5:2 Calorie Restriction v. Fasting for Newbies

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5:2 Calorie Restriction v. Fasting for Newbies

This topic contains 73 replies, has 30 voices, and was last updated by  mkpnut 6 years ago.

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  • Hi:

    I am seeing much more confusion between doing 5:2 and ‘fasting’. Another way to put it is confusion between severe calorie restriction and the length of time between eating. For the record, it is the severe calorie restriction twice a week that leads to weight loss when following 5:2 (and, perhaps, other ‘health benefits’), not the time between eating.

    5:2 was born from a documentary Dr. M did on calorie restriction and life extension (not weight loss). Only one of the four basic segments of the show was on fasting. That segment was all about a four day fast that yielded good blood work results (‘fast’ meaning eating no food for four days) . However, the researcher involved said that to continue benefiting, you would have to do four day fasts monthly (I’m going from memory), and Dr. M decided that he could not do fasts that often even if he did get the positive results.

    Another segment was on a man that had been eating 1900 calories a day for over 10 years. He weighed 134 pounds and was in excellent health. Dr. M decided he could not do that, either. A third segment was on ADF – alternate day fasting – where people alternated between eating 500/600 calories one day and eating what they wanted the next. That approach yielded good blood work and weight loss results regardless of what people ate on their non diet days. The fourth was on calorie restriction and Alzheimer’s. Initial research on animals indicates severe calorie restriction can delay its onset

    At the end of the show, in consultation with the researchers, Dr. M came up with what we now know as 5:2 and decided to try it for five weeks. It worked for him, yielding good blood work results. The show noted as an aside that Dr. M lost weight. After it was aired, people tried 5:2 (presumably for the potential health benefits) and began losing weight. Recognizing a good thing when it appeared, Dr. M quickly wrote a weight loss diet book (not a life extension diet book), and the rest is history.

    The point is 5:2 is about calorie restriction, not fasting in the sense of time between meals. To explain, I see people not eating (fasting) for 24 hours (say, 2 pm to 2 pm the next day) and thinking they will automatically lose weight. But they eat their TDEE before 2 pm (because they will not be eating for a ‘day’) and eat their TDEE after 2 pm the following day (because they are hungry), often with 500/600 calories in between. There is no calorie restriction, they do not lose weight, and they quit because ‘it does not work’. It is the same for 16:8, don’t eat until 5 pm or any other ‘time between eating’ diet plan. They can work, but only if you count your calories and make sure you eat under your TDEE every day. They are reduced calorie diets, that do not have the potential health benefits that come from severe calorie restriction, using an IF (‘Intermittent Fasting’) label. I have nothing against any weight loss diet ‘that works for you’, but this is the 5:2 site, so I am focusing here on how ‘the real 5:2’ works (not options or off-shoots).

    So if you are a newbie here because you want to try 5:2, I recommend you start by doing 5:2 correctly for at least two months before you start thinking of doing something else.

    ‘Doing 5:2 correctly’ means going to bed, getting up, eating 500/600 calories while you are awake, going to bed, getting up and eating normally – twice a week. ‘Normally’ means eating your TDEE or less. Here is what you need to know about TDEE: http://thefastdiet.co.uk/forums/topic/tdee-for-the-curious-or-why-dont-i-lose-weight-faster/. And here are some general tips for those just starting: http://thefastdiet.co.uk/forums/topic/warnings-to-newbies/.

    There are tens of thousands of people quietly being successful with 5:2. The ones who are not being successful generally are simply eating too much on their non-diet days (and often their diet days, too). It makes no difference if you eat a (small) breakfast, lunch and/or dinner on your diet days, eat only one meal or don’t eat anything, because time between meals is irrelevant. It is the severe calorie restriction twice a week that counts!

    Good Luck!


    Thanks that all makes sense. I started a week ago and have my last meal at around 6.30pm on a normal day and the following (fast) day I eat 1 meal for 600 calories and nothing else that day. Next day I eat normally, so I hope I’m doing it okay 🙂


    You are doing 5:2.

    The next challenge may be your pattern of weight loss. This might help: http://thefastdiet.co.uk/forums/topic/really-no-weight-loss/

    Good Luck!

    Thanks 🙂

    I’ve started 5:2 today, Had 580 Calories then will eat as normal tomorrow. Going to calorie count on my normal days to 1500 calories.

    Is this ok?

