Written and medically reviewed by Nicole Grant, RD
Fasting, in its many forms, has been practiced for centuries and offers a range of health benefits. While extended fasts of 3–7 days have been embraced by some people for their intense and deep cleansing effects on the body, there are inevitable challenges that come along with this practice.
During extended fasting, significant metabolic changes occur as the body adapts to the absence of energy from food. Understanding what happens to your body during a multi-day fast and how to approach it can help you navigate the fasting process and optimize the potential benefits.
However, prolonged fasting isn’t for everyone. So, you may also want to consider a daily, more sustainable fasting routine instead. In this article we will review both so you (and your healthcare professional or a registered dietitian, whom you should consult to assess your individual health status and potential risks) can make an informed decision about what is best for you.
What Is a Multi-Day Fast?
A multi-day fast refers to a period of abstaining from food and caloric beverage intake for three or more consecutive days. (This is also commonly called water fasting.) Participants may only consume water, herbal teas, and possibly electrolytes to maintain hydration and essential nutrient balance. During this fast, the body undergoes significant metabolic changes, including entering a state of ketosis whereby stored fat gets used for energy. The purpose of a 3–7-day fast is often to achieve potential health benefits such as promoting cellular rejuvenation (otherwise known as autophagy), enhancing insulin sensitivity, and facilitating weight loss.
What Happens to Your Body During a Prolonged Fast?
Although everyone is different in their response to fasting, whether it’s their genetics, exercise routine, or what they ate the night before, a general pattern emerges as the body goes without food.
In the initial 0–4 hours of fasting, your body metabolizes the last meal you ingested, utilizing glucose and the hormones insulin, ghrelin, and leptin to regulate energy and appetite. Between 4–12 hours is called the catabolic phase, when the body begins to break down its stored “easy-access” fuel, called glycogen, and depletes the glucose in the liver. At 12+ hours (depending on your fuel stores), the real magic starts to happen. This is when the metabolic switch flips and fat starts to be prioritized as fuel instead of glucose, leading to an increase in fat burn rate and, consequently, amount of fat burned. This is why so many people love a simple 12–16 hour fast!
As your fast progresses, your body remains in a state where it primarily burns fat for energy. It produces ketone bodies, which are a byproduct of fat breakdown, for energy while also creating glucose through a process called gluconeogenesis, which is essential for proper brain function. Hunger levels may increase, creating one potential challenge, but eventually hunger hormone levels start to decline and the body reaches a state of nutritional ketosis.
Does a 7-Day Fast Have Benefits?
Extended fasting periods can lead to improved metabolic health. By triggering the cellular rejuvenation processes of autophagy, promoting fat oxidation, and enhancing insulin sensitivity, fasting can have a positive impact on energy levels and overall health.
Longevity Benefits
Extended fasting periods may boost autophagy — a cellular recycling process that helps remove damaged proteins and organelles — which promotes cellular rejuvenation. Additionally, fasting has been shown to have anti-inflammatory effects, increase stress resistance, and influence various metabolic pathways, which can all lead to a longer, healthier life.
In addition, although research is limited, prolonged fasting has been shown to be helpful as a complementary approach to traditional cancer treatments. A couple studies have shown that fasting before and after a chemotherapy session can result in less chemo-related side effects and better quality of life during treatment.
Improved Metabolic Health
During a long fast, the body undergoes ketosis. In the absence of dietary carbohydrates, the body depletes its glycogen stores and starts burning stored fat as an alternative fuel source. This metabolic shift leads to the production of ketone bodies (hence “ketosis”), which provide energy to the brain and other organs. Nutritional ketosis through fasting has been associated with a range of potential benefits, including improved insulin sensitivity, enhanced fat loss, and increased cellular repair mechanisms, which are all part of improved metabolic health.
Fasting may also offer glycemic benefits due to its impact on insulin sensitivity and glucose regulation. The metabolic shift from using glucose to ketones for energy leads to reduced glucose availability, prompting the body to become more insulin-sensitive. Studies suggest that by enhancing insulin sensitivity, fasting can potentially improve blood-sugar control and reduce the risk of insulin resistance and type-2 diabetes.
