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The ultimate guide to intermittent fasting

Lose weight, improve your brain health and live a long and healthy life.

Intermittent fasting. Does the hype reflect reality?

You’ve probably heard about intermittent fasting but you’re unsure what it is and if it’s as good as what people say.

You may even be wondering if intermittent fasting is dangerous.

I’m here to tell you, when done properly it’s one of the best ways to maintain good health.

It gives you more energy, reduces body fat, helps with brain function, fights off diseases and increases your chances of living a long and healthy life.

I have been intermittent fasting for the last 18 months and the positive effects it has made on my body and sense of well-being means I will do it for the rest of my life. It isn’t a fad.

The list of benefits of intermittent fasting continues to grow as science makes new discoveries. Put these benefits into pill form and you will become a billionaire overnight.

There is a general lack of understanding when it comes to intermittent fasting so first-things-first:

  • Breakfast is NOT the most important meal of the day
  • Going without food will NOT cause your body to cannibalise itself

If you’re new to intermittent fasting or have done it before but looking for further information this guide is for you.

I’m hopeful it will give you all the information you need to make a decision on whether intermittent fasting is for you.

The most important meal of the day is not breakfast

Neither is it lunch or dinner. Let’s get this out the way first.

Eating breakfast (which means ‘breaking fast’) can hinder your health more than help it.

Let’s get some common myths out the way:

  • Skipping a meal won’t make your body hold on to fat
  • Fasting doesn’t cause your body to shut down
  • Eating frequently won’t speed up your metabolism
  • If you go too long without food your body will start eating itself (muscle)

There is no scientific evidence to suggest fasting does any of the above yet people continue to believe them.

What is intermittent fasting?

Before we get going it’s useful to give a clear definition of what intermittent fasting is.

Humans have fasted for hundreds of thousands of years and through evolution your body is designed for it. It’s only in recent times we have started eating at regular times and intervals.

In today’s society, we are lead to believe that we must eat regularly and at least every four hours. This is incorrect.

Growing up you were told that you should eat every morning because “breakfast is the most important meal of the day”. Again, this is incorrect.

Starting the day with a nutritious breakfast, you were told, helps set the tone and gives us much needed energy for the day ahead.

For years the media would peddle this myth to sell us cereals and other breakfast foods. But that’s all it was, a myth.

This myth didn’t come from any scientific studies but by marketers working for the companies that sell the sugar-coated cereals you see on supermarket shelves. In other words, of course, cereal companies will tell you breakfast is the most important meal of the day.

So, what is intermittent fasting?

Let’s start with what it is not.

  • It is not a diet plan
  • Though weight loss is likely to occur it is not a quick way to lose weight

The Wikipedia definition of intermittent fasting says it’s, “an umbrella term for various diets that cycle between a period of fasting and non-fasting.”

Wikipedia is slightly off here because intermittent fasting is not a diet. A more accurate definition is;

Intermittent fasting is an umbrella term for the various protocols that cycle between a period of fasting and non-fasting. 

It can be done in conjunction with a specific diet but intermittent fasting does not require you to eat specific foods.

Intermittent fasting is a protocol or set of protocols which differ depending on the one they’re following.

The history of intermittent fasting

Humans have been fasting for hundreds of thousands of years.

Hunter-gatherers sometimes fasted because they had no choice. If food was scarce or, even worse, a famine occurred then they had no option but to fast.

Their nutritional intake had less sugar and flavour-rich foods than a typical Western diet so they craved less.

Fasting was part of a coming-of-age ritual among some tribes and was often carried out before a tribe went to war with another tribe.

Religions too have a history of fasting. Islam, Judaism and Christianity all have (or had) fasting play a key role as a part of their faith.

plato fasting
Plato knew

The Telegraph has an excellent article on the history of fasting. It covers how fasting was a part of our early ancestors’ lives because they did not have access to food. It has been used as a sign of protest (think Gandhi) and continues to be part of religion to this day.

Fasting of some kind has been around as long as humans have. It’s a natural way to live.

Intermittent fasting and longevity go hand-in-hand

To reap all the benefits above through fasting is more nuanced than you might think. The key to optimisation is through time spent fasting.

There’s no fasting time ‘sweet spot’ on how long you should fast, but doing it for a minimum of 16 hours will provide you with some of the benefits.

Fasting for 24 hours will show even greater results and likewise fasting for 48 hours occasionally even more so.

Have you ever tried asking someone to go without food for 24 hours? They’ll likely assume they will die of starvation.

