide provides comprehensive information on 72-hour water fasts, including their benefits and considerations for water fasting. 

Let’s learn more!

What to Know Before a 72-Hour Water Fast

You should acknowledge all the protocols before you consider 72-hour water fasting for yourself. It may be harmful for some individuals, such as those in these categories (1):

• Rely on medications that must be taken with food
• Have certain health conditions.
• Currently pregnant or breastfeeding.
• Are underweight

Talk to a healthcare professional before attempting a fast to discuss whether it is appropriate for you. Consider avoiding very hot weather, which may make fasting more challenging and can increase the likelihood of dehydration (2).

Moreover, here are some tips to follow when adopting a water fasting routine:

Prepare Your Body

Before the fast, ease into it by gradually reducing your calorie intake and cutting out ultra-processed foods, alcohol, caffeine, and added sugar. 

Consider eating light meals, primarily fruits, vegetables, whole grains, and other whole foods, for at least 1-2 days before you start.

Stay Hydrated

Drink plenty of water throughout the fast, at least 2-3 litres daily. 

You can also add a pinch of salt or electrolytes to your water to help maintain mineral balance and avoid lightheadedness or muscle cramps (3).

Listen To Your Body

During the fast, it’s normal to feel tired or hungry in the first 24-48 hours. But if you feel dizzy, faint, extremely weak, or confused, it’s vital to stop the fast and eat something. 

Don’t ignore these warning signs.

Avoid Heavy Activities

Keep physical activity light. Go for walks, do gentle stretching, and get plenty of rest. 

Avoid intense workouts or demanding tasks that could drain your energy.

Caution: Fasting is not for everyone. It should be done carefully and not repeated too often without proper guidance. Always talk to your healthcare provider first.

Does A 72-Hour Water Fast Reset Your Gut?

Fasting gives our digestive system a break from the usual food processing. 

This food break might help reduce inflammation and repair gut damage.

Changes in the gut lining can vary depending on:

• Your age
• Gut condition
• General health
• Eating habits

In most cases, experts state that your gut starts to repair itself within a few days because the cells in your intestines renew quickly (every 5-7 days). 

This gut reset may alleviate minor issues and strengthen the gut barrier, and it happens even when you aren’t fasting (4).

Some believe that fasting aligns with the natural cycle of gut cell renewal and supports deeper repair. However, intestinal cell renewal is not dependent on extended fasting.

Read more: 50-Hour Fast: What to Know Before Trying It

What to Know About Longer Fasts and Gut Health

Apart from giving your gut the much-needed reset, fasting may also influence the diversity and composition of the gut microbiome. 

The microbiome contains trillions of microorganisms that live inside our gut. 

The gut microbiome includes many types of bacteria that play a role in digestion and your gut working well. 

Fasting, even for shorter periods, might support this by helping good bacteria grow and reducing harmful ones (5). However, this complex relationship requires further research for us to understand it thoroughly.

Explaining Migrating Motor Complex

The migrating motor complex (MMC) is a natural cleaning process in your digestive system that happens every 90-120 minutes when you’re not eating. 

It helps move leftover food and waste through the gut.

When you’re eating constantly, this cleaning cycle gets interrupted. 

But with a 72-hour water fast, the MMC has more than enough time to do its job correctly. 

This process can help:

• Reduce harmful bacteria
• May influence gut health (6).
• Clear out undigested food.

More than anything, a water fast can be a chance to break out of unhealthy eating patterns and start fresh with better food choices once the fast ends. Remember that everyone’s gut differs, and fasting isn’t a one-size-fits-all fix. If you have digestive issues or a medical condition, consider consulting a doctor before trying an extended fast.

What Happens To Your Body If You Fast For 72 Hours?

Modern medicine does not widely acknowledge or support water fasting, so it has no official protocol. Some people fast for 1 day, while others extend it to 3 days. 

Regardless, pinpointing the exact stages of fasting can be challenging because individual physiological responses may vary.

