Benefits And Risks Of A 72-Hour Fast: All You Need To Know

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72 hour fast

72-Hour Fast | How To Prepare | Fasting Properly | How To Break The Fast | Stages | Benefits | Risks | Who Shouldn’t Fast

A health and wellness trend that has been gaining traction over the past few years is intermittent fasting. While there are many formats for intermittent fasting, one of the most extreme is a 72 hour fast

During a 72-hour fast, you abstain from eating any food for 3 consecutive days. This type of fasting has become increasingly popular due to its purported health benefits. But there are also potential risks associated with it. 

We look into this extended fasting program to weigh the benefits and risks so you can make an informed decision. 

Understanding a 72-hour fast

A 72-hour fast is a type of fasting where you abstain from food and consume only water or other non-caloric beverages for 3 days. A stricter variant of this type of fast is also known as a water fast, where only water is allowed.

How to Prepare for a 72-hour Fast

Before starting a 72-hour fast, it is essential to prepare your body and mind for the fast. Here are some tips to help you prepare for a 72-hour fast:

1. 2-3 days before the fast

Start increasing your hydration 2-3 days ahead by drinking water, herbal teas, and other non-caloric beverages at slightly greater levels than normal.

It is also important to reduce your intake of processed, sugary, and high-fat foods during these couple of days. This allows your body to ease-into the fasting program.

Incorporate healthy fats and protein into your diet to help keep you satiated and provide your body with essential nutrients in advance.

2. Mindset and mental preparation

Extended fasting formats can be challenging, both physically and mentally. Mentally preparing yourself can help you stay focused and motivated during the fast. 

3. Planning

It is also important to plan ahead for a three-day fasting. Daily consumption, daily activities, and other factors should be taken into consideration when planning the fast. In the absence of a plan, it can be difficult to stick to the fast and attain the desired results.

How to fast properly?

Embarking on a fast can be a transformative experience, but to reap its full benefits, it is crucial to understand how to fast properly.

What you can/cannot consume during a 72 hour fast

During a 72-hour fast, only water, black coffee, herbal tea, or other non-caloric beverages are allowed. Avoid any calorie-containing liquids, including fruit juices or soda.

Monitor your vitals

During a fast, it is essential to monitor your blood pressure, blood glucose levels, and electrolyte balance. If you have a pre-existing medical condition, it is important to consult with your doctor before starting a fast.

How to break a 72 hour fast?

Breaking a fast properly is just as important as fasting. Here are some tips on how to break a 72-hour fast:

1. Break the fast slowly

Start with small, easily digestible foods like bone broth or fruit. Avoid consuming large meals or heavy, high-fat foods.

2. Foods to eat when breaking the fast

When breaking a fast, it is essential to consume nutrient-dense, whole foods. Some examples include non-starchy vegetables, fruits, lean proteins, and healthy fats.

3. 1-3 days after the fast

After the fast, gradually reintroduce solid foods into your diet over the next 1-3 days. Focus on consuming nutrient-dense foods that are easy to digest.

Stages of fasting: What happens during a 72-hour fast

The duration of the 72-hour intermittent fasting is long enough to trigger certain physiological changes in the body. Let’s take a look at the expected daily changes during a 72-hour fast.

1st day of fasting-Entering ketosis/hormonal changes

During the first day, your body is deprived of all energy sources. Its glycogen stores get rapidly depleted. 

This triggers the body to shift its primary energy source from carbohydrates to fat. This process is known as ketosis. Ketosis is the process behind the keto diet, which is popular among people who aim to lose weight.

The body goes through a roller-coaster of hormonal changes during the first day. Levels of human growth hormone, cortisol, leptin, and adrenaline increase while levels of insulin and ghrelin(hunger hormone) decrease.

Physical symptoms on the 1st day of fasting: As the body enters ketosis, it may experience some symptoms, including fatigue, headache, and dizziness. As the body enters ketosis, some people may experience changes in breath odor or a metallic taste in their mouth. Individuals addicted to caffeine or sugar may experience irritability and mood swings.

2nd day of fasting- Autophagy

As the body enters the second day of deprivation/starvation, it kickstarts the next process of sourcing energy- Autophagy. 

Autophagy is the process of breaking down and recycling cellular debris, damaged organelles, and other harmful materials in the body. This process can improve cellular function and overall health.

Studies have shown that autophagy may have a role in preventing and treating various diseases, including cancer, neurodegenerative diseases, and metabolic disorders. 

Physical symptoms on the 2nd day of fasting: At this stage, hunger pangs have reduced to manageable levels. You may still experience bouts of dizziness or headaches depending on your hydration levels and electrolyte balance. 

3rd day of fasting-Increased insulin sensitivity

By the third day of a 72-hour fast, the body has undergone several physiological changes. 

One of the most notable changes is an increase in insulin sensitivity. Insulin sensitivity refers to how sensitive the body’s cells are to the effects of insulin. 

When insulin sensitivity is high, the body can better regulate blood sugar levels and reduce the risk of insulin resistance and type 2 diabetes.

Physical symptoms on the 3rd day of fasting:  By the third day, hunger pangs have become milder. You may still experience occasional lightheadedness or fatigue due to the lack of nutrients and energy. Additionally, some people may experience digestive issues, including bloating and constipation. Proper hydration during this phase helps alleviate these symptoms.

72 hour fast benefits

Challenging as it may be for many among us, prolonged intermittent fasting has many proven health benefits. 