I’m being sarcastic of course and in reality going without food, or spending less of the day eating it, is actually better for you.

Watch this interview with Dr Rhonda Patrick and Dr Valter Longo on the effects intermittent fasting has on longevity.

The benefits of intermittent fasting

This is where it gets interesting.

This is where the magic happens.

Intermittent fasting has a myriad of health benefits.

It’s one of the best lifestyle choices you can do for your health and I include it alongside exercising, sleeping well and reducing chronic stress. The effects of it are so profound that trying it could change your life.

Now, I realise I’ve hyped it up a lot here, so here’s a caveat.

There are different protocols of intermittent fasting covered further in this article. Some protocols require you to fast longer than others. It often depends on what your goals are and indeed which suits your lifestyle.

The benefits listed here are from all protocols of intermittent fasting. In other words, you may not receive all these benefits if you do only one type.

For example, listed below it details how it can regenerate the entire immune system. This is a phenomenal benefit of intermittent fasting but don’t expect it to happen if your fasting window is 18 hours. It requires more time in the fasting state for it to take effect.

Make sense?

benefits of intermittent fasting

Benefit #1. It supports with hormone regulation and lowers diabetes II risk

Insulin is the hormone behind diabetes I and diabetes II. It’s released from the pancreas when you eat, raising your blood sugar levels. But by fasting your insulin levels normalise thus providing long-term diabetes II risk.

Human Growth Hormone (HGH) also increases due to fasting. Low HGH has an association with higher levels of body fat and lower levels of muscle mass. By increasing HGH you can decrease body fat and increase muscle mass.

Benefit #2. It helps with calorie restriction

Calorie restriction is proven to help you live a longer life. It’s a ‘hack’ used by people in the longevity and life extension community as a means of prolonging their life.

Intermittent fasting shortens the time you can spend eating which makes it easier to restrict the calories you eat. Calorie restriction is not the goal of intermittent fasting but it makes it easy if you want to.

Once you get into the swing of intermittent fasting your body stops craving breakfast and even lunch. The more you do intermittent fasting the more your body stops being hungry because usually we’re hungry through habit not necessity.

Benefit #3. It helps you lose weight and body fat

The lower insulin and increase of HGH breaks down fatty tissue in the body, particularly in the stomach area.

This means that elusive area that men including myself often find the most difficult to shift body fat is less of a problem. The process happens because fasting shifts your energy metabolism into fat-burning mode.

From my own personal experience, I can vouch that it does indeed help with shedding body fat. Shifting fat from the stomach area has always been my difficult spot but fasting makes it much easier.

In fact, intermittent fasting can help you lose body fat regardless of where it is.

Benefit #4. It reduces inflammation

Inflammation is the body’s attempt to protect itself from harmful stimuli like damaged cells and irritants. It’s a protective immune system response which is necessary but it also causes damage and thus ageing.

One study found that alternate day intermittent fasting can reduce markers of inflammation in overweight adults. Another also found that inflammation reduced in a metabolic function marker through fasting.

If you’re not convinced by those two, this study found it reduces inflammation in the brain. For more on brain health, see benefit #6.

Benefit #5. It helps your cells clean and repair themselves

Cell damage is a part of ageing. You can’t stop it (not yet, anyway) but you can slow the process.

Research has found intermittent fasting promotes cell self-cleaning. This is called autophagy and it’s where the cells clean up, repair and get rid of any waste. It’s one of the best ways to promote longevity.

One study found that short-term intermittent fasting helps with autophagy in the brain. Another study found that mitochondrial activity increased while participants were fasting.

Benefit #6. It helps the brain create new neurons and protects against brain damage

Neuroscientist, Mark Mattson, found that reducing energy intake has all kinds of positive effects on the brain.

How do you reduce energy intake? Fasting and calorie restriction, of course.

Once again you can thank evolution for this.

Our hunter/gatherer ancestors would not have survived unless the brain was functioning at a high level when they were hungry. In other words, when they were hungry and looking for food the brain had to be working at its best or they would die out.

Intermittent fasting increases the production of proteins in the brain called neurotrophic factors. It also increases the number of mitochondria in the nerve cells. Maintaining brain health is important for a long life.

Watch Dr Mattson’s excellent TEDx talk on the topic.

Benefit #7. It regenerates the immune system

Fasting for three days can regenerate the immune system according to research from the University of California. It found that after three days of no food dormant cells began to renew themselves. It also killed off older and damaged cells during the process.

“The study has major implications for healthier aging, in which immune system decline contributes to increased susceptibility to disease as people age.”

