What do we mean by Intermittent Fasting (IF) & which type might suit you?

Written by Liz Withyman
November 6, 2023

An Intermittent Fasting routine offers a flexible approach to achieving peak health and the potential for longevity, and not only a longer life-span but also a longer health-span.

IF has many raving fans (including me, and, it turns out, Rishi Sunak!)

It’s an eating pattern that cycles between periods of fasting and eating.

Your fasting window starts after your last meal on one day and extends until you eat again the next or on a subsequent day; and your eating window begins when you ‘break the fast’ (whether that’s at breakfast time or another time of day) and continues until you close the window for the day ie stop eating.

IF focuses on when you eat than what you eat, making it a versatile choice for many people.

So, for example, when Rishi Sunak does his weekly 36-hour fast, he closes his eating window at 5pm on a Sunday and opens it again at 5am on a Tuesday.

Many of the health effects of prolonged 36-hour fasts are seen (albeit to a less intense degree) in frequent, shorter fasts: increased metabolic flexibility; metabolic resilience; DNA repair through autophagy, aka ‘cellular spring cleaning’; production of ketones; cognitive benefits; weight loss; and increased insulin sensitivity.

All of which translates into feeling incredible, mentally and physically, and increasing your chances of longevity.

Types of Intermittent Fasting

There are a number of different types of IF patterns, each with its pros and cons. Some people swear by one approach; others are equally enthusiastic about another. One of the aspects of IF that make it so sustainable is that it is an incredibly flexible way of eating, whereby each individual chooses their own pattern.

Here is an overview of some popular types of IF.

Time Restricted Eating (TRE)

With TRE, you fast for anywhere between 12 and 20 hours each day, which sounds harder than it is, because you’ll be asleep for part of that time. So if you have a 12:12 pattern, that means you would fast from 8pm until 8am the next day, for example.

A very popular TRE pattern is 16:8, where you might eat between the hours of 11am and 7pm or midday and 8pm for example. In other words, delay or skip breakfast, and have a reasonably early evening meal.

If you push your first meal of the day later, or stop eating earlier, or both, you’ll be shrinking your eating window further, increasing the benefits of fasting.

Typically, people who do TRE will have 2 meals each day.

Pros of TRE

  1. Ease: TRE can be a gentle introduction to IF. A 12 hour overnight fast is relatively easy to do. Really, it’s a minimum for good health for virtually anyone, at any age. It’s important that humans stop consuming 2 – 3 hours before bed because our digestive organs get sleepy too!
  2. Metabolic flexibility: your body learns to switch between burning glucose from food for energy and burning ketones / fat from fat stores for energy.
  3. Autophagy: if you fast for 16 – 20 hours per day, your body will likely get the health benefits of metabolic flexibility, ketosis, increased insulin sensitivity and potential weight loss.
  4. Simplicity: a daily pattern of eating within a particular set daily window has the advantage of firm boundaries if you want it to, and no confusion.
  5. Flexibility: conversely, if you want to switch it up, opening and closing your windows at different times, that might work better for some.

Cons of TRE

  1. Reduced benefits: although a 12 hour fast each night is better than not doing IF at all, you would not get as much benefit in terms of potential weight loss, improved insulin sensitivity and autophagy as you would from extended fasting periods.
  2. Too flexible: for people who need strict guidelines, the potential lack of strucure may be a challenge.

One Meal A Day (OMAD)

This is a form of TRE, where you restrict yourself to one meal each day. In other words, it is a 24-hour fast – you just have say, a mid-afternoon lunch each day. This is a pattern I follow regularly.

Your meal can be eaten within a 1 hour period, once a day, perhaps 5-6pm.

Or, some people, like Gin Stephens (author of Feast, Fast, Repeat) spread the components of a meal – starter – main – dessert – over a few hours. They might have their starter at 4pm, and main & dessert at 7pm, for example.

