person holding red and beige twin bell analog alarm clock
You certainly will become a clockwatcher on some forms of the IF approach. After a while, will time fly? Photo by Malvestida Magazine

Unlocking the mystery of intermittent fasting: Fad or phenomenon?- UPDATED for “Intuitive Fasting”

If I were to compare intermittent fasting to a celebrity, I would go with Lady Gaga. It seemed to explode on the scene out of nowhere, but didn’t succumb to being a fad or a one-hit wonder. It’s been timeless  – but it has attracted a lot of controversy. Lately, I came across the “Intuitive fasting” craze pushed by Gwyneth Paltrow, so I investigated and updated this post.


What’s the skinny?

  • In this article, I will break down intermittent fasting, biohacking, and all you need to know about the different approaches to “IF”.
  • It is “lifestyle,” more so than a diet. The benefits are related to weight loss, but also extend to the body’s ability to cleanse and renew itself.
  • It is a highly visible trend embraced by almost every kind of celebrity personalities – CEOs, actors, singers, and media personalities.
  • As famous as it is, it is also infamous, attracting criticism and near ridicule.
  • In this article, I will try to show both sides, then let you decide for yourself.

What it is

IF has been on the scene for a long time, but really reached its peak popularity in 2016 after the publication of several books and documentaries on the topic, which I have linked below. Then, Silicon valley executives like Jack Dorsey and celebrities like Kourtney Kardashian  become walking talking ads for the approach, cementing its status as the “it” lifestyle .

Particularly, in Silicon Valley, IF forms part of a widely controversial form of “biohacking”, which basically just means  following certain routines to live better and longer lives. Dave Asprey, the Silicon-valley based author of the Bulletproof diet, is credited with founding this concept. As part of that lifestyle, according to its proponents, fasting can contribute to faster cell regeneration, longer life, and yes, weight loss. 

Thus, advocates of IF maintain it is not solely a weight loss “diet”. It’s a lifestyle. In a nutshell, the IF in the sense we understand it today takes that natural fasting state up a notch by extending the fasting period and reaping the benefits of the body’s reaction to being in that fasted state. It’s also a natural way of cutting calories, simply by eliminating meals or having a smaller eating “window.” 

The beauty of IF is that there isn’t just ONE prescribed way to do it. There are many ways to approach IF, which gives people options to figure out what works best for their lifestyle. In the “how to follow” section, we will examine the different approaches to IF.

How IF works

The basic premise is that by going for extended periods between eating meals will increase your insulin resistance – remember, we talked about this in the Keto diet. By doing so, your body will be relying on fat for energy until it is in its next “fed” state. Your body is designed to vacillate between “fed”and fasted. In a fed state, insulin is elevated, which signals your body to store excess calories in your fat cells. In the fasted state, insulin is low, which means that the body can burn stored body fat. IF capitalizes on the fasted state of your body.

In the general version of IF, your actual foods are unrestricted. But there are some permutations below, like intuitive fasting that we will discuss.

That’s not the only benefit, however. In fact, a Japanese scientist won a Nobel prize in 2016 for his research on how cells recycle and renew their content, a process called autophagy. Fasting activates autophagy, which at basic level, is like a massive deep cleaning of your body’s cells. This process, which occurs when cells unencumbered with digestion are able to shut down, includes destruction of viruses and bacteria. It’s a process that is critical for cell health, renewal, and survival.

This article gives a helpful 5-stage summary of how intermittent fasting works, and how your body reacts during each stage.

The IF windows

How to follow IF depends on what kind of fasting regime you follow. There are a variety of permutations in approach to IF. In general, you have two “windows” of time in this diet – your eating window, and your fasting window. During the fasting window, it literally means FAST. No chewing gum (not even sugarless), no juice, no diet soda, no food, obviously. 

During the feeding window, IF does not officially restrict your diet. This is why it is often not called a ‘diet.’ However, because of the insulin resistance benefit I spoke of earlier, it’s not a surprise that many people pair IF with a low-carb or keto diet to accelerate the results. 

woman in black long sleeve shirt
The equation of what the perfect fasting approach is in the eye of the beholder. Photo by John-Mark Smith

Different types of IF

I will review the most popular IF methods here. A lot of them will bring back haunting memories of mathematic ratios in AP Algebra.