    Hi Katy:

    Just going from your name, you should try to get to 500 on your diet days. That does not mean you ‘failed’ by eating 580. The neat thing about 5:2 is it is a way of eating, not a diet that you either do or don’t. But since the twice a week severe calorie restriction is the key to success under 5:2, the 500 is sort of a real goal. Quite a few interesting, unexpected but very beneficial things seem to come from the severe calorie restriction that do not show up when following normal, reduced calorie diets (which 5:2 turns into if you don’t have two severe calorie restricted days a week).

    Normally you can eat up to your TDEE on your non diet days if you want to, but there is no reason why you can’t eat less.

    The basic (and scientific) rule is the less you eat, the more you lose.

    Good Luck!

    I haven’t read the book but previous posters have mentioned that it discusses the advantages of leaving as much time as possible between eating to allow the body to go into ‘repair mode’. (The time quoted I can’t remember exactly but it was a matter of hours, not four days) If people are doing this for health/disease prevention reasons then surely this is really important. Can anyone clarify because I am currently working out my strategy for maintenance and this could make a big difference to how I do it. I am thinking of either 2 days doing 1/2 calories or 1 day doing 1/4 calories. If the period of ‘fasting’ is irrelevant then I can be much more flexible, but it’s really important for me to maximise my chances of avoiding health problems later in life.

    It’s an interesting question and you are not the only one asking himself. I have not found any research comparing the different eating patterns, however, there appear to be health benefits to other forms of intermittent fasting like 16:8. With 16:8 there is no restriction of calories during the feeding window, yet people report improved wellbeing. Again, I do not know if there is research into this particular type of fasting.

    For my part I do not eat on my fasting day until teatime, I only have two mugs of coffee with milk in the morning. My thinking is that I want to reduce insulin levels and break the insulin resistance that is behind my type II diabetes. If I eat every few hours, in particular food containing carbs, my body will excrete insulin every time and I have no idea what overall effect this small rise in insulin levels has. As a result of this purely theoretical musing I try to keep the longest possible fasting period.

    This is my second time on the fast diet. About a year ago I began and just could not stick with it. On the fast days I found trying to limit calories to be too difficult and was never really satisfied.

    I am now actively involved in my second round and fast on Mondays and Thursdays. On my fast days I don’t eat any food at all. Just some tea, a cup or two of coffee (just a bit of cream – one tablespoon), and lots of water. I prefer the total fast to trying to limit calories to 600. I do not to eat after 8:00 in the evening on any feed day. So my two fast periods are about 36 hours each. Each fast day has gotten easier and I have little difficulty in not eating. While I do get tired and might get a mild headache for a while in the afternoon it soon passes. Exercise really works to curb my appetite on fast days. I’m nine weeks in and have lost about 15 pounds. I’ve also noticed that on most feed days I’m not as hungry as I used to be and don’t eat as much.

    Drron, I do the same thing, water fasting that is. Whenever I have tried a different version of fasting, I have always failed and ended up eating more than I should. I don’t want to have anything to do with food on fast days, and that’s it:)

    Simcoleuv, thank you ever so much for always reminding us that at the end of the day it’s all down to calories restriction. However, I would think that, given that one doesn’t go over his TDEE and follows the 5:2 plan correctly, fasting for some hours on non fast days would help with weight loss, in the sense that the body burns whatever there is to burn and then resorts to burning fat. Does this make any sense?

    Hi Nina:

    Conceptually, calories are a zero sum game. If you don’t eat for a long enough period of time (and this varies by individual), you will burn fat to keep going. But then you eat, and if you have calories you don’t need at the time, they go to fat and you are where you would have been anyway.

    Having stated the theory, recent research (that needs to be confirmed) indicates that the fewer times you eat a day, the better the weight loss and blood work results, at least for people with type 2 diabetes. One group ate six times a day, another two times a day. The nutritional and caloric intake of the two diets was identical. After three months, the two groups switched diets and went for another three months. The results were that the two meal a day group(s) lost more weight and had better blood work results than the six meal a day group(s). http://www.diabetologia-journal.org/files/Kahleova.pdf. There is much interesting there, including the fact the groups ate identical diets but the two meal a day groups lost materially more weight.

    Here is an interesting quotation from the study:

    “Our results are in strong agreement with animal studies,
    which have demonstrated the glucose-lowering effects of
    intermittent fasting regimens (such as every other day fasting
    or fasting for 2 days a week). These regimens reduce blood
    glucose and insulin concentrations, improve glucose tolerance
    [4, 28], mainly due to increased insulin sensitivity [29], and
    extend the lifespan of laboratory animals [30].