Benefits of Shorter, Daily Fasts
Believe it or not, most of these longevity and metabolic-health benefits can also be seen with a consistent daily fast. With fasts as short as 14 hours, researchers have seen improvements in cardiovascular markers, blood-sugar control, and insulin sensitivity, as well as significant weight-loss effects. Similar results can be found in consistent daily fasts of 12–18 hours, and once you hit 17 hours, autophagy signals start turning on.
If you’re looking to burn fat and lose weight, fasts lasting 12–18 hours are an excellent way to see increased fat burn every day, not just during a 3–7-day period a few times a year.
Preparing for an Intermittent Fast or a 7-Day Fast
To get ready for a fast, speak with your healthcare provider, figure out the best timing, and engage in some practices that help get your body and mind ready for the journey.
Consult with Your Doctor
Prior to embarking on a prolonged fasting regimen, it’s crucial to consult with a healthcare professional or a registered dietitian. Fasting can have significant impacts on the body and may not be suitable for everyone, especially individuals with certain medical conditions or eating disorders or those taking specific medications. A healthcare professional can assess your individual health status, evaluate any underlying medical conditions or concerns, and provide guidance tailored to your specific needs.
Choose the Right Time
For longer fasts, it’s important to select a time when you can commit to the fast without major interruptions or distractions. Consider your personal and professional obligations, social engagements, and any upcoming events that may impact your ability to adhere to the fast.
Additionally, assess your current health status and any underlying medical conditions that may affect your fasting experience. You’ll want to choose a period when you are feeling physically and mentally well to give yourself the best opportunity to successfully complete a 3–7-day fast and reap all of the health benefits you can. Timing the fast when you have adequate time for rest and self-care can also support a smoother fasting experience.
If you are new to fasting, this is likely not the time to try out a multi-day fast. Instead, get your body used to fasting by starting with shorter fasts such as a 14:10 or 16:8 protocol (i.e., fasting every day for 14 or 16 hours, respectively). A daily fasting window can provide a bit more flexibility, as it allows you to continue to eat food each day while still offering weight-loss and health benefits.
Start by choosing an eating window that aligns with your most important meals of the day. For example, if you are following 16:8 and enjoy having dinner, then pick a window that includes that meal, such as 12–8 p.m.
Mental Preparation
Mental preparation is essential when embarking on a multi-day fast to help maintain focus and motivation. Start by setting clear intentions and goals for your fast. Understand why you are undertaking this journey. What are you hoping to achieve?
Then, educate yourself about the process and potential challenges you may encounter during the fast. It can also be helpful to gradually transition to fasting by implementing shorter fasting periods or practicing intermittent fasting beforehand to acclimate your body and mind.
Next, build a support system! Inform friends, family, or a fasting community like Zero about your plans, as their encouragement and understanding can provide motivation and added accountability. You might also consider working on mindfulness and meditation to cultivate mental resilience before undergoing a 7-day fast. Finally, approach the fast with a positive mindset and embrace it as an opportunity for growth, self-reflection, and self-care.
Physical Preparation
Proper physical preparation is important before undertaking a prolonged fast to support a smooth fasting experience and ensure the well-being of your body. Start by adjusting your diet to focus on whole, minimally processed foods (if you aren’t already!) at least a few days leading up to the fast.
In addition, the last meal before starting a multi-day fast plays a crucial role in promoting metabolic flexibility and facilitating the transition into fasting. Opting for lower-glycemic food choices during this final meal can be beneficial in quickly shifting the body into a state of using alternative fuel sources. Non-starchy vegetables, lean proteins, and healthy fats are foods that help your body minimize reliance on glucose for energy, thereby expediting the metabolic switch to ketosis and enhancing the body’s adaptation to fasting.