The latest trend: Intuitive fasting

Intuitive fasting is based on a book by Dr. Will Cole and has recently been touted by Gwenyth Paltrow. Unlike traditional fasting, however, it has dietary restrictions primarily based on the ketotarian diet (you can head to my keto post to find out what that is – it is in fact what it sounds like – a non-dairy, non-animal product Keto diet.

Dr. Cole’s version of IF starts with a 4-week plan premised on “metabolic flexibility,” but ironically, this diet is anything but. The meal plan is pretty restrictive and according to one dietitian, doesn’t even put the body in true ketosis. Dietitians are basically trashing this diet and calling it out for hijacking the intuitive eating, which specifically has a non-diet approach. (You can read my post introducing intuitive eating here.). Check out the video by Dr. Abby Sharp below, where she really breaks it down and comments on each piece of it. If you are interested in trying it, I am not here to stop you, so I linked the book below in the list of resources. Even just reading the reviews is entertainment!

YouTube player


The most mainstream form of IF is the 16:8 approach. This involves a daily fast of 16 hours and an eating ‘window’ where two meals are usually consumed. This can also be adjusted to a shorter fasting window, for example, 14:10, or one can start there and progress.  Experts often recommend 14:10 for women, due to their different body chemistry.

There are variants with even shorter windows, like 20:4, 22:2, etc. Often it is recommended to just start with a 12 hour fast, and see what your body can tolerate from there. 12 hours is technically enough time to trigger the autophagy process, so sticking with this at a minimum consistently is said to lead to results.

You can choose the times of day you would like to eat, so for example if you are a breakfast person, you can have breakfast at 8am, then lunch at 330.  Then you would fast from 4pm until 8am the next day. Many people like to structure their fasts so that they can eat dinner with their families or be social. In this case, if you finished eating dinner at 8pm, you would fast until 12pm the next day. Many people think this is much easier, as you are essentially only skipping breakfast.


The 5:2 diet was popularized by British Doctor and Journalist Michael Mosley in 2012.  The basic setup as its name implies is that you eat normally five days a week followed by two days where you only eat around 500 calories (600 calories for men). 

Recently, there were findings that 800 calories on fast days reap the same benefits – so the diet became more flexible.

I first saw the results of the diet  when my aunt Sarah in England was on the diet  After having three kids almost back to back over 5 years, she always complained about not being able to lose the last 30 pounds of the baby weight she had gained no matter what diet she tried or how much she exercised.  I watched with awe as she ate “normal” meals most of the days, including shortcake biscuits at teatime, bread, and chocolates (English are very fond of their tea and biscuits). On her “2” days, she would come home from her nursing job and heat up a chicken breast with some broccoli. She told me it was easier to do the “2” days when she was too busy enough to sit down and eat. She was literally having her biscuits and eating them too. 

In a recent interview with Men’s Health, the founder of 5:2, Michael Moseley, supported the 5:2 diet’s ability to trigger autophagy, which as we talked about earlier is integral to the body’s cell renewal process.

Accelerating the 5:2 – the 800 diet

The same doctor who developed 5:2 also developed an accelerated form of the diet called the “Fast 800.” On this diet, you would eat 800 calories a day for two weeks, and then transition to 5:2. As a result of this approach one can lose as much as 14 pounds in the first two weeks. He has a meal plan, including 3 meals and a snack, you can access here.

24-hour fasts 

This approach entails a weekly one or two day fast, even up to three days. with normal eating days between. It’s a more extreme approach of the 5:2. It is meant to cleanse the body and help it reset. People on this diet plan can have water, tea, and other calorie-free drinks during the fasting period.

WHY would someone fast for 3 days? Jack Dorsey, the CEO of Twitter, does it every weekend (and only eats dinner the other days of the week). tweeted about it. That period of time is supposed to be when your immune system can reset and cell regeneration can occur. Effectively, your body can hit a “reset” switch. This is possible by letting your body go through the regeneration process unencumbered by processing food.