As I get older I plan on fasting for three days periodically to regenerate my immune system. You should too. It could add years to your life.

Intermittent fasting programs

When it comes to intermittent fasting programs you have a wide choice of options. Some of the most popular ones I’ve listed below.

Choosing a program depends on what your goals are and what kind of lifestyle you lead.

Intermittent fasting is easy for some as health and fitness is their life. They can do any protocol with ease.

Most people, however, work long hours and have busy lives. They try to lead a healthy lifestyle but sometimes it’s not manageable. If this is the case for you, you’re best going for a more simplistic method of intermittent fasting.

Below is a guide on some of the intermittent fasting programs available. Thanks to Alex Nguyen’s paper which provided guidance on some of these programs.

36/12 fast

In this program, you eat every other day and on your feeding day you give yourself a 12-hour window to eat.

On your feeding day, you may start eating at 8am on Monday and finish at 8pm that same day. From 8pm onwards you won’t eat until 8am the following Wednesday giving yourself a 36 hour fast.

The 36/12 fast was made popular by Dr James Johnson and his book, The Alternate-Day Diet (Amazon).

The 5:2 fast

The 5:2 program was popularised by Michael Mosley and advocates fasting for two days a week and eating normally for five.

An example week on the 5:2 fast might look like the following. On Monday and Thursday you no more than 500 calories and on the other days you eat as normal.

The 5:2 Diet was created on the back of a BBC documentary on the benefits of fasting and has gone on to be a popular book (Amazon).

Eat Stop Eat

Eat Stop Eat is a 24 hour fast developed by Brad Pilon and is probably the easiest fast to follow.

You don’t eat for 24 hours for one day a week. And that’s it.

Pick one day of the week you won’t eat on and do it. It’s easy for beginners or for people who don’t want to restrict their eating all week.


The Leangains fast was created by Martin Berkhan for weightlifters and bodybuilders.

Sometimes called the 16/8 diet, this approach consists of a 16 hour fast with an 8 hour eating window each day. Berkhan advises that the 8 hour eating window should be at the same time every day.

This program was made with athletes in mind so it recommends a diet high in protein, carb cycling and fasted training.

Warrior Diet

Like Lean Gains, the Warrior Diet is a 20 hour fast with a 4 hour eating window. The Warrior Diet is flexible allowing you to eat small amounts of food during the fast.

Created by Ori Hofmekler, The Warrior Diet is intended to mimic the eating habits of Spartan and ancient Greek warriors.

Filling your daily calorie intake during the 4 hour eating window may prove difficult. It also recommends eating toward the end of the day which might make sleeping with a full stomach uncomfortable.

The 382 day fast

In 1965 a man in Scotland fasted for 382 days going from 207kg down to 82kg. The then obese Angus Barbieri from Tayport, Scotland, lived on a diet of tea, coffee, water and sparkling water.

382 day fast
Image via ScoopWhoop

Granted, Barbieri was severely obese but it proves that the body can survive if it can feed off its fat.

What can I consume while fasting?

You have to avoid consuming calories or your body is not in a fasting state. A small amount of calories is OK but any more and you are defeating the object of fasting.

Some people drink just water during a fast but you can have other drinks like coffee, tea and sparkling water. Consuming these certainly worked for Angus above.

There are lots of health benefits of coffee but if you’re drinking either it or tea, don’t drink milk or at least go easy on it. Adding a lick of milk is fine but any more than that and you may technically break your fast. I add a few drops of milk to my coffee when I’m fasting.

Other than coffee, I drink water. I drink a lot of water too because it helps with feeling full and, well, water is good for you too.

drinks to consume when fasting

Best types of intermittent fasting for women

Intermittent fasting should be done with caution at any time and with anyone. That said, women are more susceptible to hormone imbalances while fasting.

This is because women’s bodies are more sensitive to signs of starvation, so taking extra care is a must.

Some signs of hormone imbalances include;

  • Fatigue
  • Low mood
  • Bloating
  • Headaches
  • Irregular periods

The excellent Dr Axe blog recommends that women new to intermittent fasting should try ‘crescendo fasting’ first.

Crescendo intermittent fasting means fasting on non-consecutive days. The basic premise is this;

  • Fast on two to three nonconsecutive days.
  • On fasting days do yoga, strength, or light cardio.
  • Ideally, fast for twelve to sixteen hours.
  • Eat normally on your high-cardio days
  • Strongly consider taking 5-8 grams of BCAAs during your fast.
  • Drink plenty of water. Tea and coffee are okay, too.