Drink plenty of water in the days leading up to the fast and continue to prioritize hydration throughout the fasting period. For longer fasts, engage in light physical activity, such as walking or gentle stretching, to promote blood circulation, flexibility, and overall well-being. (However, with daily intermittent fasts, your normal exercise routine should be fine and even encouraged to help boost your fat-burning capabilities. So if you like regular vigorous exercise, intermittent fasting might be a better choice!)
How to Do a 7-Day Fast or a 12–18-Hour Fast
During any type of fast, it’s important to prioritize self-care and mindful practices to support your well-being. Here are some recommendations on what to do during the fasting period.
Hydrate
Drink plenty of water throughout the day to stay properly hydrated. This is crucial for maintaining overall health and supporting the body’s natural detoxification processes. In addition, don’t forget electrolytes, which are an essential part of hydration.
Sodium and magnesium supplements are commonly needed during longer fasts, since you won’t be getting them from food, and some people find them helpful during shorter daily fasts, as well. Consult with your healthcare practitioner prior to starting a fasting practice in order to determine if and how much you will need.
Take It Easy at First
For daily 12–18-hour fasts, there is typically an adjustment period as you slowly extend your fasting hours. Rest when needed and don’t push it too hard with exercise until you feel your body is ready to take that on. For longer fasts, allow yourself ample time for rest and relaxation. Listen to your body’s cues and give yourself permission to slow down, take naps, or engage in gentle activities that promote relaxation, such as meditation or deep breathing exercises.
Practice Mindfulness
Use this fasting period as an opportunity to cultivate mindfulness and deepen your mind-body connection. During daily fasts, explore how long you prefer to fast by tuning into your hunger and fullness cues. For both longer fasts and daily fasts, consider engaging in activities like meditation, yoga, or journaling to promote self-reflection, reduce stress, and enhance mental well-being.
Move to Make Your Body Feel Good
Once you get into a consistent 12–18-hour fasting routine, you can start incorporating exercise to help accelerate fat burning and other benefits from your fast. For longer fasts, such as 7-day fasts, move your body if you feel up to it and have medical clearance. Light physical activities, like walking or gentle stretching, are great options. Listen to your body and adjust the intensity or duration of your activity based on how you feel.
Find Fasting Buddies
Connect with others who are also fasting or join online communities or forums to share experiences, seek guidance, and find support. This can help you stay motivated, exchange tips, and overcome any challenges you may encounter. (Zero is great for this!)
Keep in mind that these recommendations are general in nature, so you’ll want to tailor them to your individual needs. Everyone’s experience and requirements may differ, so listen to your body, communicate regularly with your healthcare provider, and make adjustments as necessary.
How to Break a Prolonged Fast
Breaking a multi-day fast requires a gradual and careful approach to allow your digestive system to adjust to solid food intake again. Here are some guidelines to follow:
Start with Liquids
Begin by breaking your fast with liquids, such as teas or bone broth. This helps keep your hydration levels up while preparing your body for digestion.
Introduce Easily Digestible Foods
Gradually incorporate easily digestible and light foods, such as broths, soups, or pureed vegetables.
Begin with Small Portions
pt for smaller portion sizes initially to give your body time to readjust. Listen to your body’s signals of hunger and fullness and eat slowly, allowing your systems to adjust to the reintroduction of food.
Choose Nutrient-Dense Foods
Focus on nutrient-dense foods like fresh fruits, vegetables, proteins, and whole grains as you progress.
Avoid Heavy or Processed Foods
Steer clear of heavy, fried, or processed foods, as they tend to be harder to digest after a prolonged fast.
Pay Attention to Your Body
Be mindful of any reactions or sensitivities as you reintroduce different foods. Monitor how your body responds to each food and make adjustments accordingly.
It’s important to note that everyone’s digestive system reacts differently, so it’s advisable to consult with a healthcare professional or a registered dietitian for personalized guidance on breaking your 7-day fast. These experts can offer specific recommendations based on your individual health needs and ensure a safe transition back to a regular eating routine.
