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How to Fast for 40 Days? Should You Do It Anyway?

To eat or not to eat – that is the question. The idea of fasting is closely connected to several religious traditions, such as Buddhism, Christianity, Hinduism, Islam, and Judaism.

Fasting is abstaining from food completely or partially for a certain period of time. A fast generally lasts for 12 to 24 hours. 

However, some people attempt a 40-day fast which is incredibly challenging for physical, emotional, and mental health. It’s difficult to imagine days without tasty dishes that fill you with essential nutrients, luscious desserts that make your days a bit brighter, or delicious beverages. 

Some individuals only allow themselves water and non-sugary beverages during their 40-day fasting period.

If you read this article, you will find out about fasting for 40 days. Should you do it? There are potential downsides to 40-day fasting, but is there a safe way to do it? Let’s look at the 40-day fast. 

Can you fast for 40 days without food?

Fasting for 40 days without food may be a personal choice. However, no matter what your reason is – religious or for weight loss purposes – it’s hard to call it a safe method.

There are many factors that impact the length for which a person can survive without food. Fasting for 40 days may be possible without food, but we don’t know for certain. 

Scientists have not studied human starvation extensively for ethical reasons, but some reports have noted that death can occur between 43 and 70 days of fasting (2).

Fasting for a short period of time may be an effective way of losing weight, but here we’re talking about intermittent fasting, not long-term fasting (10). 

Fasting for 40 days with only water can cause extreme changes to your body. When you go without food, your body starts to obtain its energy and fuel from its own fat. Your body needs nutrients from food to survive. It uses carbs, carbohydrates, and fats, in addition to minerals and vitamins to renew cells and fuel vital bodily processes (6).

Therefore, fasting for 40 days without food is not recommended, even for healthy people. 

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Is it possible to fast for 40 days?

Some people are so persistent or goal-oriented that they do extreme things simply to satisfy their needs.
But if you wonder whether it’s possible to fast for 40 days, you should know that it is not considered safe for most people. In addition, the following groups of people should avoid fasting completely: 

  • pregnant and breastfeeding women
  • people with a history of eating disorders
  • elderly people, children, and teenagers
  • people with diabetes who are taking insulin (10).
See also
Can You Have Coffee When Fasting?

Although people have fasted for long periods and survived, others have died attempting long-term fasts. Therefore, it is not considered safe for the majority of people. It may be better to come up with a 40-day fast meal plan that allows some food during the fasting period.

how to fast for 40 days  

A potential alternative option may be intermittent fasting, which involves shorter periods of complete or partial abstinence from eating. There are six methods of intermittent fasting (12): 

  1. Fast for 12 hours per day. This is a good option for beginners as you can plan your fasting window to be overnight. For example, you can choose to fast between 8 pm and 8 am. You would need to finish your dinner before 8 pm and wait until 8 am to eat breakfast, but you would be asleep for most of the fasting time. 
  2. Fast for 16 hours. This leaves an eating window of 8 hours, which is called the 16:8 method or the Leangains diet. Usually during this fast, a person finishes their evening meal by 8 pm and skips breakfast the next day, but you can choose whatever schedule works best for you. 
  3. Fast for two days a week. This fasting includes eating a normal amount of calories for five days of the week and decreasing the consumption of calories on two non-consecutive days. On average, males eat 600 calories and females 500 calories on the two fasting days. 
  4. Alternate day fasting. This entails fasting every other day. Some people avoid solid food on fasting days while others consume a maximum of 500 calories. On feeding days, people choose to eat whatever they want. 
  5. A weekly 24-hour fast. This involves eating no food at all for 24 hours at a time. Some people fast from breakfast to breakfast or lunch to lunch. 
  6. The warrior fast. This is an extreme form of fasting that involves eating very little, just a few servings of raw fruit and vegetables, during a 20-hour fasting window, then eating one large meal at night. Your eating window is approximately four hours.

The last three types of intermittent fasting are particularly challenging. They may cause fatigue, irritability, or headaches. It’s better to start with milder versions before you switch to more extreme versions. 

It’s important to begin your intermittent fasting routine healthily and is best done under the supervision of a doctor. In other articles, we discuss Intermittent Fasting Coffee and Intermittent Fasting Meal Plan Examples

How much weight can you lose on a 40-day fast? 

Many people want to lose weight and consider fasting to be a way of achieving this. However, relatively little research has been conducted on weight loss results after fasting other than intermittent fasting, but there are some studies that have demonstrated the effects of water fasting on body mass. A recent literature review of eight studies on water fasting – a medically supervised fast where people consume only a tiny amount of juice and soup each day – examined how the fast would impact weight loss.

