What is Alternate Day Fasting?

If two days fasting and five days of normal eating seems too indulgent or too slow for weight loss you could try fasting every other day.

Alternate Day Fasting  (ADF) is the most scientifically studied of the intermittent fasting methods.  ADF was first used in studies of fasting in animals (rats and mice) and, more recently in humans.  ADF was studied in animals as part of research into how calorie restriction  (85% of their normal calories) extends the life of animals, such as fish, worms and rodents.1  The researchers noted that when rats were put on restricted rations (which were given to them once a day), they ate all their ration within an hour and so were, in effect, fasting for the remaining 23 hours of the day. The researchers wondered whether it was the fasting or the reduced calories that were causing the animals to live longer, so they tried giving the animals  unrestricted food on one day followed by a fasting day of no food. They found that these animals, like those on the restricted calorie intake, also lived longer.  Not only that, but the animals were less likely to develop diabetes, had lower blood pressure and heart rate, less cancer, better nerve health, and lower rates of kidney disease. This prompted further research into how fasting might work to cause these benefits, and eventually studies of ADF in humans were started.1  We are still a long way off from knowing whether ADF or any form of intermittent fasting will  result in a longer life for us humans, but we already know that it can help with weight loss and, as the main risk factor for so many diseases is being overweight, that alone is a good reason to including fasting in our way of life.

Learn more about the science of fasting

Although ADF has been being studied for many years, it has only recently started to be used as a weight-loss tool.

Learn more about alternate day fasting: The Every Other Day diet 

 

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Inventing your own fasting method

Flexible fasting: invent your own intermittent fasting method

If none of the fasting methods described in the previous pages appeal to you, why not invent your own? After all, intermittent fasting just means abstaining from food for a while –  to allow your body to start using up your fat stores and to get on with some repair work. You can easily create your own method following these general principles.

Time between meals

It takes about 5 hours for you to digest a meal (depending on the size of the meal) and a further 5 hours before your body really enters the fasting state when all the great changes to your biochemistry take place. To get the best out of fasting, therefore, you need to have at least one 12 hour period with no calorie intake. Extending the fast to 16 or 20 hours is even more beneficial.

Learn more about the science of fasting

Fast/feast

Intermittent fasting is not just about the time you go without food, but also about how you eat when you are not fasting. If you calorie restrict yourself every day you’ve turned it into a standard ‘just eat less’ diet and you will feel deprived and be far more likely to stop doing it. Further, when we eat well we reassure our bodies that we are not in a famine situation and this helps to prevent various changes happening in our bodies that put pressure on us to over-eat. So, ensure you alternate your fasting times with periods when you can eat normally. Remember, you are relying on the feasting times to get all the nutrients you need, so while you can eat what you want, be mindful of what choice you are making!

Learn more about what and when to eat

How many times a week?

In your enthusiasm to maximize the benefits of fasting, make sure you don’t do too much. Use this general guide to how often to fast:

  • if you’re fasting 5–7 times per week keep the fasts less than 16–18 hours.

  • if you’re fasting 3–4 times per week fasts can be up to 20 hours long

  • if you’re fasting 1–2 times per week  fasts can be up to 24 hours long

  • if you’re fasting once a week it can be up to 60 hours long.

There will be times when fasting is not a good idea. Learn more about fasting and stress.

Self-experimentation

Experiment with different ways of fasting to see which one suits your current lifestyle and give you the results you want. But don’t be afraid to change it whenever your life changes. This is what makes intermittent fasting such a great way of eating – you make your diet fit your life not make your life fit the diet!

Whatever fasting method you follow, you can use these principles to adapt things anytime that life gets in the way of your normal schedule.

Why I like to mix my fasting methods

Forum member rawkaren says “I work with all fasting methods depending upon what is going on in my life and how I feel. 16:8 keeps me in check especially when I’m travelling and hard to monitor intake, 5:2 for when I don’t need to think too hard about weight loss and 4:3 or ADF when I’m in the mood for going a bit faster. Mixing it up keeps it fresh too.”