    Our data contradict the widely held opinion that eating
    more frequently is healthier than eating less frequent larger

    This would seem to suggest that there is some benefit to somewhat extended times between meals on a daily basis (as suggested by concepts like 16:8 – or just skipping some meals). This area of research is rapidly expanding, and I suspect we will be hearing much more on the subject over the next few years.

    simcoeluv, I’ve mentioned that a few times: a calorie is NOT a calorie, even though this is being repeated like a mantra. Human beings are NOT closed systems and the first law of thermodynamics cannot be applied to a body that gives off heat easily or gets sunburned (both should not happen if we were closed systems).

    Most people, even those that are not (yet) diabetics, have a leaning towards insulin resistance; it is most likely an evolutionary hangover. Because of this and the fact that most foods apart from fat raise insulin levels (glucose and proteins) or increase insulin resistance (fructose), our bodies deal with different “calories” in different ways.
    Studies of overfeeding have shown that human bodies do not gain as much weight as expected if they are fed a low carb high fat diet. They simply increase base metabolic rate by thermogenesis (literally, turning the heat up) but do not store much excessive fat.
    On the opposite side, simply reducing daily caloric intake by “eating less and moving more”, as we are constantly told, leads to reduction of BMR that can persist for months after caloric restriction has ceased.

    There are people that do not respond in those ways and they do well whatever they eat and whichever way they decide to lose weight. For the majority of us a calorie is NOT a calorie. Otherwise our first ever diet would have been a lasting success, we would have eaten less, lost the weight and kept if off indefinitely.

    Hi Dummerchen:

    There is some evidence that some foods take more calories to burn than others, and that the body treats carbs differently than fat and protein. For instance, we now recognize that carbs are digested and converted to blood sugar quite quickly, and if they are not immediately used via physical exertion, are deposited as fat. Unfortunately, this leaves the person hungry and they eat even more. The obesity epidemic, as it is called, looks like it may be caused by the low fat, high carb diet.

    I am not familiar with any studies showing excess caloric intake not leading to weight gain because of the food being eaten. If you have any links to such studies, I would be interested. As far as I know, the current studies on foods causing metabolic increases are pretty much stymied because the amount of increase, if any, simply can’t be measured with today’s technology.

    However, I am familiar with studies on high fat/protein diets. One in particular (that I participated in) required people to eat 20 grams or less of carbs, daily, for several months. But the participants could eat as much fat and protein as they wanted. The participants lost weight like crazy, (some two or more pounds a week), even though they could eat all the non carb containing foods they wanted (no alcohol, though). The people kept detailed, daily food diaries.

    The food diaries were kept to keep track of carb intake, but when they were analyzed for caloric content, the results were shocking. It turned out that even though the people could eat as much fat, meat, eggs and cheese as they wanted, and because of that were never hungry, their daily caloric intake was around 1200 calories a day. They lost weight because they were not consuming very many calories, not because the foods they were eating caused a metabolic increase.

    The non scientific way to explain why eating fat and protein can cause weight loss and eating carbs may not is to think of a fast acting pill versus a timed release pill. Carbs are fast acting (as most athletes that carbo load before their activity know). Carbs create blood sugar quickly and provide quick energy. When that blood sugar is not used quickly, however, it is also quickly deposited as fat. The result is low blood sugar and hunger (sugar high, low sugar crash).

    Fat and protein are digested by the body much more slowly (leading some to suspect it takes more energy to digest them). They provide a much lower and much more constant supply of blood sugar to the body. As a result, eating fat and protein satisfies hunger for longer periods of time and people eat less because they are not hungry.

    Many people on 5:2 soon recognize this in regards to their diet days. They often decide that the food they eat on their diet days should be high protein/higher fat because they find they are less hungry when they eat those kinds of foods. Many people are also surprised that they are not starving when they wake up after their diet day. By that time, most are feeding off their own fat and do not need to have their blood sugar supplemented by eating food.

    Sorry for the non-scientific science lesson, but it is quite an interesting topic that most people on any diet can benefit from.

    Thank you for taking the time to write such a long and well-thought-out response. I agree with what you said, based on my own experience.

