Prolonged fasting, extended fasting or water fast…
All of these terms are synonyms for the same thing – a seemingly simple process of not eating for an extended period. Usually, it means no food intake for anywhere from 24 hours to multiple consecutive days.
You might be asking: Why would you choose to “starve” yourself for days? Is prolonged fasting safe? What prolonged fasting results should you expect?
And can we even survive without food and how long can you safely fast?
We’ll dig into this and more below, so keep reading.
Fasting is natural to us. Or at least it used to be…
Fasting has been part of human nature since the beginning of time. Until relatively recently, food was not so readily available. To survive, early humans needed to store energy from food as body fat to survive the times when food was scarce. If the human body did not have an efficient storage and retrieval method of food energy, we wouldn’t have survived until now.
When it comes to fasting length, if you’re a healthy person (with some exceptions, check here), you shouldn’t worry that a few days without food will starve you. The longest-lasting hunger strike in recorded history was undertaken by an Irish political prisoner, Terence MacSwiney. He went for 74 days with no food. Disclaimer… it did not end well for him.
Nevertheless, an average person nowadays is accustomed to regular meals and our bodies are not used to no-food-days anymore. Therefore, we strongly suggest limiting your prolonged fast to a maximum of 72 hours and undergo longer fasts only under medical supervision.
Why would people even put themselves under this challenge of giving up one of the greatest pleasures in our lives – food?
And do it voluntarily for hours…or even days?
Here’s what science says about some of the benefits of prolonged fasting and the prolonged fasting results you could expect.
Your body is designed to have two different states: “fed state” and “fasting state”.
In the fed state, when you are regularly eating, insulin levels are high. During this time, it makes sense to derive the energy from the food that you are eating and store excess calories in your fat cells.
In the fasting state, insulin levels fall. This is the signal for your body to switch energy sources from food to stored body fat from your fat cells and start burning it for energy.
As each of our bodies works differently, the time needed to reach this fasting state also varies. On average, your body will start fat burning after around 17 hours of fasting. However, it can be accelerated by exercise or following low-carb a.k.a. Keto diet before starting the fast.
Bear in mind you will also be skipping around 1500- 2000 calories each day you’re fasting. This means fewer calories for your body to burn, promoting weight management or weight loss.
Just make sure you don’t overcompensate for these lost calories during your periods of eating. A healthy, balanced diet is the key to feel and look your best, no matter what the numbers on a scale say.
Fasting has also shown to increase metabolic rate by 3 – 14%, which translates to an additional 100 – 275 calories burned daily. This effect seems to diminish if you’re fasting longer than 72 hours.
However, while prolonged fasting could result in a few pound weight loss each fasting time, prolonged fasting for weight loss might not be the best long term weight loss strategy. It is not advised to do prolonged fasting more than once or twice per month; therefore some other types of time-restricted eating might be a more sustainable weight-loss strategy.
For example, intermittent fasting 16/8 where you fast for 16 hours and have an 8-hour eating window each day has proven to be an effective long term weight loss strategy. Particularly if you also make sure to have a healthy, balanced diet that fits your weight goals.
Fasting activates autophagy – a process critical for cell health and renewal. During autophagy, cells destroy viruses and bacteria and get rid of damaged structures.
No need for juice cleanses and detox diets, autophagy (the word literally means “self-eating”) is your body’s natural way to do a cleanse.
While there aren’t large human studies done to determine the effects on fasting on life expectancy. A major study on monkeys shows that strict, low-calorie-intake diets could be the key to having a longer, healthier life. Monkeys on calorie-restrictive diets not only lived longer but also had fewer incidents of cancer and cardiovascular diseases.
Many people undergo prolonged fasting due to various mental benefits. It can improve your relationship with food, help appreciate it more or break free from patterns of emotional eating.
However, people with previous eating disorders should be very cautious with any type of fasting as it might have the opposite effect and trigger the old patterns of unhealthy eating habits.