Read why other forum members chose their fasting method

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Fasting two days a week: The Fast Diet or 5:2 diet

The most popular form of intermittent fasting is to fast on two days each week. You simply pick two days that are convenient to you and on those two days you have no or very few calories. The other 5 days of the week you can eat well so you don’t feel constantly deprived like you do on low calorie diets. The flexibility of being able to choose the days that suit you means your social life will not suffer, and yet you will lose weight!

The two ‘fast days’ are not even a complete fast. Most people choose to have a low calorie meal or two on their fast days, so they never need to go to bed hungry. How you organize these meals on your fast days will depend on how your body responds to fasting. Some like to have a small breakfast and a medium evening meal; some like to  eat only an evening meal or only lunch. Others prefer not to eat anything but to take their calories in liquid form, such as soup. If you are trying to lose weight, it’s best to limit your calories on your fast day to around a quarter of your normal needs (which would be 500 calories for an average woman, and 600 calories for the average man).

Learn more about two days a week fasting:

 

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Different ways of intermittent fasting

There are many different ways of doing intermittent fasting. Let us introduce you to the most popular ones, so that you can decide which would be best for you.

Your choice of fasting method may be influenced by your personality, your lifestyle, or your goals.  One of the great things about fasting is that you can experiment –  you can always change your approach, or mix and match to create your own method.

There are four main methods of Intermittent fasting. Learn more about each of them:

If you’re not sure which fasting method to try, read on!

Tips to help you decide on the best method for you

Until you try a fast, you don’t know how your body will react, so pick a method and just do it! The type of fasting that’s right for you may change over time but you have to start somewhere.

  • If you want to ease gradually into fasting and you’re happy to skip breakfast, you could start with a daily ‘eating window’ approach such as the 8-Hour Diet (16:8) and, if necessary, increase the fasting time as required. You can then either keep up with daily fasting or change to two or three days of longer fasts.  Learn more about fasting every day 

  • If you want to combine fasting with muscle building try daily fasting with Leangains or the Warrior Diet. Learn more about fasting every day 

Although intermittent fasting is very flexible and can be changed around to suit you, it’s a good idea to try to keep to the method you’ve chosen for a month or more to see how it affects you. It takes time to adapt to fasting and while some people will show immediate weight loss, for others it can take several weeks. Be patient and allow your body time to adjust to your new way of eating.

Read why our FastDay forum members picked their fasting method

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Fasting 3 days a week (4:3) and other variations

If fasting two days a week seems too little but fasting  on alternate days sounds too much, you could try splitting the difference and fasting 3 days a week.  This gives the advantage of being able to have the weekends free to indulge (if you want) and being able to  have the same fast days each week, making planning  your life much easier.

Many people in the FastDay community have adopted this method, generally fasting on Mondays, Wednesdays and Fridays. As with 5:2 and ADF, you eat around 500 calories on fast days (600 calories for men) and eat normally on the non-fast days.

Is this the intermittent fasting method for you? Jump to Getting started: your first fasts

Why I like 4:3

Forum member MaryAnn says: “I chose 4:3 in particular because I wanted to drop some weight quickly before a 10k race. My intention was to switch to 5:2 afterwards, but I liked the rhythm of 4:3, and found it easier to have fewer non-fast days in a row.”

Read why other forum members chose their fasting method

Johnson Up Day Down Day (JUDDD)

The Johnson Up Day Down Day (JUDDD) is probably the first ADF diet to be used for weight loss. The creator of the JUDDD, Dr James Johnson, has published several scientific papers on the benefits of ADF.1  It is slightly more structured than the Every Other Day diet  as it starts with an induction phase for two weeks, during which you eat only 500 calories on the down days, but after this you can choose to eat more on the down days if you want slower weight loss or to maintain your weight. Another major difference from the Every Other Day diet is that a diet supplement, termed resveratrol, which is a substance found in small quantities in red wine, is promoted as a means of enhancing the effectiveness of the diet in terms of the health benefits.  However, when all the studies on resveratrol were critically reviewed by scientists,2 they found that the evidence for benefit was fairly poor and questioned the marketing of the supplement. Further studies are clearly needed to determine whether it is worth spending money on such a supplement.