    Hi all, its really interesting reading everyones take on this. I got interested with 5:2 after seeing the BBC doco last year. I had never dieted but found at 46, I was weighing in at 96kg at 181cm in height. I also had high blood sugar like Dr M. I started in December 2013 on the diet. I quickly did more research and found via this website, Brad Pilons Eat Stop Eat. He really explains the science of fasting and the benefits. The weight loss for me was important but the side effects of the insulin regulation and autophagy to name just a couple is a real positive for me. I have lost 10kg, 10cm off the waist and a cm from my neck to date. I adopted Brads regime where he does actually fast on his fast day. So I would eat dinner on a Sunday at 7pm, then eat absolutely nothing until 7pm Monday, only drinking water. I repeat this on a Thursday. I like the idea of trying to really kick the body into an autophagy mode by not eating at all. On my non fast days I try to eat well – mainly vegetables, fruit, meat and fish and limiting my sugar intake. Other side effects for me are I have found I sleep so much better (especially at the end of a fast day) and have also found some nerve issues in my leg to have really settled down (I am an above knee amputee from an accident). I have read that fasting may help with neurological issues. My aim is to lose more weight and then adopt either a one day a week fast and/or a leangains style which I have experimented with a bit where on non fast days I will not eat until midday – a 16 hour fast then an 8 hour eating window. As i am an amputee i cant run or walk long distances so use a concept rowing machine for fitness. I do a HIT program on that as well as longer low intensity sessions. All in all I am a huge fan of IF. I got my brother onto it and he has also lost 8kg and is now at his ideal weight. I think the bottom line is everyone has a different way of tackling IF but for me, I enjoy the complete 24 hour fasts and the benefits they have brought. Best wishes to all.

    Started 5:2 4 weeks ago. I have seen reduction from 72 to 67.6 (4.4 kg in 4 weeks)

    42 yr old male
    BMI – reduced from 24.9 to 23.3 Target BMI – 20 (60 kg)
    BMR – 1543 kcal
    TDEE – 2000 kcal (between sedentary and lightly active)

    Sometimes I think I have exceeded 600 kcal on fast day – by 50-100 kcal but does not seem to have impacted the weight loss. I am not monitoring other health benefits.

    I do consume less than my TDEE in fact I struggle to consume just about my BMR on feed days. That’s the impact of 5:2. I just can’t seem to eat more even if I try. My body tells me when it is done.

    #anyway long journey and I’ll only believe this works if I can lose another 4 kg over next 6-8 weeks. But so far so good. not much impact on waist line yet but hoping soon to see that in a few weeks.

    Hi takloo:

    Congratulations on your progress!

    The numbers you have given would indicate that if you were eating to your TDEE (and I know you said you were not) you could expect to lose about 3/4 of a pound a week. The fact you have lost over two pounds a week is probably a combination of eating less on your non diet days and water weight loss.

    I’m responding because you say you will only believe 5:2 works if you lose about a pound a week (or more) over the next 6 to 8 weeks. I certainly hope you do, and that is certainly possible, but don’t be surprised if you hit a ‘plateau’. If you do I recommend you not quit, because you have already proven you can lose weight following 5:2. Sorry to say, 5:2 comes with no promises of how fast or how consistently any given individual will lose the weight.

    Good Luck!

    thanks simcoeluv.

    Is water loss bad or that’s part of the journey.

    I did 4:3 for 2 weeks. That may also have caused more weight loss than 5:2.

    I am still not seeing any difference in my paunch. I hope to lose weight from that region next. No one has said to me that I have lost weight.

    Though weighing machine shows 4.4 kg weight loss. I’ll continue this way of life for 2 months at least and see where it goes from there.

    Hi takloo:

    Water loss is not bad or good. Your body has different water needs over time an retains or expels water to match those needs. Many people on starting a diet lose quite a bit initially, and hope that rate of loss continues. They become disappointed when it does not. The fact is it is hard to lose a lot of fat weight rapidly. To lose two pounds of fat weight a week consistently, a person has to cut 1000 calories a day from their diet. That would mean you would have to average eating 1000 calories a day to lose two pounds a week, given your TDEE of 2000.

    A second way to do it is for a person to increase their exercise substantially. However, that carries two challenges. First, it takes a lot of exercise to equal a pound of fat loss a week (I have to run over 18 miles to burn a pound of fat), and second, if you start exercising a lot more than you have been your body retains water to help repair and strengthen the muscles you are using. The water retention masks the fat loss and it looks like you are not making progress. Both lead to unhappiness when people fail to lose weight as quickly and as much as they feel they should, given their hard work of both being on a diet and exercising a lot more than they used to.