Pros of OMAD

  1. Autophagy: the longer you extend your overnight fast, the more you’ll get the healing magic of autophagy.
  2. Metabolic flexibility: your body learns to switch between burning glucose from food for energy and burning ketones / fat from fat stores for energy.
  3. Insulin sensitivity: likewise, the longer you fast, the more you’ll gain in terms of insulin sensitivity.
  4. Reduced decision making: if you’re only eating once in a day, you won’t have to choose what to eat for the rest of the day…what a time-saver! This goes for all forms of IF, but it’s more pronounced for people doing OMAD than two meal a day fasters.
  5. Reduced cooking time: as above, nor will you have to buy/prepare/cook more than once a day.
  6. Reduced calories/increased weightloss: if you’re only eating one meal, you will probably eat fewer calories while still eating a hearty meal, and this will likely cause you to lose weight.
  7. Flexibility: if you do OMAD in the way Gin Stephens does, eating your one meal in parts over a few hours, you can avoid feeling deprived.

Cons of OMAD

  1. Feeling deprived: I personally don’t do OMAD because I am a foodie and I generally prefer to eat earlier than Gin Stephens, and last out the pleasure to two meals every day!
  2. Adaptation: our bodies adapt to any regular eating pattern, so weight loss might ‘plateau’.

Alternate Day Fasting (ADF)

With ADF, you alternate between fasting days and normal eating days.

On fast days you can either eat nothing at all or do a modified form of ADF which allows you to eat, but severely restrict your calorie intake to for example 500 or 800 calories.

Again, this can look very different for different people. Some prefer to have a little bit of food or very low calorie food throughout the day on a fast day. Personally, if I am doing a short period of ADF to get back on track after a period of feasting – whether that’s Christmas, a holiday or just falling off the IF wagon for a bit! – I find it much easier to do a ‘clean’ fast whereby I only drink water or black tea or coffee all day until about 6pm, when I’ll have a satisfying but low calorie meal such as miso soup with a ton of vegetables, and a chicken breast or similar.

Pros of ADF

  1. Metabolism/weight loss: because of adaptation our bodies get used to any eating routine, which may result in a weight loss ‘plateau’. ADF is a fantastic antidote to that because you keep changing the pattern. It’s such a healing strategy for anyone who has been ‘on a diet’ for much of their lives, and lowered their metabolic rate.
  2. Autophagy: the longer you extend your overnight fast, the more you’ll get the healing magic of autophagy.
  3. Metabolic flexibility: your body learns to switch between burning glucose from food for energy and burning ketones / fat from fat stores for energy.
  4. Insulin sensitivity: likewise, the longer you fast, the more you’ll gain in terms of insulin sensitivity.
  5. Reduced decision making: every other day, you don’t have to make many or any food decisions.
  6. Saving time: you save time buying/preparing/cooking food on the fast days.

Cons of ADF

  1. Hunger / feeling deprived on fast days: it can be tough to know that every other day you’re going to be on reduced rations…arguably not as tough as OMAD (or being on a low calorie diet where every day is like that), but nevertheless, harder than more a flexible TRE pattern.
  2. Temptation on ‘normal’ days: for some people, the temptation is great to overeat rather than eat normally on the non-fast days, which will undermine weight loss efforts.

5:2

5:2 is similar to ADF but you fast (or do a modified fast) for 2 non-consecutive days each week and eat normally for 5 days. So you might choose Mondays and Thursdays as your fast days. Dr Michael Mosley made this form of IF famous in the UK and for many people it’s a sustainable way to fast and lose weight.

Pros of 5:2

  1. Metabolism/weight loss (as with ADF): because of adaptation our bodies get used to any eating routine, which may result in a weight loss ‘plateau’. 5:2 is an antidote to that because you keep changing the pattern.
  2. Metabolic flexibility: your body learns to switch between burning glucose from food for energy and burning ketones / fat from fat stores for energy.
  3. Reduced decision making: on fast days, you don’t have to make many or any food decisions.
  4. Saving time: you save time buying/preparing/cooking food on the fast days.