Fasting is part of many religions and spiritual practices and is often practiced to experience increased gratitude, develop self-discipline or even strengthen the faith. The idea is to deny your body its physical needs in order to move the focus away from your body and toward your faith and spirituality.
While it might sound contradictory, often extended fasting supporters report feeling more productive, energized and focused during their fast.
For example, an American entrepreneur and author Tim Ferris practices a 4-day monthly fast that typically begins on Thursday night and ends on Sunday night. As the productivity expert himself says, he normally experiences “some very very clear cognitive benefits,” including more energy and focus.
Obviously, it’s not all fun and games when it comes to drastically changing your eating pattern. After all, your body has been used to your current eating habits which most likely didn’t involve starving it for hours and possibly days.
In a study with 768 people fasting for at least 48 hours, 72% of participants reported at least some side effects with the most common ones being hunger (surprise, surprise), fatigue, trouble sleeping, and dizziness.
Here are 3 important tips to lessen the side effects of prolonged fasting:
While for most healthy people prolonged fasting (up to around 72 hours) poses little health risks, you should consult with a doctor before starting any fasting, especially extended fast, if you.:
Most importantly, remember the good old saying “listen to your body”. Don’t push past your limits and know how to stop when it just doesn’t feel right to keep going.
Fasting, especially for an extended period of time, is not for everyone.
Remember, you’re up for a mental and physical rollercoaster ride.
There will be both periods of sharp focus and extreme sluggishness. Some moments all you can think of will be food or you might be overwhelmed with the infamous “hanger” (a combination of feeling hungry and angry). Therefore, if possible, for fasting pick days without potentially stressful and demanding activities planned.
If you are new to fasting, especially prolonged fasting, it would be a good idea to spend 3 to 4 days preparing your body for the extended fast. Some ways to do so:
Sounds easy right? Still, there are certain important things to note during your fasting time.
Firstly, as mentioned before, stay hydrated! Normally you should follow the rule of 8×8 (8 glasses of eight ounces of water); however, during fasting time it is important to drink even more as you are not intaking water from food.
What exactly can you drink during prolonged fasting?
Your safe drinks with zero calories are:
For more in-depth fasting drinks guide, check “What Can You Drink During Intermittent Fasting”.
If you choose to stick with strict fasting, you shouldn’t consume any food or caloric beverages. However, if a splash of milk in your coffee, a cup of light broth or water infused with fruits/cucumber/mint changes your fasting experience from unbearable to doable, feel free to do it. Some fasting experts, for example, Berkhan from Leangains, allow to consume up to 20 kcal during the fasting period.
While it might be tempting to binge on food right after the fast is over, it is crucial to reintroduce food slowly.
Yes, it might be even dangerous to follow your urge to eat a huge meal.
This is because you may be at risk of refeeding syndrome, a potentially lethal condition in which the body undergoes rapid changes in fluid and electrolyte levels as it digests and metabolizes food after a long period of not eating.
The best is to break your fast with a small meal, smoothie (click for some healthy smoothie tips), light soup or salad. As you feel more comfortable, you can start introducing larger meals throughout the day. For longer fasts, it might even take a few days to feel completely comfortable eating a large meal.
Oh, and hope you’re looking forward to another prolonged fasting benefit: you will have a completely different appreciation for food! Nothing compares to the flavor of food you’ve been craving for days.
Now when you have read about all the pros, cons, to-dos and dont’s of prolonged fasting, it’s up to you whether it sounds like something worth trying.
While it’s often fun and even confidence-boosting to test your mental and physical limits, remember to take care of yourself and don’t exceed your limits. When in doubt, consult with a doctor.
If you are looking for a long term weight loss alternative while still enjoying the food you love, check this 21-day intermittent fasting challenge that has helped hundreds of people successfully lose and sustain (!) their dream weight. Daily 16 hours of fasting will still leave you 8 hours of eating window for you to enjoy healthy and delicious meals. The challenge even comes with a customized intermittent fasting meal plan to ensure you hit your weight loss goal 100%.
We make it really easy for you with our
Fasting Challenges & Meal Plans.
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