Alternate Day Fasting: What Makes It Different, And How to Effectively Follow It

Fasting in of itself is simply a period of time in which you restrict yourself from eating and/or are restricted from eating

The time between your last meal and the first meal of the next day for example; hence why we call our first meal “breakfast” – we’re breaking a fast.

There are many iterations of fasting, from fasting windows in a day, to whole day fasts to even multi-day fasts. Some even have cultural and religious drivers (Ramadan for example).

Alternate day fasting (ADF) is one such iteration of the fasting approach to dietary and calorie intake. A 2019 study defined ADF as "strict 36-h[our] period without caloric intake ('fast days') followed by 12-h[our] intervals with ad libitum food consumption ('feast days')."

Essentially, you fast for 36 hours and have a 12-hour eating window; fairly straightforward.

There are however more variations of the ADF approach. Full day, or 24-hour fasts are quite popular, however, arguably the most popular approach among dieters is the ​5:2 fasting diet, pioneered by Dr Michael Mosley, a British journalist. This blew up in popularity when it was highlighted on a number of media channels, including the BBC, for its health promoting benefits.

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This form of alternate day fasting has been described as “modified” fasting and, instead of complete abstinence from food intake, instead calorie intake is severely restricted (to less than 800kcals a day provided via nutritionally complete diet shakes).

Exciting new lines of research have implicated ADF in assisting with weight loss, improving metabolic markers of diabetes, lowering the risk of heart disease and even having an “anti-aging” effect!

How Does Alternate Day Fasting Differ from Intermittent Fasting?

The difference between both approaches is fairly straightforward; ADF involves fasting for entire days at a time whereas intermittent fasting (IF) refers to a restricted eating window applied every single day. You can find out more about intermittent fasting itself in our other in-depth article on the subject.

So, instead of the 36-hour fasting window seen in the ADF approach you would have an eating window of 4 – 8 hours during a given day.

The Benefits of Both Approaches

Both alternative day fasting and intermittent fasting offer similar health boosting benefits. These approaches to dieting have been followed for thousands of years and, as we mentioned, the practices may be founded in cultural / religious origins.

As society has become increasingly unhealthy and overweight, new approaches to address the issue have been trialled and fasting may be the key to long term success in maintaining healthiness and a healthy lifestyle for many people.

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In fact, it has been shown that fasting is just as effective as a daily calorie-controlled diet for weight loss / management, offering an alternative for those who struggle with consistent calorie restriction over long periods of time.

Fasting itself isn’t just limited to helping manage body weight. Here are some other of the evidence backed benefits of fasting that you may not have realized;

How to Decide the Best Fasting Plan for You

This will all come down to personal preference at the end of the day and weighing up the practicality, sustainability and the cohesiveness of the approach towards you achieving your given goals.

Many will take a “black and white” approach to which form of fasting you should practice whereas, in reality, the best approach may be to trial them all and see which works best for you (if at all).

Starting with IF may be a more viable approach for most as they get used to the feeling and schedule of a fasting regiment. Whole day fasts may be quite intimidating for first time fasters (as mentioned), but simply restricting the window in which you can eat may be a better way to “dip your toe in” to the practice of fasting instead of “jumping in at the deep end”.

If you find the restricted windows simple to incorporate into your daily schedule (or to adjust to) then aim to progress to ADF, if even just to trial it for a period of time to see how it suits you.

Read Also: How To Overcome Keto Weight Loss Plateau

A gradual progression to the more intensive form of fasting, in this case ADF, would be advisable. It’d also allow you the time to develop a structure and plan (relating to your exercise, diet, supplementation and sleep) that’ll ensure you’re not contending with worries like nutrient deficiencies, hunger related sleep disruption, fatigue, reduced exercise recovery etc. and instead allow you to reap the absolute optimal results possible from following a fasting diet.

How to Follow an Alternate Day Fasting Meal Plan

Following a fasting and caloric restriction plan can be daunting at first and the prospect of not eating for x amount of hours may seem a little overwhelming. Some may experience adverse reactions, such as overeating on non-fasting days, irritability and fatigue and so preparation and understanding of what is to come is key when planning your first extended fast.