Cons of 5:2

  1. Reduced health benefits: by eating normally 5 days in every 7, you won’t be getting as many health benefits as if you fasted more regularly, even if you’re losing weight.
  2. Hunger / feeling deprived on fast days: with the other types of fasting, your body becomes accustomed to fasting more regularly, which reduces hunger, whereas this happens less with 5:2 because most of the week you’re eating normally.

Weekly 36-hour fast

This is Rishi Sunak’s approach: he fasts from 5pm on Sundays until 5am on Tuesdays on a weekly basis.

Pros of the weekly 36-hour fast

  1. Intensified autophagy: the longer you extend your fast, the more health effects you’ll get in terms of cellular spring cleaning and therefore DNA repair, and potentially, disease prevention and longevity.
  2. Metabolic flexibility: your body learns to switch between burning glucose from food for energy and burning ketones / fat from fat stores for energy.
  3. Insulin sensitivity: likewise, the longer you fast, the more you’ll gain in terms of insulin sensitivity.
  4. Metabolism/weight loss: because of adaptation our bodies get used to any daily eating routine, which may result in a weight loss ‘plateau’. Like ADF, 36-hour fasting is a good antidote to that because you don’t repeat a daily pattern.

Cons of the weekly 36-hour fast

  1. Hunger / feeling deprived on fast days: as with 5:2, because this is an irregular pattern – only affecting 2 days each week, your body expects food according to your normal daily pattern, so you might experience more hunger than if you had a daily TRE practice for example.

Which one suits your lifestyle?

Would any of these eating patterns fit your lifestyle? If you think it would, but you are looking for some help getting started, or accountability to keep going, or coaching to get you past any limiting beliefs you have about your health, please get in touch.

Liz Withyman

Liz Withyman is an ICF-registered ACC (Associate Certified Coach) who trained with the Coaches Training Institute, the most rigorous and respected coach training in the industry. She runs her online Coached Intermittent Fasting Program 7 Habits for a Vibrant Life several times a year. 

Become Part of
The 7 Habits for a Vibrant Life Community

Join the other women
who are empowering themselves to get energy, clarity and be the weight they want to be by making Intermittent Fasting Easy & Effective

If you want to accelerate your journey to high-energy, vibrant health and live the way humans are evolved to live, join my 7 Habits for a Vibrant Life. You’ll get experiential coaching to work on your mindset, plain-English science in bite-sized chunks and my MicroHabits method to help you implement the healthy habits.

Did you enjoy this?
Here are other articles you may like

For how long should I fast?

For how long should I fast?

For how long should I fast? This is a question I am frequently asked and there is no simple answer, because it depends on your objectives. Different fasts achieve different results Here is a run down of the principle benefits from different fasting periods. Length...

Are you getting enough Zzzzzz for a Vibrant (& long) life?

Are you getting enough Zzzzzz for a Vibrant (& long) life?

In this blog I’m taking a look at some science around Habit # 4 of my Coached Intermittent Fasting program: SLEEP!  That most pleasant and fundamental bedrock of a Vibrant Life, which is hugely undervalued and under-prioritised in our society.  Not getting enough...

Fasting Fuel: Fantastic Fish pate with lime

Fasting Fuel: Fantastic Fish pate with lime

Principles behind my Fasting fuel series The food you choose for your eating window can either help or hinder your fasting practice. Choosing high fibre, high protein, high healthy fat foods made of real ingredients will support you to maintain the habit, because...

Fasting Fuel: Quick Bean Fettuccine with Tahini Salad

Fasting Fuel: Quick Bean Fettuccine with Tahini Salad

Principles behind my Fasting Fuel series The food you choose for your eating window can either help or hinder your fasting practice. Choosing high fibre, high protein, high healthy fat foods made of real ingredients will support you to maintain the habit, because...

Join the Discussion

0 Comments

Submit a Comment

Your email address will not be published. Required fields are marked *