Types of fasting - intermittent and long term

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People have practiced fasting for millennia. Sometimes it was due to famine, sometimes for religion. Recent research has now shown that there is actually a biological benefit to fasting.

The reason keto folk do fasting is because it is easy for them. Eating a high fat diet keeps people feeling full and curbs the hunger cravings. They can go longer without eating, even forgetting to eat, because their bodies are no longer craving fuel in the form of carbs/sugars. 

But fasting can actually be practiced by anybody and, in fact, you can still lose weight eating the way you normally do by just adjusting your timing. It's just harder for carb eaters because their bodies cries out for more carb foods in the form of hunger pangs. 

There are two types of fasting: intermittent fasting and long term fasting.

Intermittent fasting = less than 3 days

Intermittent fasting is used mostly for weight loss by changing the frequency of eating. You decide on how long you go without eating and then a short 'eating window'. Examples would be:


12/12 - pretty much what most of us do if we eat dinner, sleep, and then eat breakfast 12 hours later. Not very effective

16/8 - eliminate or delay breakfast until 16 hours after dinner and then eat all your meals in the 8 hour window

18/6 - (what I do) eliminate breakfast and delay lunch until 18 hours after dinner. Eating window is 6 hours.

20/4 - 4 hour eating window

OMAD - One Meal a Day - So basically a 24 hour fast 

36/12 - Eat dinner, nothing on the next day, eat all day starting with breakfast on the following day, fast again the next day, repeat

5/2 - 5 days of eating normally and 2 days of eating only 500 calories. You can pick which two days.

Those are the most common. Keep in mind I mentioned breakfast as the most often eliminated, but you can tweak it to suit your lifestyle. Maybe skip dinners and only do breakfasts and lunch.

Intermittent fasting has proven to be effective for weight loss in numerous studies. While it is not necessary to be on keto to do it, keto makes it easier - no hunger pangs. 

Long term fasting = 3 days and more

Did you know there was a man who actually fasted for 382 days straight? That's more than a year! He did it for weight loss and health and went from 456 lbs to 180 lbs. Obviously that's not what we are talking about. The most common long term fast is 7 days.

Why fast that long? It turns out that after 3 days your body goes through a process called autophagy. 

"Autophagy is a normal physiological process in the body that deals with destruction of cells in the body. It maintains homeostasis or normal functioning by turnover of the destroyed cell organelles for new cell formation. During cellular stress the process of Autophagy is upscaled and increased."

Basically, your body realizes something is going on and so starts a process of cleaning house by ridding itself of old, diseased, tired cells and generates fresh, new cells. It's your body's own natural cleanse and it's thought that that's the reason cultures over the centuries practiced fasting as a health method. It also slows the aging process by creating fresh cells. 

During fasting your ketone levels are ramped up high to eat your body fat to compensate for the lack of food intake. Ketones are also linked to improved brain function.

Ketones are burned using different pathways and enzymes than sugar, causing a cascade of effects that improve brain health. Let’s go over some of the ways that ketone bodies benefit the brain:

• Ketones are a neuroprotective antioxidant. They have been found in many animal models to act as an antioxidant, preventing harmful reactive oxygen species from damaging brain cells.
• Ketones are a more efficient energy source than sugar. Ketone bodies, beta-hydroxybutyrate in particular, are a more efficient source of energy per unit oxygen than glucose. Burning ketones may be an essential part of maintaining the health of aging brain cells because brain cells tend to lose their ability to use glucose efficiently as fuel over time.
• Ketones increase mitochondrial efficiency and production. The ketogenic diet causes a coordinated upregulation of mitochondrial genes and genes involved in energy metabolism while stimulating the biogenesis of mitochondria. Altogether, this enhances the capacity of brain cells, protecting them from strokes and neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease.
• Ketones increase GABAergic tone and decrease glutamatergic tone. Glutamate, the brain’s main excitatory neurotransmitter, is the precursor for GABA, the brain’s main inhibitory neurotransmitter. Glutamate is essential for neural communication, memory formation, learning, and regulation, but in certain conditions, glutamate can become excitotoxic. In other words, nerve cells can become damaged or killed by excessive stimulation of glutamate, which sets the stage for a variety of issues like multiple sclerosis, Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), and Parkinson’s disease. Although the mechanisms are unclear, ketones have been found to decrease glutamatergic tone and increase GABAergic tone, which helps prevent brain cell damage and improve function.
• Ketones trigger the expression BDNF. BDNF or Brain-derived neurotrophic factor is a protein that acts on specific neurons in throughout the nervous system. It helps to support the survival of existing neurons while encouraging the growth and differentiation of new neurons and neuronal connections. Ketones have been found to trigger the expression of BDNF in ways that can improve the function of the hippocampus, cortex, and basal forebrain—areas of the brain, which are vital in learning, memory, and higher thinking.

(Courtesy of https://www.ruled.me/3-reasons-keto-better-for-brain/)

As you can see, there are many reasons to consider fasting, whether on keto or not. 


Best resource on fasting is Dr. Jonathan Fung, the preeminent expert on the subject. You can watch his lectures on Youtube or get this book, it's an easy read.