See also
The Simplest Intermittent Fasting Guide of 2023

Fasting produced noticeable short-term weight loss. People who fasted for five days lost approximately 4% to 6% of their body weight; those who fasted for seven to 10 days lost approximately 2% to 10%, and those who fasted for 15 to 20 days lost 7% to 10% (13). Only a few studies followed up to see if the lost weight was regained. In one study, all the weight was regained after 3 months. In two others, participants were encouraged to restrict their calorie intake after the fasts ended and only regained a small amount of their lost weight.

Another case report discussed the starvation of a 34-year-old obese male who voluntarily undertook a 50-day fast with the goal of losing weight. During this time, the man consumed only coffee, water, tea, and daily multivitamins. His initial weight was 96.8 kg and after the 50-day fasting period, he weighed 75.4 kg (2). 

Even if you were able to safely fast for 40 days and experience weight loss, you are more likely to regain the weight once you start eating food again (13). 

So, should you use a 40-day fast for weight loss? The correct answer is no. Losing weight healthily involves eating nutritious food, sleeping well, and leading an active lifestyle. Yes, you have probably heard this many times, but unlike fasting you will not need to worry about potential side effects and risks (spoiler alert, there are many). 

What happens to your body during a 40-day fast?

Long-term fasting, such as for a 40-day period, is not easy for your body. Your body will gradually go through different changes. Here are some potential Fasting Side Effects:

  • Dehydration. The truth is, you don’t only hydrate yourself by drinking water and you get a lot of water from food. With food avoidance, you are more likely to experience dehydration as you’re not getting any fluid or electrolytes from food (5). This is why it’s essential to consume plenty of water and electrolytes not only during the fasting period but also before it. 
  • Increased stress levels and sleep deprivation. Let‘s face it, you find it difficult to fall asleep when you’re hungry (5). In addition, many individuals experience headaches during a fasting period, which affects focus, productivity, and sleep. 
  • Heartburn. Without eating food, you reduce stomach acid that digests food and destroys bacteria. Smelling food or even thinking about it during fasting periods makes the stomach produce more acid, potentially resulting in heartburn (5).
  • Sickness. Longer periods of fasting can lead to headaches, constipation, and irritability. You can reduce these side effects by switching to periodic or time-restricted fasting (1).
  • More weight. Human beings are prone to reward themselves after they have done hard work or fasted. This is why many people overeat on non-fasting days (1). Therefore, people may gain even more calories than they lost during their non-fasting period. 
See also
The Benefits of 40 Hours Fasting: Do They Outweigh The Potential Risks?

Fasting for long periods can lead to starvation and even death. You should consult a doctor before you start any fasting routine. 

Read more: 6 Dirty Fasting Mistakes You’re Making That May Get In The Way of Weight Loss

What are 5 benefits of fasting? 

You cannot reap the non-food 40-day fast benefits as it can be dangerous for you, but if you’re dealing with intermittent fasting for 40 days, there may be potential advantages your body can get. Let’s take a look at five scientifically-backed potential benefits of intermittent fasting. 

  1. It may promote blood sugar control by decreasing insulin resistance. A new study published in 2023 demonstrated that an intermittent fasting regimen produced improved glucose tolerance to a greater extent than traditional calorie restriction after six months, although the differences between groups disappeared after 18 months (8).
  2. It may improve heart health. One review found that alternate-day fasting may decrease the levels of total cholesterol in overweight people (3).
  3. It may help with weight loss. One review found that fasting may be more effective for weight loss than calorie restriction (9).
  4. It may help you live longer. A review in 2021 discussed mechanisms by which fasting can be effective for increasing longevity and delaying disease, although much more research in this area is required  (7).
  5. It may promote better health by combating inflammation. A review in 2022 found that both intermittent fasting and energy-restricted diets may reduce levels of C-reactive protein, which is a marker of inflammation (4).

It is important to note that these potential benefits come from intermittent fasting and not a 40-day fast with only water. The second option may be harmful to you. Instead, you could try intermittent fasting for 40 days and reap the potential benefits after consulting your healthcare provider. 

how to fast for 40 days

What are the safest ways to fast? 

Do you want to feel good during and after fasting? If you do, you shouldn’t fully abstain from food for 40 days. Intermittent fasting for 40 days may be a better option if it is safe for you. Here are six essential hacks for enjoying your intermittent fasting routine without feeling dizzy, hungry, cranky, or sleepy. 