Here we look at the expected benefits of a 72-hour extended fasting and the scientific rationale behind these benefits: 

1. Ketosis/Weight loss

One of the main benefits of a 72-hour fast is the induction of ketosis, which can lead to weight loss and improved body composition.  

2. Autophagy

Another significant benefit of a 72-hour fast is the induction of the cellular recycling and regenerative process: autophagy. During a 72-hour fast, autophagy is in full swing, which may lead to improved cellular health and longevity.

Autophagy has been associated with a range of health benefits. This includes improvements in the immune system, reduced risk of chronic diseases such as cancer, and prevention of neurodegenerative diseases like Alzheimer’s and Parkinson’s

3. Reduced inflammation

Caloric restriction [1]Cell: Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool through methods like intermittent fasting is known to reduce the incidence of inflammatory and autoimmune diseases

Studies [2]National Library of Medicine: The effects of diurnal intermittent fasting on proinflammatory cytokine levels while controlling for sleep/wake pattern, meal composition and energy expenditure suggest that fasting may lower levels of pro-inflammatory cytokines and increase anti-inflammatory markers, leading to reduced inflammation in the body. 

Additionally, fasting can improve gut health and promote the growth of beneficial gut bacteria. A healthier gut and a better digestive system can further reduce inflammation.

4. Improved insulin sensitivity

Insulin sensitivity refers to the body’s ability to respond to insulin and regulate blood sugar levels effectively

During prolonged fasting, the body is forced to release energy by breaking down glycogen using the insulin hormone. This leads to improved insulin sensitivity, which helps reduce the risk of developing diabetes. 

5. Blood pressure

Fasting can lower blood pressure by reducing oxidative stress and inflammation, which are both known to contribute to hypertension. 

Additionally, fasting can lead to weight loss and improved body composition, both of which have been associated with lower blood pressure. 

6. Improved mental clarity

Fasting for an extended period has been shown to increase the production of brain-derived neurotrophic factor (BDNF) [3]National Library of Medicine: The Impact of Intermittent Fasting on Brain-Derived Neurotrophic Factor, Neurotrophin 3, and Rat Behavior in a Rat Model of Type 2 Diabetes Mellitus, a protein that supports the growth and maintenance of neurons in the brain. BDNF has been linked to improved cognitive function, mood, and memory

Additionally, fasting can promote the production of ketones, which are byproducts of fat metabolism. Ketones can serve as a healthier alternative energy source for the brain. 

7. Increased energy

Some individuals report feeling a surge of energy and increased mental clarity once they enter the state of ketosis. This can be attributed to the production of ketones, which provide a steady source of energy for the body and brain. 

Fasting can also improve sleep quality, which can also contribute to increased energy levels.

8. Slows Aging

Fasting has been shown to activate cellular repair mechanisms, such as autophagy and apoptosis, which can help remove damaged cells and promote the regeneration of healthy cells. Apart from this, fasting can reduce oxidative stress and inflammation. All these factors may slow down the process of aging. 

Risks of prolonged fasting

Despite many benefits of intermittent fasting, it is important to note that a 72-hour fast is suitable for everyone. Here are some potential risks:

1. Dehydration

Fasting without a proper hydration plan can cause dizziness, fatigue, headaches, and disorientation. All of these are signs of dehydration. 

Moreover, since the body starts using up glycogen, it is bound to lose even more water content. After all, each gram of glycogen is bound to 3 grams of water[4]PubMed: Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. This means that during extended fasting the body can lose a significant amount of water weight.

2. Orthostatic hypotension

During a fast, blood pressure may drop, leading to orthostatic hypotension, a condition where blood pressure drops when standing up. This can cause dizziness, lightheadedness, or fainting.

3. Nutrient deficiencies

Prolonged fasting can lead to nutrient deficiencies. This is especially true if the diet before, during and after the fast is not well-planned, balanced, and nutrient-dense.

4. Hypoglycemia

While improved insulin sensitivity is an expected benefit of fasting, some people may experience severe dips in blood sugar levels. It is important to watch out for signs of hypoglycemia and attend to the symptoms immediately.

5. Electrolyte imbalances

Fasting can lead to electrolyte imbalances, especially if hydration is not maintained. This can lead to muscle cramps, fatigue, and other symptoms.

6. Hunger pangs and disordered eating 

Fasting can lead to intense hunger pangs and may trigger disordered eating behaviors in some individuals. People with eating disorders should be especially careful when considering intermittent fasting in any format, let alone 3 day long fasts.

7. Fatigue and headaches

Depriving the body of calories, nutrients, and glucose can cause lightheadedness, headaches, and fatigue. In a normal progression of a 3-day fast, these symptoms must be temporary. It is best to listen to the body’s signals and stop fasting if these symptoms persist.

Who should not fast for 72 hours?

While fasting can be beneficial for many people, there are some individuals who should not attempt a 72-hour fast. These include:

  • Pregnant or breastfeeding women
  • Children and adolescents
  • Individuals with eating disorders
  • Individuals with certain medical conditions, such as type 1 diabetes or liver disease
  • Individuals taking certain medications that require regular food intake


If intermittent fasting is something you are considering and you decide to do a 3-day fast, make sure that you plan ahead and prepare your mind and body for the upcoming challenge. If done safely, a 72-hour fast can provide numerous health benefits that can contribute to your overall well-being.

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