First things first; let’s forget about food directly for a moment and consider other health and lifestyle behaviours which can impact our calorie intake.

sleeping peacfully at night

Arguably the primary lifestyle factor you should consider correcting before anything else is to look at your sleep pattern, especially if you are not already achieving seven to eight hours of high-quality sleep a night consistently. 

Missing out on important sleep time can impact upon your blood sugar regulation and insulin sensitivity, impacting your sense of fatigue, cravings, mood etc.

Next would be exercise; you may want to plan when you break your fast around exercise. While exercise has been shown to stave off hunger short term, it can also lead to an increased sense of hunger later on (when the appetite supressing effect has dissipated). 

So, using it as a tool on your completely fasting day may lead to some late-night food related sanity issues, whereas it may be useful to fit it in early just prior to breaking your fast on your non-fasting days.

A general rule of thumb would be to simply perform very low-intensity exercise on your completely fasting day, so as to mitigate any elevations in hunger (as well as not requiring a great deal of recovery which more intense exercise demands).

exercising with jump rope
Stress

The last major lifestyle factor to highlight is stress management. Stress plays a key role in hunger regulation, with elevated levels of stress leading to reductions in satiety and a tendency to desire and crave hyperpalatable foods (typically rich in fat and sugar).

Effective stress management has been shown to minimize these cravings and improve satiety levels.

Ok, ok, back to food.

Now, while food intake itself may be restricted, there may be non-calorific beverage options that you can incorporate into your daily routine that’ll help combat hunger.

fluids to go with fasting and exercise


Fluids are a great tool for minimizing hunger as they can fill up our gastric tract which in turn signals the release of hunger quenching hormones. The more the gastric tract is filled, the greater this cascade of hormones released into our system telling our brain that we’re full.

Read Also: Best 5 Electrolytes For A Keto Diet

A few great options to add in;

  • Green (or other herbal) tea
  • Black coffee (either regular or decaf)
  • Zero sugar / kcal energy / carbonated drinks
  • Sparkling water
  • Diluting juice and water
Male fitness athlete

The caffeinated beverages are a great addition as caffeine is a recognized (and fairly potent) appetite suppressant. It can also help increase the breakdown of existing fat stores for energy while preserving lean body mass! And if that’s not enough, if you do choose to exercise on your fasting days it can even help to maintain, if not improve, your exercise performance while fasted!

Non-calorie diet drinks may also be an effective tool for managing cravings and appetite.

If you’re choosing to start with an ADF approach which doesn’t restrict intake of all foods but imposes a severe calorie restriction (to that sub 800kcals a day we see in popular modalities like the 5:2 approach) then the use of nutritionally dense shakes may help.

Whey protein powder may be your best friend on these days; include a scoop of whey, a few heaped handfuls of green leafy veg, a portion of mixed berries and a low kcal milk alternative (such as coconut or almond milk) and this will land you a shake in around 200kcals packed to the brim with essential vitamins and minerals, fiber and protein (a perfect calorie friendly health elixir for your fasting days).

In conclusion

While the majority will see fasting simply as a means of losing weight, we have to emphasize that it is not just a weight loss diet; it’s a way of eating, and living, and should be considered as such.

We noted off all the potential health benefits of fasting that extend far beyond weight loss, so to look at it as simply a way to help you shed those last few pounds would be a disservice to the approach itself.

To be successful at following the fasting diet approach it’s all about planning and understanding structure; identify how you can make the approach best fit your life and it’s demands and gradually incorporate the approach as opposed to dive head first into it (as this can be the downfall for many first time fasters who undermine the critical thinking which goes into following the approach successfully).

The age-old adage of “fail to prepare, prepare to fail” couldn’t fit any other dieting approach better. However, the rewards for successfully incorporating fasting into your lifestyle may be well worth the added effort.

Jamie Wright

Jamie Wright

Jamie is a registered nutritionist and REPs recognized personal trainer with a MSc in Nutrition and BSc in Sports and Exercise Science. He runs his own nutrition and exercise coaching company, OUTWRK, and has authored a number of books of which include HealthyHer and FitHer. He has contributed on a number of external organisations nutritional guidance educational notes/booklets aimed at recreational exercisers/dieters to elite, internationally competing athletes. Additionally, Jamie has worked with this spectrum of clients in the past and just released his new program Everyday Athletes aimed at recreational exercisers/dieters. Reach out to him on his website for nutrition advise or consulting.

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