Learn more about the science of fasting

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Who should not do intermittent fasting?

Fasting isn't safe for everybody

Should I fast? Is fasting safe for me?

The vast majority of people find fasting – whether they follow the 5:2 diet or another form of intermittent fasting – is a great way to improve their health and lose weight, but of course there are some for whom fasting is not recommended. For example, because fasting affects hormones that control growth, children, teenagers and pregnant or breast-feeding women or people recovering from surgery should not fast.

In particular, intermittent fasting is not recommended for:

  • Children and teenagers who are still growing

  • Women who are pregnant

  • Women who are breast-feeding

  • People who are recovering from surgery

  • People with eating disorders

  • People with diabetes controlled by insulin

  • People who are underweight.

If you are taking certain medications or have certain medical conditions, you should check with your doctor first:

  • If you are taking warfarin

  • If you have any condition that results in a weakened immune system

  • If you are taking prescription medicines that must be taken with food.

Also, there are times when you should consider pausing your fasting schedule:

  • When you are unwell or have fever

  • If you are highly stressed

If in doubt, consult your doctor.

Learn more about when to take a break from fasting

 

Fasting for too long

Fasting is one of the most powerful things you can do to improve your health. However, there are ways of fasting that are not so healthy. Any fast that involves no or minimal calories for 5 days or more risks causing ‘refeeding syndrome.’ Refeeding syndrome usually occurs within four days of resuming eating. Refeeding syndrome cause nerve, lung, heart and muscle problems and can even be fatal if not recognized and treated early. For this reason FastDay does not endorse fasting for more than 36 hours with no calories or 3 days consecutively with very low calories.

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What is intermittent fasting?

Come and join us!

Intermittent fasting (IF) is simply taking a break from food for at least 12 hours and no more than 36 hours – on one or more days each week. In fact, you’ve been fasting every day of your life but you didn’t realise – as we all fast overnight. Our bodies are well adapted to managing without food, not just during the night but for much longer.

Learn more about the science of what happens to our bodies when we fast

What is the 5:2 diet (also known as The Fast Diet)?

The 5:2 diet is just one pattern of intermittent fasting: you fast for two days each week and eat normally on the other 5 days. Many people who follow 5:2 have been inspired by The Fast Diet, a best-selling (and very good) book by Dr Michael Mosley and Mimi Spencer. But there are many ways of doing intermittent fasting. Some of the most popular include:

  • The 5:2 diet (The Fast Diet, Eat. Stop. Eat. and The Two-Day Diet)

  • Alternate Day Fasting (The Every Other Day Diet)

  • The Eating Window approach (Leangains, 16:8 and the 8 hour diet, Fast-5 and The Warrior Diet)

Learn more about 5:2 and other ways of doing intermittent fasting

What are the benefits of intermittent fasting?

Most people start out with intermittent fasting in order to lose weight, but there are many other benefits. You will reduce your chances of developing many of the diseases associated with modern life, including heart disease, stroke, and diabetes; you’ll gain control of your eating habits (such as emotional eating and bingeing), and learn to listen to your body’s food needs. You will no longer be afraid of hunger or be dominated by food. It’s really liberating!

Learn more about the health benefits of fasting

How easy is fasting?

Fasting is surprisingly easy. Hunger pangs come but then they go again. A drink of water, a walk, keeping busy – any or all of these will help you overcome a hunger pang. Fasting does require a little bit of willpower, but if you’ve ever dieted before and had to deny yourself food for days on end, you have definitely got enough will power! With intermittent fasting, your willpower only needs to last for a day at most. Yes, you will feel hungry now and then, but it won’t do you any harm.

Learn more about how to start fasting

Fasting is a Way of Eating for life

Fasting can be used as part of a diet if you are aiming to lose weight. It works.

But the real beauty of intermittent fasting is that it can become a permanent and sustainable part of your life. You can adopt a new and better Way of Eating forever!

Long term intermittent fasters can expect health benefits…but are also free from the yo-yo cycle of dieting, losing weight, then putting it on again.

Fasting gives you a tool that you can use in lots of different ways so that it suits your own lifestyle and circumstances.