    When it comes to weight loss, life just isn’t fair.

    thanks today is fast day for me…again going for 4:3 this week….I am getting addicted to “not eating”…it is so easy “not to eat” than I would have thought 4 weeks ago

    once I get to 64 kg (BMI 22) I would be relaxed about it …never been above 25 (max 25.5 BMI) but not been that low in 10 years…..

    ultimate goal is 60 kg (BMI 20)…I wonder how would I look if and when i reach there…still a long way to go

    at 0.5 kg / week it would take 2 months to reach 64 and 4 months to reach 60 provided i dont heat the proverbial plateau and stick with the regime

    question – does not eating BMR / TDEE calories on feed days affect weight loss adversely


    ‘question – does not eating BMR / TDEE calories on feed days affect weight loss adversely’

    There is no research that indicates that eating fewer calories will lead to slower weight loss. The fastest way to lose is to eat nothing (not recommended). You seem to be proving that eating less is causing more weight loss.

    I’m not sure why you want to weigh 132 pounds, but Good Luck!

    It is one of those things…psychologically then I would have great margin of error and even if I increase the weight by a few kilos from that point would not be an issue and would be easier to bring under control

    also I want to try to reduce the paunch which I think will begin below 65kg. another 3 kg to go.

    Interesting today I weighed with not much clothes on and found it was actually 350 gms reduced – may be coincidence.

    when considering weight for BMI, BMR, TDEE do people consider net weight or weight with clothes on


    Clothes off.

    ‘You seem to be proving that eating less is causing more weight loss.’

    well I’ll continue to monitor and post…as I said if this continues for next 2 months then indeed calories restriction is the way to go

    Started 5:2 4 weeks ago. I have seen reduction from 72 kg to 67.6 kg (4.4 kg in 5 weeks)

    after 10 days no weight loss – though the weight fluctuated from 68.7 to 67.3. So there was increase to 68.7 and then down to 66.3 and now back to where I was 10 days back.

    how to confirm if I am losing water / fat weight and not muscle weight.

    fasting is so easy….hope the weight loss resumes though…not sure yet how to lose the paunch…there is certainly some improvement but not near where I would like

    Started 5:2 6 weeks ago. I have seen reduction from 72 kg to 67 kg (5 kg in 6 weeks)

    I had a medical check up last week and apart from confirming the weight reduction it also stated that the BP, blood sugar etc are fine. Cholesterol is slightly higher but reduced compared to the test 6 years ago.

    Started 5:2 (more like 4:3) 7 weeks ago (gosh time moves fast). I have seen reduction from 72 kg to 66.5 kg (5.5 kg in 7 weeks)

    I have feasted on non-fast days occasionally but that does not seem to have hindered the weight loss. Also on fast days I have sometimes gone above 600 kCal but even that does not seem to have affected the weight loss and health benefits.

    So I dont think the rules are hard and fast. You can take some liberty both on fast and non-fast days based on my limited experience.

    Hello you seem to have experience re the 5:2 . Can I just ask if my last meal was at 8:30 pm last night do I have to wait 24 hrs before my next meal , as I thought I read that the 500 cal meal could be around 2pm today. Or is this a mistake and I should have waited till 8:30pm tonight . Also if eating didn’t work out well today can I scrap today and make tomorrow my fast day? Not sure if I am following it correctly yet . Sorry to be pain thank you for your help


    No pain, common questions.

    ‘Doing 5:2 correctly’ means going to bed, getting up, eating 500/600 calories while you are awake, going to bed, getting up and eating normally – twice a week. ‘Normally’ means eating your TDEE or less.

    That means you can eat your 500 calories anytime from when you wake up to when you go to bed. There is no requirement that you wait 24 hours (or any other time period) between meals. Many people eat just one high fat/protein meal in the evening on their diet days because they find if they eat earlier they get hungry before bed. The high fat/protein is most healthy and satisfies their hunger until they wake the next morning.

    Also, any two days a week work, so if you miss one day, make it up another.

    Good Luck!

    I am going to bed after my normal meal. Getting up and no food only water and tea for the full day. Drinking/eating a “cup of soup” around 6pm.Going to bed, getting up and eating normally. Doing this Monday and Thursday each week. Is this ok?

    Hi Evelyn and welcome:

    Perfectly fine.

    Good Luck!