How Often Can You Do a 3–7 Fast?
The frequency at which you can undertake a multi-day fast depends on several factors, including individual health, goals, and personal preferences. It is generally recommended to approach extended fasting regimens, such as a 7-day fast, with caution and under the guidance of a healthcare professional or a registered dietitian. These professionals can assess your overall health, medical history, and specific needs to determine an appropriate fasting frequency for you.
For most individuals, it is not recommended to engage in a 7-day fast on a frequent or continuous basis. Instead, integrating shorter daily fasts is often more sustainable and suitable for long-term health and well-being. Consulting with a healthcare professional can help determine the appropriate fasting regimen for your individual circumstances.
Risks and Challenges
Undertaking a prolonged fast poses various risks and challenges that you should carefully evaluate and prepare for. Risks associated with prolonged fasting include nutrient deficiencies, electrolyte imbalances, impaired immune function, muscle loss, and a slowdown in metabolic rate.
It is crucial to consult with a healthcare professional before attempting longer fasts to assess your current health status, discuss potential risks, and ensure such a fast is appropriate for your specific circumstances. Some 7-day fasters encounter such prolonged hunger and cravings along with the mental challenges that go with fasting, so weigh these considerations when deciding whether to undergo a prolonged fast.
Who Should Avoid Fasting for 3 or More Days?
While fasting can have potential benefits for some individuals, it is important to note that prolonged fasting may not be advisable for everyone. Always consult with a healthcare professional to determine whether it is safe and advisable for you!
Here are some groups of people who should exercise caution or avoid a multi-day fast:
- Individuals with underlying medical conditions. Those with diabetes, hypoglycemia, low blood pressure, eating disorders, kidney disease, liver disease, or compromised immune function should consult their healthcare provider before attempting a fast of 3–7 days. Fasting may require careful monitoring and adjustments to medication or treatment plans.
- Pregnant or breastfeeding women. Proper nutrition and caloric intake are vital during pregnancy and breastfeeding. Fasting for an extended period can deprive the body of essential nutrients and potentially impact the health of both the mother and the baby.
- Children and adolescents. Fasting for a prolonged duration may interfere with their normal growth and development.
- Individuals with a history of disordered eating. Fasting can trigger negative behaviors or thoughts related to food restriction.
- Individuals taking specific medications. Certain medications may require regular meals or can be affected by changes in nutrient intake. It is crucial to consult with a healthcare professional to determine if fasting is safe while taking specific medications.
- Individuals with low body weight or nutritional deficiencies. Fasting for an extended period can further compromise the health of individuals who are already underweight or have nutrient deficiencies.
A Better Alternative to a 7-Day Fast
Prolonged 3–7-day fasts may work for some people; however, they’re not for everyone. A more sustainable approach to fasting is to incorporate shorter, daily fasts into your routine. This method, known as intermittent fasting, fits seamlessly into most lifestyles and can be maintained over the long term, promoting sustainable health improvements. With this approach, a daily fasting window of 12–18 hours is sufficient to enter a state of enhanced fat burning, promote autophagy signals, and improve metabolic flexibility without the intense commitment or potential risks associated with longer fasts.
Moreover, daily fasting encourages a routine that can lead to better eating habits, improved digestion, and a more mindful relationship with food. By focusing on this daily cycle, individuals can enjoy the rejuvenating effects of fasting and still maintain the energy levels needed for their daily activities.
Conclusion
Fasting serves as a bridge to better health and self-awareness, whether through the introspective journey of a 3–7-day fast or a more approachable daily fasting routine. While the former offers a deep metabolic reset, its demanding nature and elevated risks may not align with the needs and lifestyles of many.
Instead, the practicality of daily fasts lasting 12–18 hours stands out as a sustainable alternative that is easy to weave into the fabric of everyday life. This approach balances the discipline of fasting with the demands of a busy schedule and thriving social life, allowing for the benefits of improved metabolism, weight management, and a mindful eating practice without the extensive commitment of multi-day fasts.
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