More about the 3-day fasting experience.

woman about to slice the cheese on wooden board surrounded with bread and sausages
Breaking a Warrior diet fast can mean as much as 3,000 calories in one sitting. Photo by Sigmund

The Warrior Diet

The Warrior Diet was created in 2001 by Ori Hofmekler, a former member of the Israeli Special Forces, who transitioned into the field of fitness and nutrition. As its name implies, the warrior diet is pretty intense. For 20 hours of the day, you either fast or eat very little of low-calorie, simple foods, like hard-boiled eggs, broth, or raw fruits or vegetables. Then, during the 4 hour window, there are phases of foods designed by week. During the first week, salads with healthy fats, veggies, beans and grains are encouraged, then it gradually transitions to incorporating animal proteins. Some people take it to the extreme and just fast for the 20 hours, or even do a 22:2 fast. You can read more about the Warrior diet here.

This type of diet is the source of the pictures you see on instagram of food people are about to house that looks like it’s enough for an army, as their one meal. Some have even achieved fame, like Instagram star and really buff and lean trainer  King Schratz (born Dave Schratz) who sits down in front of his 62,000 Instagram followers to eat his first, and only, meal of the day. This usually includes a variety of burgers and fries, subs, wings, and pasta. Literally a walking, talking ad for Sonic.

black ceramic teacup on table
A cuppa can help you curb your appetite (but no flat whites!) Photo by John-Mark Smith

What you can consume 

On all of these diets, for the most part during the feeding window, the sky’s the limit. You can eat whatever your heart desires. Although these aren’t hard and fast rules, many fasting gurus recommend that one break a fast with low-sugar high healthy fat meals to ease the system into eating.  This would be opposed to having a sugary snack or drink, which after not eating for an extended period would cause an immediate blood sugar spike.

During your fasting window, the options are of course very limited, though can aid in suppressing hunger. Water, green tea, and black coffee are about all the options that you have (unless you are doing one of the specialized varieties, like the 5:2 or the Warrior diet. There is some flexibility here – for example, some claim that a splash of almond milk is ok in coffee is ok as long as it is less than 50 calories. Other experts maintain, however, that any calories technically break a fast. Like with many of these lifestyle approaches, it can depend on who you ask. 

What you cannot consume 

All experts are pretty much in agreement that zero-calorie sweeteners are off the table unless in a natural form, like Stevia, and even that should be in limited quantities Therefore, no diet soda, sugarless gum, or hard candy is permitted.

Protein powders and any kinds of juice definitely break your fast. That’s why the 5:2 approach is so appealing, because even though you can’t eat much during your fasting days, you can at least eat a little bit throughout the day without having to go into this mind-boggling calculation.  

Black coffee itself will not break a fast, but there has been debate about what goes in coffee and whether that will. Sugar is definitely not advised, but recent research has confirmed that a “bulletproof” coffee formula, infused with either keto creamer, MCT oil or butter, will NOT break a fast. You can read more about the Keto and Bulletproof diets in my article here.

Proponents say

Let me preface this by saying, many proponents are legitimate doctors and health institutions. Even Harvard has endorsed the benefits of IF.  As discussed earlier, Nobel-prize winning research has confirmed IF’s role in promoting autophagy, the body’s renewal process.

There is support in science after studies done on rats showing that they lose weight, their blood pressure, cholesterol, and blood sugars improve. And the benefits of fasting aren’t just about the weight loss, according to the supporters of the approach. Silicon valley executives extol IF for its transformative biohacking effect on their ability to focus and run billion dollar companies. In Forbes Magazine, an article highlighted a study showing that fasting can reset your immune system, lower cholesterol, mitigate arthritis and reduce overall inflammation. The idea behind this is that when we are constantly in a “feed” state, our bodies don’t get a chance to recover and reset. . Some even argue that IF improves and accelerates workout-related recovery.

Opponents say

Of course, with any revolutionary way of thinking, haters gonna hate. The debate around IF can get downright hostile. Jack Dorsey, the CEO of Twitter, caused a lot of controversy when he swore by fasting for 22 hours a day.  Opponents argue that this approach, taken to the extreme,  can become a “dangerous obsession.” They maintain that this type of mindset and incite or reignite eating disorders. It’s even gone as far as publications like the Guardian calling it “anorexia 2.0.” Anyone who has suffered from an eating disorder clearly needs to consider the ramifications of engaging in any time or substance restriction on eating, but it is somewhat convoluted logic to argue that fasting will necessarily lead to a distorted relationship with food. 