    I have been doing 5.2 for about 18 mos. (Started Apr/2013) My motivation was not to lose weight. It was for blood pressure, cholesterol, glucose benefits. Base as tested before 5.2 was 160lbs, 138/98, total LDL/HDL; 235 (good HDL/HDL balance) Glucose: 161 After 4 months on the 5.2 145/150lbs BP: 109/90 Cholesterol: 194 Glucose: 91
    My weight dropped within the first month to 145 during the 2 days and 150 during the 5 days. I do the 2 days consecutively on Starting Tuesday at midnite and don’t start eating normal until Thursday noon so I am on 2 day mode for about 60 hours. Some friends/family tried the 5.2 but have a tough time doing the 5-600cal. and get too hungry. I really don’t have a problem. If I get the nibbles, I have a glass of water and maybe some carrot or half a tomato/apple but stay within the 600 cal. area. Do a 1 hour yoga class 3 times a week. I am so happy with the results that I see myself staying on the 5.2 for my lifetime.

    Dr. Krista Varady’s recent research seems to address the question of when you should eat on your diet days. Here is her summarization of her research on the topic:

    “Quick update: Our “meal timing” study is now finished and the results have been published in the Journal, Obesity. Please find a link to the abstract below…
    Results from this study show that people can eat the fast day meal at dinner or as small meals throughout the day and lose the same amount of weight as eating the meal at lunch. This is contrary to what we expected…before the study was complete, we assumed that people would not be able to control their calories if they ate small meals throughout the day. We were wrong!
    In short, feel free to spread your fast day calories throughout the day if this works for you.”

    If I drink a Green drink made from barley and wheat grass on my fast days, does this ‘break’ my fast? I’d like to drink this in the mornings as a way to nourish with liquid and to assist my body to returning to an alkaline state.

    Hi JYHG:

    You are mixing apples and oranges. 5:2 is a weight loss diet. As long as you ingest 5/600 or fewer calories on your two diet days each week, you will be following the 5:2 diet. It depends on the calorie content in your juice whether or not drinking it will reduce the effectiveness of 5:2.

    Aside from weight loss, if you are concerned about getting into the ‘fat burning’ mode for ‘other health benefits’, then ingesting carbohydrate calories ‘breaks’ the fast, so your juice will stop any progress you might make toward that goal.

    Good Luck!

    Great thread simcoeluv.

    There is certainly much confusion over 5:2 and you put it well in your initial post.

    I have for two years thought of 5:2 (or in my case 4:3) of eating 1/4 of your normal TDEE two calendar days of the week. YOu can choose to it all by lunch or only at dinner or spread out. It doesnt matter how long in between meals as long as you pick a calendar day and stick to the principle of eating 1/4 however you wish to make up the calories

    Hi, I have a question. If intermittently fast (I stop eating at 8:00 pm every night and don’t start eating until 1:00 pm the following day) will I see results? Should I restrict my calories to lose weight; if so, how many calories should I be eating (I’m female, 20 yrs old). If I follow this regimen and exercise how quickly will I see results?

    Are there any changes you think I should make to this plan?


    Hi mr and welcome:

    You only lose weight if you cut calories. Not eating for any particular time period means little for weight loss.

    This thread will answer most of your questions: https://thefastdiet.co.uk/forums/topic/the-basics-for-newbies-your-questions-answered/

    Good Luck!


    A 24 hour no-food fast is a legitimate fast that does result in fat burning, so a bit confused why you dismiss it.

    If your body can store a day’s worth of glycogen (say, about 12 hours worth) then once this store is depleted (after 12 hours if it’s full, less if you’ve been watching your carb intake) then the body will turn to it’s fat stores after this time. So in 24 hours you can get a good 12 hours or more, depending on how much you had stored in the body to start with, of fat burning. This is what true fasting is – the point where your body uses stored fat as opposed to food being eaten or glycogen reserves. It’s the switch to using fat stores which also triggers the “stressors” which help with Tue regenerative benefits.

    As you point out, if you gorge afterwards you’ll probably end up storing it all as fat again, but it’s wrong to say you have to eat your TDEE or you’ll not lose as so many studies are now disproving that calories are all the same (as ‘Escape The Diet Trap highlights convincngly). So, if you eat with these new food combining techniques in mind and go easy on the carbs before a 24 hour fast you can have a genuinely successful true fast, where you have burned some fat and allowed enough time (because time is important) for the health benefits too.

    Feel free to disagree, I just feel this advice is based on a little old school science which more people are moving away from and the wrong use of the term fasting for 5:2, as fasting has always meant a period of not eating at all, not a period eating a small amount of calories.