Fasting is so easy and so flexible; you will be in control.

The FastDay community now includes thousands of people who have adopted this Way of Eating for life, Come and join us!

Learn more about fasting for weight maintenance

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Intermittent fasting for weight loss and weight control

You lose weight steadily. And it is sustainable forever.

Fasting is a great way to lose weight!

It works steadily – perhaps not as rapidly as other diets – but by learning how to do intermittent fasting your weight losses will be sustainable and permanent.

Fasting is not like other diets; it does not take over your life. You do not need to spend all your time counting calories, and you can eat the food you love on non-fast days. It’s not even really a diet, it’s a new Way of Eating.

Unlike other diets, fasting is easy, flexible and sustainable.

How quickly will I lose weight on the 5:2 diet or other fasting patterns?

Based on scientific research (unlike most diets), intermittent fasting in various forms has proved an effective way of losing weight. Depending on your choice of fasting method, you can expect to lose around 0.5kg (1lb) per week. Some weeks you might lose more, others less, but over time down it will go.

How does fasting for weight loss work?

There are five reasons that intermittent fasting is so effective for sustainable weight loss:

1. When you’re fasting you are reducing your calorie intake. Even though you eat normally the rest of the time, your total calorie intake will fall – so you will lose weight. This is obvious, of course!

But there is actually more to it than that.

2. Surprisingly, the periods of fasting do not make you more hungry, instead your appetite on non-fast days is decreased, so you end up eating less on those days as well.

3. The time spent fasting teaches you to understand the difference between real hunger and eating due to boredom, emotion, or just because it’s time to eat, so you’ll find that you’ll snack less – even on non-fast days.

4. Because you can still eat your favourite foods when you’re not fasting you won’t feel that sense of deprivation that comes with diets where many foods are forbidden. This makes the fasting Way of Eating much easier to sustain.

5. Fasting is more effective than simply eating fewer calories 7 days a week, because when you are fasting your body burns fat to a much greater extent than previously. Compared with other diets, intermittent fasting shrinks more fat with less muscle loss.

Learn more about the science of fasting

Keeping slim by fasting

Once you have reached your target weight, your fasting method can be adjusted to keep you at your target. Many people move from 5:2 to 6:1, for example. What’s more with your new skills, you’ll be able to enjoy meals out, vacations and celebrations without worrying about whether you’ll gain any weight; just increase your fasting for a short time and any gains will quickly disappear!

Learn more about fasting for weight maintenance

The FastDay community

Many members of the FastDay forum have been fasting for well over a year. A visit to our free forum will give you the chance to connect with thousands of other successful fasters and see for yourself how much easier it is to lose weight by fasting than by all those old fashioned ‘eat less, move more’ diets.

What’s more, you can easily continue with fasting to keep the weight off and to maintain the health benefits.

Fasting success stories

The FastDay forum has a host of inspirational stories from people who had struggled for years with their weight but through fasting found they could not only reach a healthy weight but maintain their weight loss: something they had never been able to do before. Here are some of their stories:

Sue.Q’s story:

“This time last year I gave all my “smaller”  clothing away to charity shops, given up on the weightloss game and was feeling very low indeed, had a really bad hip/back problem resulting in physio,  I wasn’t housebound but very nearly because of my foot and leg swelling problem which early in the new year got to a “severe” state being only able to wear men’s fully adjustable sandals because nothing else would be anywhere near fitting and my life was horrendous physically mentally and painfully 😯

I sent for the book and thought I can do 2 days each week on 500 calories, got started right away without any planning whatsoever.

I found it very easy to do so immediately did 3 days each week, resulting 4:3 which I didn’t even know existed at that point, then a couple of weeks later I found this forum, learning far more from everyone’s experiences.

I will never look back on any of those decisions at all,  plus I actually do enjoy my fastdays.

After 8 months I’ve lost 50 lbs, bought a complete new wardrobe of “interim” clothing, dropped down a group on my BMI, dropped 3 sizes in my new clothes. The icing + cherry on the cake is the VAST change in my legs and feet I’m now wearing all my (women’s!) sandals, shoes and boots that were still tucked away in the spare room.