That said, here’s what most research says about what happens in your body when you fast for 72 hours:

First 4 Hours (Stage 1)

Right after your last meal, your body still uses the food you ate for energy. 

You’re in the “fed state” (7). This state is the point where your body is busy digesting and absorbing nutrients. 

You probably won’t feel hungry during this time.

4-12 Hours (Stage 2)

As your body finishes digesting, it starts to look for more energy. 

It begins using stored carbohydrates (called glycogen) from your liver and muscles (8). 

This process depends on your last meal and how active you are. If you had a carb-heavy meal, your glycogen can last longer. At this stage, hunger might kick in as your body starts switching gears.

BetterMe: Health Coaching app can help you build a more structured approach to your wellness routine with meal plans, workouts, and habit-tracking tools. Start using the app to explore options that may support your personal fitness and nutrition goals.

12-48 Hours (Stage 3)

This stage is when things start to change. Your glycogen stores are running low, and your body burns fat instead. This shift is often called the “metabolic switch.” 

As fat breaks down, your liver turns it into ketones, which your brain and body use for energy (9).

You might feel tired, get a headache, or feel nauseous. These symptoms are typical as your body adjusts. Autophagy may also begin, where your cells clean out old or damaged parts to recycle them.

48-72 Hours (Stage 4)

Now your body is likely in a mostly fat-burning mode. 

It slows down metabolism to save energy and focuses only on the most critical functions. The fat-burning and cell-cleansing processes from the earlier stage may become even more active (10).

If you’re wondering how long should you water fast, it depends on your goals and health status. A 72-hour fast is intense and not for everyone, so consider talking to a healthcare provider before trying it.

How To Do A 72-Hour Water Fast Correctly?

A 72-hour fast means you’ll go 3 days without eating. It can be tough if it’s your first time, so preparing and planning carefully is important.

Here’s how:

Prepare Your Body First

Don’t jump straight into a long fast if you’ve never done one. Start by cutting back on added sugar and ultra-processed foods a few days earlier. You can also try shorter fasts, like 12 or 24 hours, to get your body used to the idea.

Stay Hydrated

Drink plenty of water throughout the day. Don’t wait until you’re thirsty. You can also add a pinch of sea salt to your water or take electrolytes (without sugar) to avoid dizziness, cramps, or fatigue.

Take It Easy

Avoid heavy workouts or stressful situations while fasting. Try light walks, gentle stretching, or just rest. Your body is already working hard internally, so don’t push it too much.

Listen To Your Body

If you feel lightheaded, weak, or sick, it’s okay to stop the fast. Fasting isn’t a competition. Your health always comes first.

Break The Fast Gently

How to break a 72-hour fast?

After 72 hours, don’t go straight for a big meal. Start with something light like bone broth, a smoothie, or steamed veggies. Give your digestive system a chance to wake up slowly.

Doing a 72-hour water fast might have water-fasting benefits and prolonged fasting benefits, but one must practice it carefully. Go slow, stay hydrated, and be kind to your body throughout the process.

What Day Is The Hardest During A 72-Hour Water Fast?

When you know which day is the hardest during a 72-hour fast, you can prepare yourself for what’s coming ahead. In most cases, it’s the second day when people feel like they can’t go on any longer. 

It happens because:

• By this time, your body has used up most of its quick energy (stored carbohydrates) but hasn’t fully switched to burning fat yet. This period can leave you feeling low-energy, dizzy, or moody.
• Your hunger hormone (ghrelin) may spike, particularly around meal times when your body expects food (11).
• Some people feel headaches, fatigue, brain fog, or nausea as their body adjusts.
• You’re still far from the finish line, so that motivation can dip.

Things may get better on the third day. Many people report feeling surprisingly better, more clear-headed, and less hungry as their bodies start running more efficiently on fat and ketones. Energy stabilizes, and even moods improve.