    Hi Jo:

    You can burn fat without getting close to ketosis – low fat, high carb, eat at least 6 times a day diets have proven that for years – so a fast is not necessary for ‘fat burning’. A calorie is a scientific standard of measurement, just as a gram or an ounce is. Grams are not different, ounces are not different, and calories are not different. If you eat too many of them, you gain weight. If you eat fewer than you need, you lose. There are no studies I am aware of that show a person can eat to their TDEE calorie number or greater and lose weight, or eat less than their TDEE in calories and gain (we are not talking about water weight, which can be gained from eating carbs).

    Everyone fasts between dinner and breakfast, so we are looking for proof that an additional fasting period of a few hours provides measurably more benefits than those provided by the standard ‘overnight’ fast. Please feel free to give me citations to clinical studies showing that fasting for a few hours is medically beneficial to large numbers of people – and exactly what medical benefits and their results (longer life?) we are talking about. I have asked many with your beliefs before, but never been provided with any – just references to currently popular diet books and TV shows.

    People just seem to want to make weight loss so complicated and difficult. They come with so many false theories. But when all is said and done, it simply comes down to the fact you have to eat less to lose weight. Virtually every weight loss diet ever invented (that actually causes weight loss, anyway) has the person eating less than their TDEE, regardless of the types of foods being trumpeted as the next, greatest, best diet foods on the planet. 5:2 restricts caloric intake by restricting calories two days a week. 5:2 can be defeated by eating more than your TDEE the other five days. 24 hour fasting does not restrict calories by itself, the person has to eat less outside of the 24 hour period to insure weight loss. You acknowledge that by noting that if a person ‘gorges’ they will not lose weight.

    You seem to think ‘old school’ science is wrong. But I have never seen ‘new school’ science that refutes it. The less you eat, the more you lose. It is that simple.

    To be fair, there aren’t enough legitimate trials of human beings to support anyone’s views about fasting! The majority of studies have been carried out on animals. there is a lot of qualitative information around forums mostly (granted, not legit!) suggesting just as many people have no special health changes or significant weight loss following 5:2 the correct way as any other diet does.

    Dr John Briffa has included information about all the studies he references in the back of his book (forgive me, but I really can’t sit here typing them all out!), but I’m open to thinking he (and other popular authors with the same arguments) are selective with their choice of studies to include.

    I’ll certainly try to do some more reading and take into consideration your information, thanks.

    Hi Typhoon and welcome:

    It is always nice to see a newbie ‘discover’ something – I see you posted the links all over the site.

    I believe I was among the first to post Dr. Fung’s lectures on this site well over a year ago now. I am very familiar with his work. I think some people get mixed up when first finding Dr. Fung because they don’t realize he is explaining how the body processes different foods and why that can lead to weight gain (or loss). But even he in his lectures acknowledges that calories in/out is the basic rule.

    There is no research anywhere that says you can lose weight by consistently eating your TDEE or more, or gain weight by consistently eating less than your TDEE. When it comes to weight, the one and only thing that leads to weight gain is eating over your TDEE for a meaningful period of time, and the only thing that leads to weight loss is eating less than your TDEE for a meaningful period of time. Hormones certainly impact weight gain and loss, but they do it by changing the body’s TDEE – not by magically causing fat weight gain. Fat cannot be created out of nothing – there has to be something from which to make it!

    Dr. Fung points out that if you eat certain foods, the body processes them quickly, and deposits them as fat if they are not immediately used. The body is then ‘hungry’ again, and demands more food. The net result is that the person eats more than their TDEE and gains weight. On the other side, some foods are processed slowly by the body, causing the body to not be hungry for longer periods of time with the result that the person eats less. This is how the Atkins diet works, for instance. People on the Atkins diet eat all of the fat and protein they want, but lose weight. That is because they are consuming fewer calories than their TDEE – even while eating ‘high calorie’ foods like fat.

    Science has now determined that one of the basic causes of the obesity epidemic was the low fat diet. That is because people constantly ate foods (processed carbs) that were quickly digested, deposited as fat, leaving the person hungry for more. This, of course, resulted in weight gain, diabetes, heart disease and cancers. Also, we now know that processed carbs like sugar and flour are addictive, making it very hard for a person to lose weight and keep it off – after (or during) the diet, the addiction kicks in and people go back to eating like they had been before their diet, regain the lost weight, and usually more. If you look around this site, you will constantly read about people that binge (always on carbs, not chicken or cheese), or report they had a bad diet day because they ate cake, or whatever, and then couldn’t stop eating.