I really can’t put into words the difference this has made to my life, and as usual when I re-live this memory like now I’ve tears in my eyes.   I’ve always said on this forum that this way of eating has truly saved my life and it has because there’s only one person who knows (me) exactly the stage I’d got to and the point I was close to.”

Nora’s story

“I catch sight of myself in a shop window:  Instead of seeing a plump lady, looking away quickly and sucking my tummy in, I am amazed, jubilant, happy and sneak another look.  Here’s how:

Last summer, I saw the BBC Horizon program and the health benefits were an immediate attraction as I have a very close relative who is insulin dependent, and the idea of only counting calories on 2 days a week made it seem easy enough.  I started with the intention of going for the long haul.

Very soon, I found I was not overly hungry on fast days and was definitely enjoying the sense of discipline and of being back in control.  At first, I nibbled the evening before a Fast Day and thought about food constantly but this eased off fairly quickly and I began to lose the habit of snacking on non-fast days, too.  I shared my calories between 12 noon lunch and 7pm dinner and, as I have always struggled to enjoy breakfast on a daily basis, I started to miss this meal out every day. (I posted a comment and Dr M emailed me back to say the necessity for breakfast is a myth and he is doing more research.  Excellent support.)

In March, I reached my target weight and although I still had a bit of plumpness around my middle, I planned to move onto 6:1 and see how my body redistributed things.  But before I could establish a routine, I found that even without any fast days, I was still losing a little weight every week and my other stats were also reducing.  So the 7 hour eating window obviously does it for me.  Others have posted similar benefits.

Back from holiday and of course I had put a few pounds on (oh, the pasta, the ice-cream) but a return to the 7 hour eating window meant that after 2 weeks, I was back down to the weight I was before I went away.  And I have a complete new wardrobe of clothes from the back of the wardrobe that now fit again, for free.

Today is my 65th birthday. I weigh 127 lbs, have a 29 inch waist, a 27.3% fat ratio, a 20.2% BMI. I feel good and am hoping if not for more years, to be healthier, fitter and more able to enjoy the years I have left.”

natsw’s story

“I have had a battle with my weight from my teens onwards. In truth, looking back, I didn’t really have a problem in my teens but I felt I did and that made it all the easier to let the pounds pile on thereafter. I have tried so many diets I can’t remember them all. Ten years ago, in my early thirties, I lost a lot of weight after following a “Zone” type diet but developed hair-loss and stones in my gallbladder which resulted in its removal. From then on I decided that diets and me were finished. Twenty years of misery was enough. I felt I was living proof that diets didn’t really work long-term and after the traumas of gallbladder attacks, then the operation (followed by another trip to A&E), I just wanted to be well.

So that was it. I did stop dieting. And after a while I stopped worrying about my weight. I wouldn’t say I was happy about my weight but I decided that as I feminist I wasn’t going to be defined by my clothing size. The fact I had a partner who always loved me and found me attractive didn’t hurt. I started to realise how boring people were when they were dieting – women beating themselves up and talking about being “bad” – I felt very happy not to be part of their number any more. Then I started reading about the 5:2 Diet. What really appealed to me were the health benefits. Losing weight was not my reason for starting: I just wanted to be healthier. I didn’t tell friends about it, I just got on with it.

One year on and I couldn’t be happier that I decided to give 5:2 a go. I undoubtedly feel healthier, less short of breath, less tired but I have also lost 3 stone. It may not have been my motivation for starting but it was certainly a welcome side-effect! It hasn’t all been smooth going. I’ve regularly had weeks (sometimes 3 or 4) where I didn’t lose a thing, or even put on a pound or two, but through it all I’ve stuck with it and slowly the weight has come off. I’ve never been tempted to fast more than two days a week and on non-fast days I eat completely normally, including eating cakes and biscuits if I want them. For me that has been the key. How could I even think of giving up when five days a week I eat whatever I want? Of course my appetite has changed – I don’t want to eat the portions I used to – but I don’t feel like I’m on a diet.