So if you’re fasting and struggling on Day 2, hang in there. It’s often the final hurdle before things get easier. Ensure you’re hydrating, resting, and paying attention to your body. However, if you’re feeling dizzy, lightheaded, or fatigued, you should consider stopping the fast.

Read more: 36- vs 48-Hour Fast: Which One Should You Do?

Does Autophagy Continue After 72 Hours Of Fasting?

Yes, autophagy may continue after 72 hours. Some believe it can become even more intense.

Autophagy doesn’t turn on like a light switch. It’s more like a dimmer that gradually brightens the longer you fast. Research is still ongoing, but experts sometimes suggest that autophagy usually ramps up after approximately 16 hours of fasting, but doesn’t reach its full effect until somewhere between 36 and 72 hours (12)(13).

At this point, one should acknowledge that fasting cannot continue forever. 

Eventually, if fasting continues too long, your body may start breaking down muscle or slowing vital functions. You should only do longer fasts under medical supervision. 

Remember, the signs to stop water fasting and what not to do while water fasting to ensure you stay on the right track.

So yes, autophagy can continue beyond the 72-hour mark, but it’s important to fast responsibly and prioritize your well-being.

Do You Gain Weight Back After 72-Hour Water Fasts?

As we mentioned, there’s little research on what happens when you fast for 72 hours and after that. However, our limited evidence suggests it’s pretty likely for one to regain any lost weight once they return to normal eating after fasting for 3 days.

A review of 8 studies looked at water fasting and a similar method called Buchinger fasting. These approaches involve going without food, or consuming minimal calories, for several days.

The review reported short-term changes in body weight, but the findings varied by fasting duration and did not establish lasting health outcomes.

In one study, people regained all the weight they lost within 3 months. 

Only a little weight came back in a couple of others, but those people kept their calories low after the fast. 

Varady also pointed out a concern: Two-thirds of the weight lost during these fasts was from muscle, not fat, which isn’t ideal. Without protein, the body starts breaking down muscle for fuel.

She concluded that although you can water fast under medical supervision with no serious adverse events, it requires a lot of effort and doesn’t produce lasting results (14).

What Not To Eat After A 72-Hour Water Fast?

After a 72-hour water fast, avoid heavy, greasy, or highly processed foods. 

Stay away from:

• Fried or fatty meals
• Sugary desserts or drinks
• Large portions of meat
• Dairy-heavy dishes
• Spicy or acidic foods
• Caffeine and alcohol

Start with light, easy-to-digest foods like bone broth, steamed veggies, or a small smoothie to gently wake up your digestive system. Then move on to other nutritious foods as tolerated.

Whether you’re just starting your fitness journey or looking to add more structure to your routine, BetterMe offers tools that can support different wellness goals. Explore the app and see how its workout, nutrition, and habit-building features can fit into your lifestyle.

FAQs

• Does a 3-day fast ruin metabolism?

Not at all. One-time fasts, such as a 3-day water fast, likely won’t have a lasting impact on your metabolism. With very long-term or repeated extreme fasting, metabolism might start to slow down. So don’t worry, your metabolism won’t be “ruined” after one fast.

• Can I work out while fasting for 3 days?

You can, but it depends on how your body feels. Light movement, such as walking or stretching, is usually fine. However, intense workouts may be difficult during a 3-day fast.

• Can I chew gum while fasting?

Technically, it depends on the gum. If you have sugar-free options and only a piece or two, most people are fine and won’t break your fast. But if you’re chewing a lot or the gum has sugar, it might cause an insulin response.

• Does sleeping count as fasting?

Yes, absolutely! Sleeping is a natural part of your fasting window. 

So when people say they fast for 12 or 16 hours, part of that includes their sleep time. 

It’s the easiest way to fast without even thinking about it.

The Bottom Line

A 72-hour water fast is a substantial change to eating patterns and may not be appropriate for everyone. Any short-term changes should not be treated as lasting outcomes.

If you’re curious, ease in, listen to your body, and don’t exceed your limits. And if you have any health conditions or take medication, always check with your doctor first.