Other skeptics point out that there is nothing special about IF for weight loss. According to their argument, any form of slashing calories from diet will yield the same results as time restricted eating. In fact, a study done by the National institute of Health on humans showed that IF yielded about the same weight loss results as what the study calls “CER” or continuous energy restriction  The study itself admits, however that traditional calorie restriction including adjusting macros traditionally does not have long-term success, which is why people turn to alternatives like IF. . 

Level of difficulty – It depends 

I know everyone hates that “lawyer answer” (but I am a lawyer!). It is true, though because there are so many different types of fasting. For me, for example, doing a full 16 hour fast was difficult, but 5:2 was much easier. It also gets easier the more you do it. The rules are more simple on this diet than any of the other ones we have discussed, so if I had to give it a score, I would say it’s a 5 out of 10.


For some of the types of fasting, it is not as extreme as it seems. For example, for 16:8, you can basically leverage your overnight sleeping fast. For 5:2, you have wiggle room to eat a little without being time-bound by the hour of the day. 

There are no bright lines around what you can and cannot eat, and thus no special food prep required. Even though some people accelerate the results with a low-carb diet, that is not mandatory. IF is easier to start during a period where you are working from home since you have more control over your surroundings

Supporters of intermittent fasting also love it because you don’t have to exercise as much. This is pursuant to the logic that the action of fasting accomplishes fat loss and improves insulin sensitivity, similar to the effects of exercise. Still, like a low-carb diet, exercise can be an accelerant to the benefits of intermittent fasting. In addition, exercise while fasting, especially strength training, insures that lean muscle mass is not lost. 


IF can be isolating and inhibit your social life, depending on what kind of IF you are doing. For example, my husband has been doing 16:8 or 18:6 for almost a year now, under his doctor’s supervision. While we enjoy dinners out, brunch is usually not an option. 

Another downside of IF is that the variety of choice is a double-edged sword. There are almost TOO many choices – 16:8 or some other time variation, 24 hour weekly fasts, or 5:2. The best advice I can give is that everyone’s body is different, so you have to do what is right for you. For example, I did not respond to a daily 16:8 approach as well as I did to a biweekly 5:2., 

Also, IF is a conundrum if you like to work out during the day, especially in the morning. Working out without being able to eat afterwards can be difficult. The key is to stick to cardio, especially for fat loss, during your fasting window. If you are planning on lifting that day, save it for your “5” day or for outside your 16:8 window. Studies show that cardio-intense activities like running and cycling, or ones that make heat flush through the body, like hot yoga, actually decrease appetite. Contrary to popular belief, there is no need to eat after most cardio workouts. In fact, pausing on eating after cardio actually helps burn more fat.

It’s a different story for strength training, when  muscles are broken down and depleted of the carbohydrate glycogen. The same is true for HIIT, where you are incorporating intense cardio bursts with plyo moves and breaking down muscles. In both cases, you need to refuel with carbs and protein. So save the HIIT and intense strength training for outside the fasting window, or time to where you can break your fast within two hours. 

IF is not for everyone – as alluded to above, if you have experienced disordered eating in any form, or have blood sugar issues, you should approach any kind of fasting with caution. Both my husband and I have done IF under the supervision of a doctor. I would strongly recommend the same for anyone else that is interested in trying it.

IF products, books and blogs 

There aren’t really many products you can have when you are fasting; but there are some that help along the journey, along with some books I can recommend:


One of the top fasting blogs I would recommend are Jason Fung’s Life in the Fasting Lane blog. For the 5:2 diet, I would also recommend Michael Moseley’s 5:2 diet blog.

The takeaway

The bottom line is, there are argunents to support both sides of intermittent fasting. It’s too inconclusive to term it a “fad” or a miracle solution. You should consult with a medical professional before seriously going down that road. While it has caused a lot of controversy, sometimes we have to do controversial things to change. It is all about what you want and the length that you will go to get it. 


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