  1. Have short fasting periods. You already know about the six fasting regimens. Start with one of them. Not allowing yourself to eat for 40 days straight and drinking only water will make you constantly feel hungry, irritated, and discouraged. It is also incredibly dangerous. The best way of avoiding this side effect is to stick to shorter fasting periods. 
  2. Stay hydrated. Dehydration can cause fatigue, dry mouth, headache, and thirst, so it is important to consume enough water while fasting (12).
  3. Relax and rest, but don’t get bored. Although strenuous activities are not vital during the fasting period, mild movements such as those in yoga, walking, or meditation may be beneficial (12). 
  4. No feasts after fasts. So, you haven’t eaten for eight hours straight and when it’s time for you to eat, you see no boundaries and devour a mountain of food because you deserve it, right? Wrong! Breaking your fast with a lavish feast can lead to bloating (11) and excessive calorie consumption. Stay cool, and eat a moderate amount of food slowly. 
  5. No thoughts about food. Distract yourself with engaging activities. Take a bike ride around the city, try painting, or meet up with your friends. 
  6. Eat nutrient-dense food after the fasting period. Foods that are high in fiber, protein, vitamins, minerals, and other nutrients help prevent nutrient deficiencies and keep blood sugar levels steady. A balanced diet is the key to weight loss and overall health (12). 
See also
A Beginner Intermittent Fasting Meal Plan to Fit Your IF Journey

In addition, you don’t need to become exasperated if you feel tired or fainted. If fasting constantly impacts your productivity, your sleep, or mood, you should consider stopping the process for some time. 

As previously mentioned, fasting may be challenging for many people, so before you start a fasting regime, you should talk to your doctor, think about the healthiest fasting method for you, and realize your main goals.

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Is fasting for 40 days bad for you?

Fasting for 40 days without food may be dangerous for you. Your body needs nutrients to remain healthy and productive. A lack of these can pose threats to your health: dehydration, fainting, falls, lack of focus, as well as reductions in heart rate and blood pressure. Therefore, it’s better to opt for milder methods of intermittent fasting that allow you to consume food during a non-fasting time. 

See also
Intermittent Fasting Macros – Managing Calories the Smart Way!

What should I eat during 40 days of fasting?

Some people choose to drink only water and juices. Others allow themselves small amounts of food. When it comes to meals, it’s important to focus on nutrient-dense food, particularly vegetables, whole grains, nuts, meat, and fruits. You should limit ultra-processed products, sweet treats, and sugary/alcoholic beverages.  

What happens if you don’t eat food for 40 days?

Not eating food for 40 days can lead to a number of health complications, including bone loss (your bones become weak and thin), muscle weakness and wasting, constipation, feeling sick, dry skin, loss of menstruation (in females), fatigue, tiredness, lack of normal sleep, and feelings of hunger. It could even pose the risk of death.

What is the longest healthy fast?

If we are talking about water fasting, then medical advice suggests around 24-72 hours as the maximum time without consuming food. However, intermittent fasting for weight loss can go on for several weeks or even longer, but a fasting routine is not suitable for everyone. You should always discuss your individual situation with your healthcare provider first.

The Bottom Line

In this article, we have looked at the essence of 40-day fasting and its potential drawbacks. 

You’ve learned that fasting for 40 days without food has been done, but is not safe or recommended. Due to its unethical and harmful nature, scientists cannot conduct research on real people to uncover the effects of long-term fasting on the human body. 

In addition, certain groups of people should avoid fasting altogether (breastfeeding and pregnant females, children and teens, seniors, people with a history of eating disorders, and those who are taking certain medications).
The safer way for those who want to and can fast is trying intermittent fasting, which involves six main methods, some of which are good for beginners while others are for individuals who have already tried the easier methods. 

Losing weight during a 40-day fast is possible but unsafe. In addition, many people who return to their typical eating routines after fasting regain weight. 

Long-term fasting may result in certain health issues, including dehydration, sleep deprivation, increased stress levels, sickness, heartburn, and even death. 

However, if you choose a less severe fasting method under the supervision of your doctor, you may obtain benefits from it. 


This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!


  1. 4 intermittent fasting side effects to watch out for (2023,
  2. Complete and Voluntary Starvation of 50 days (2016,
  3. Effect of alternate-day fasting on obesity and cardiometabolic risk: A systematic review and meta-analysis (2020,
  4. Effects of intermittent fasting diets on plasma concentrations of inflammatory biomarkers: A systematic review and meta-analysis of randomized controlled trials (2020,
  5. Fasting: Health benefits and risks (2015,
  6. How long can you survive without food? (2023,
  7. Intermittent and periodic fasting, longevity and disease (2021,
  8. Intermittent fasting plus early time-restricted eating versus calorie restriction and standard care in adults at risk of type 2 diabetes: a randomized controlled trial (2023,
  9. Intermittent Fasting versus Continuous Calorie Restriction: Which Is Better for Weight Loss? (2022,
  10. Intermittent Fasting: What is it, and how does it work? (
  11. Meteorism (2022,
  12. Six ways to do intermittent fasting (2023,
  13. Water fasts can help you lose weight, but you might gain it back quickly (2023,
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