Best type of intermittent fasting for men

There are no specific types of intermittent fasting that are suitable for a man’s body. If you’re reading this as a man it all depends on what your goals are. Looking to lose fat? Ensure to restrict your calorie intake. Want to hold on to strength and muscle? Try the Leangains program.

Men aren’t as sensitive to hormone imbalances as much as women. That’s not to say they aren’t sensitive at all, however.

Fasting may cause a man’s testosterone to drop if he is not careful and doesn’t prepare well enough. Be on the watch out for mood changes and lack of energy.

My own experience with intermittent fasting

I have been intermittent fasting on and off for 18 months and it is one of the best health protocols I’ve introduced to my life.

I was a sceptic initially and the first few days of intermittent fasting wasn’t a particularly pleasant experience. This was my body getting to used to the process and after the initial bumpy period I began to feel much better. Great, in fact.

My intermittent fasting protocol looks something like this:

  • 17/18hr fast
  • Stop eating at 8pm (the time of my last meal)
  • Start eating at 1 or 2pm the following day
  • I allow myself water and coffee (black or sometimes with only a splash of milk) during the fast
  • Three times per week

I generally eat two square meals during the feeding window and, unless I’m being meticulous about what I eat, I may have a treat like a bag of crisps in between.

I usually don’t count macros unless on a rare occasion I’m being meticulous and I don’t beat myself up if I occasionally eat a lot of junk. I try to apply the 80/20 principle to intermittent fasting. Get 80% of it right and don’t worry about the 20% you don’t.

This seems to work well for me even when I’m training hard and consistently. The benefits I’ve received doing this method were:

  • I lost body fat quickly
  • My sense of wellbeing heightened
  • My focus when working has increased
  • My skin looks healthier to the point where people have commented on it. Intermittent fasting is now part of my male skin care routine
  • Helped with calorie restriction as I was consuming around 2,000 – 2,300 calories per day
  • I stopped craving food and learnt to differentiate when I was genuinely hungry and when I wanted to eat through habit
  • My resting heart rate dropped from 57 to 49bpm within a week

#intermittentfasting update. Resting heart rate has dropped from 57bpm to 49bpm within a week.

— Stephen Davies (@stedavies) July 2, 2016

Some negative effects were:

  • I lost strength in the gym. Though I looked more ripped and the strength came back as soon as I ate more
  • After 20 days of consistent intermittent fasting I developed a flu-like I have never had before. I have no evidence to suggest this was anything to do with the fasting however

I plan on introducing a 24 hour and 36 hour fast into my regime. The longer the fast the more you should prepare the body by building up to it.

Not eating for 36 hours when you’ve had no experience of fasting in the past will likely make you feel terrible.

How to start intermittent fasting

Like most healthy changes you have to make incremental changes to your eating habits. No one is expecting you to suddenly stop eating for a longer period than normal and be fine.

It would be the same as asking you to run 10 miles at a brisk pace if you’ve never run in years. Or asking you to bench press your bodyweight if you’ve never lifted a barbell before.

It’s a gradual process but what is probably harder is society’s views on going without food for a sustained period of time.

You’ll get strange looks from people when you tell them you’re intermittent fasting. The belief that you should eat three square meals a day is so ingrained that it will take years for the facts to get through to the mainstream.

The best thing to do when you start intermittent fasting is to take it slow. As a general guide:

Week 1. Fast two days a week for 16 hours.

Week 2. Fast three days a week for 16 hours.

Week 3. Fast two days a week for 18 hours.

Week 4. Fast three days a week for 18 hours.

While doing this during your first month, try to get a sense of how your body is feeling.

Notice your mood and how your focus on work and life in general. Make notes if it helps.

Intermittent fasting is integral to your health and longevity

There are simply too many benefits for it not to be.

If you live in a seasonal climate it should be easier to fast during the spring and summer time as the body doesn’t crave food as much during the winter months.

Living where I live I find it more difficult to fast during winter time as I feel more hungry during this time. The summer months are a breeze.

If you’ve never tried intermittent fasting before then it’s certainly worth having a go. Be patient and don’t judge the effects based on a day or two.

It takes time for the body to adapt to, what you might call, its natural way of eating.

For me, intermittent fasting will be a part of my life for as long as I live. Hopefully, by doing it I’ll live longer too.

The supporting evidence is too conclusive and I know first-hand how it makes me feel.

If you care about maximising your health for as long as possible and want to feel (and look) better then intermittent fasting should be a part of your life too.

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