The single biggest thing that has changed is my attitude to food. I don’t obsess about it and I don’t get into a panic about not having access to food all the time and that goes for fast days as well as non-fast days. On every other diet I have ever done I become fixated on food: what can I eat when? How many calories is this thing? If I eat that now what will that mean for later. On fast days it’s completely different. What I can eat is so limited I just plan it in advance and don’t worry about it on the day.

I’ve spoken to lots of people who have given up 5:2 because the weight loss is too slow. But now one year on they are all still struggling to stick to diets and I am 3 stone lighter. I don’t mean to sound smug but this is the first time in my life that I’ve really felt that this is a way-of-life rather than a diet. I don’t find myself calculating how many pounds I will have lost by a certain date and I don’t long for it all to be over so I don’t feel in denial. I hope I don’t sound too melodramatic when I say that I think 5:2 has changed my life. I know that my weight-loss will likely slow down (it already has) but I will stick with it and continue to reap the other benefits while hoping that, however slowly, the weight will continue to come off. The main thing is that it just feels like a massive relief and that is probably what I like best about 5:2.”

TedE’s story

“After 1 year of 4:3:

– 39.8kg, 87.8lb, 6 stone 3.8lb gone (or as a friend of mine put it, I’ve lost a 12 year old);

– BMI down by 12.28 (49.07 to 36.79 or 25%);

– My day to day clothes are even more comically loose. I threw out some big items, but still haven’t wholesale replaced my wardrobe, just wearing some older stuff along with some of my biggest stuff (in this regard, my belt is my best friend);

– Clothes that fit well in 2001 (when I was finishing High School) are now slightly too big.

The second lot of 6 months has been characterised by long periods of plateau followed by sudden large losses (including around 4 kgs in one week). Funnily enough the plateaus seem to occur as I’m approaching and around a milestone (ie 130kgs & 120kgs, 30kgs lost & 40kgs lost) though I have no idea why, presume this is coincidence. I understand plateau is fairly common around the 6-9 month mark of any dietary intervention so not terribly concerned, just a bit frustrating. Just hoping the next 6 months are a lot faster.

I feel great. Even though I’m still quite big, I feel quite light on my feet and energetic. I also feel a lot stronger and like I have more endurance.

Fasting is now so easy I usually don’t eat at all on fast days and sometimes don’t break the fast at breakfast the next day, carrying on until lunch time if I don’t feel hungry.”

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Intermittent fasting for health

I don't see hunger as a problem to be solved anymore. I eat better even when I am not fasting. Getting into new and better habits! We love it!

Health benefits of fasting

When you fast, powerful changes take place in your body.  These changes can have significant health benefits, potentially reducing your risk of diabetes, heart disease, cancer or Alzheimer’s.

Learn more about the evidence, and the science of fasting

The health benefits of fasting are not completely understood, and a huge amount of research remains to be done (we at FastDay want to be part of this), BUT there is encouraging evidence that fasting may decrease your risk of:

  • Diabetes: scientific studies in animal and humans have been able to show fasting can reduce insulin resistance (the main cause of type 2 diabetes)
  • Heart disease and stroke: insulin resistance is also well established to increase the risk of heart disease and stroke and lowering insulin resistance has been shown to reduce heart disease risk
  • Alzheimer’s disease: studies in animal models of Alzheimer’s disease have shown that fasting can delay the onset of the disease
  • Scientific studies of the effects of fasting on other conditions in animals and in humans are underway.

At FastDay we are constantly monitoring the scientific research into fasting and it is our mission to keep you updated with all the latest developments.

Are you a research scientist working in the field of intermittent fasting? We would love to talk to you and learn more about your work. Please contact FastDay.

Learn more about the health benefits of fasting

What if you already have type 2 diabetes or other medical conditions?

Few scientific studies have yet been done but short-term fasts have been proved to help blood glucose control in people with diabetes. Several people in the FastDay community who have type 2 diabetes have found that fasting has helped them improve their blood sugar readings, reduced their need for diabetes drugs and given them control over their condition.

While no scientific studies have been performed in people who have heart disease, there have been scientific studies showing that fasting improves risk factors for heart disease in obese men and women.

Learn more about fasting with diabetes and other medical conditions

 

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