Advanced Biohacking: Extended Fasting

by John Limansky, MD August 08, 2018 5 min read

Advanced Biohacking: Extended Fasting

If you have experimented with short term intermittent fasting, as detailed in our Biohacks You Can Start Doing Today: Intermittent Fasting guide, and experienced its many benefits, you may want to take the practice further and amplify the benefits even more. Longer term fasting is more challenging than intermittent fasting, but it also greatly increases the positive effects, so the challenge is absolutely worth the effort.

Generally any fasting period that lasts at least three days without any food consumption is considered long-term fasting. Many of the most powerful benefits of fasting can’t be fully achieved with shorter fasts. For example, after roughly 36 hours of fasting your body will have burned through all stored glucose and glycogen, meaning it is running entirely on stored body fat. In this state you will lose weight rapidly, and burn as much as a half pound of body fat in 24 hours. Similarly, the regeneration of your immune system that fasting triggers doesn’t fully kick in until around 72 hours of fasting, at which point your body is able to regenerate it’s own immune system by a process called autopaghy.  Autophagy is an extremely powerful tool our body uses to remove old dysfunctional cells through the process of apoptosis or cell death. Once your body has been able to clean out the garbage, the new cells are ready to be made.

Extended fasting is perfectly safe for most people, but it can be physically intense and demanding. It’s generally best to start with intermittent fasting, and slowly build up to longer fasts once you’ve become used to the process. For most people, a program of regular intermittent fasting, with occasional longer fasts every few months is the best approach to incorporating long-term fasting into your lifestyle. The following are some of the most popular methods for long-term fasting.

Water Fasting

Water fasting is the most traditional and simple type of fasting, and it is likely the most effective – but also the most challenging. As the name suggests, it involves completely abstaining from food and consuming only water for three to five days. It’s helpful to prepare your body for a water fast by gradually reducing your food intake over several days leading up the fast.

A modified version of the water fast allows coffee or tea in addition to water, as long as you don’t add anything such as cream, sugar, or honey to the beverage. The caffeine and antioxidants in tea and coffee can help alleviate the the lethargy and brain fog that some people experience with water fasting, particularly those who are new to the practice. But be aware that caffeine has a dehydrating effect, and both coffee and tea have additional diuretic effects, meaning they cause your body to excrete more water. So if you choose to consume either, be sure you are taking in plenty of water to stay hydrated.

Whether your choose a true water fast, or a modified fast that includes coffee or tea, you should supplement with electrolytes to ensure proper organ and muscle function. Normal dietary sources of sodium, potassium, magnesium, and calcium are absent in a water fast, but your body needs these electrolytes, so they should be obtained through supplements or himalayan sea salt under the tongue will help keep your electrolytes in balance as well. And when you transition back to normal eating after a water fast, be sure to slowly reintroduce simple, easily digestible foods such as broth, soup, and soft cooked vegetable. Resist the temptation to immediately eat large meals and heavy foods such as meat, fish, and dairy, as eating these foods immediately after an extended fast can make you sick. The reintroduction of high quality ingredients is essential to give your body the appropriate building blocks it will need to regenerate new cells.

Bone Broth Fasting

Bone broth is a broth made from simmering animal bones and sometimes vegetables. Traditionally it has been used as a base for soups and other dishes, but there are plenty of benefits to this tasty and nutritious broth all by itself.

A bone broth fast involves consuming only bone broth and water for three to five days, and you can have as much broth as you like during the fast. This type of fast can be a good alternative to a water fast, if water fasting is simply too daunting of a proposition. Many people find it much less challenging than a plain water fast, and it provides many of the same benefits.

Bone broth is an excellent choice for fasting because it is inexpensive and simple to prepare in large quantities, and it has numerous nutritional benefits. It’s rich in amino acids, trace minerals, and collagen, and may help boost the immune system, alleviate irritable bowel syndrome, improved joint and skin health, and promote gut health. So even when you aren’t fasting, it can be an excellent addition to your every day diet.

As with all the other foods you consume, make sure to use high quality, organic, pasture raised bones as the toxins tend to accumulate in the bone marrow and fatty part of the animal. This will help avoid having those toxins seep into your delicious bone broth.

Exogenous Ketone Fasting

If you’ve followed the ketogenic diet, then you are familiar with ketones. They are the energy source your body uses when it has exhausted its supply of glucose and glycogen, entering a state called ketosis. Your body naturally enters ketosis after a period of 3-5 days of fasting, but by supplementing your fast with exogenous ketones, you can ease this transition.

Exogenous ketones are ketones taken as a supplement, as compared to endogenous ketones which are produced by your body. At the beginning of longer fast, your body won’t be in ketosis (unless you’ve been on the ketogenic diet), so it won’t be able to easily use stored fat for energy. This can lead to some of the negative side effects of fasting like tiredness, hunger, and headaches. Taking exogenous ketones for a short period of time can boost your ketone levels until your body is producing enough on its own.

During a ketone fast, you will consume nothing but water, electrolytes, and ketones. Typically you’ll take the ketone supplement three times daily for the first two days and twice daily for the third and fourth days. By the fifth day your body should be fully in ketosis and producing enough ketones on its own, so you shouldn’t need the supplements.


John Limansky, MD
John Limansky, MD