    Sadly, the only way to lose weight is to eat less than your TDEE over a period of time. While it is much more healthy to eat fat and, to a lesser extent, protein, the fact is that you can lose weight eating pure sugar all of the time – if the sugar calories you are eating are fewer than your TDEE. That is the genius of intermittent fasting – it works for all foods, so a person does not have to radically change the types of food they eat to lose weight so long as they diet for two days and eat their TDEE or less on the other five.

    I wish you Good Luck!

    Thanks Simcoeluv…. thanks for your well formed and thought response…

    At the moment, this IF stuff is amazing… However I do have several question that maybe you could answer…

    on my NFD’s i’m skipping breakfast and trying to do a 19/20:4/5 – so eating window of 4 hours…. I generally eat a 2pm lunch, spinach, etc… I then have a normal dinner ween 6 and 7 (with the family)…. I know i’m not eating anywhere near my TDEE of over 3K per day…..

    Twice a week I extend the fast to a full 24 hours… So miss the 2pm meal. I then just have one meal after the full fast, and then something again the following day at 2pm.. I perform a short 10 min of HIT.. 2 min prep with 3 x 60 sec intensive, 90 secs recover…

    if my scales are right, I started last Saturday at 20st 11.. and this morning i’m at 20St 5.2lbs… I understand the bulk of this would be water. But this seems truly amazing…


    the burning questions for are…..

    Q1 -with the calorie reduction due to the 24 hour fast, and removal of a meal on the 20:4… Will my body be reducing my TDEE like on a calorie reduced diet (bad).. or will the TDEE continue to drop due to my lower body mass (good)

    Q2 – I am tempted to go on a 2 day fast this week, in the hope that will reduce my Insulin resistance further (based on Dr Fung’s research).

    Q3 – I love my zero cal diet drinks and consume far too much.. can have a 2litre bottle easily each day.. I have now restricted this to after/during my meal window.

    What do you think ?

    Hi Typhoon:

    I think you are making a very simple diet much too complicated.

    If you read the post that started this thread, you know when you eat makes no difference. If you look at the components that make up TDEE, you will see that when and how much you eat do not factor in to how TDEE is computed. You seem to be worried about the famous ‘starvation mode’, which is a myth and does not exist in overweight or normal weight people (see FAQ, above). TDEE basically changes with weight and exercise, so the less you weigh, the lower your TDEE. Exercise is a factor, but does not help much with weight loss. How much or how little you eat, or when you eat, are total non factors in determining a TDEE.

    A back to back day fast actually gives you less ‘fasting’ time than non back to back diet days (just figure out the hours and you will see). In addition, you are mixing insulin resistance with a diet. Unless you suffer from insulin resistance, there is no need to worry about it when doing 5:2. And if you suffer from it, then doing 5:2 correctly will lower it without you doing anything special to help it out.

    You can eat/drink anything you want on 5:2 as long as you stay within the calorie guidelines. Zero calorie drinks are fine.

    This thread will answer most of your questions: https://thefastdiet.co.uk/forums/topic/the-basics-for-newbies-your-questions-answered/

    Good Luck!

    Hi Simcoeluv,

    I have tried the 5:2 diet last year with good success – lost 9 lbs in 9 weeks. I would like to try the 4:3 plan for quicker results.

    I need my coffee first thing in the morning, so by having my coffee on any day with stevia and cream by 6:30am and not eating breakfast until 11am (16:8) will this result in slower results?

    Hi Lorelee and welcome:

    It makes no difference when you eat. What matters is how much you eat. This link will explain how much more you might expect to lose doing 4:3 rather than 5:2. https://thefastdiet.co.uk/forums/topic/tdee-for-the-curious-or-why-dont-i-lose-weight-faster/

    Good Luck!

    Hi. I just want to make sure I’m grasping these concepts correctly. I am a 21 year old male, lightly active. If I wanted to follow the 5:2 approach by having one of my fast days be an herbal tea only fast, the other fast day being a 500 calorie fast, and the remaining 5 days follow a diet of 1200 calories, is this sufficient? should my calorie intake on non-fast days be a bit higher? I’ve read that 1,200 is the lower limit but also that 1,500 is more ideal for men. Thank you!

    Hi Xander and welcome:

    The basics are that you eat 600 or fewer calories on your diet days, and your TDEE or less on your non diet days. The quickest way to lose weight is to eat nothing at all (not recommended). You do not give your TDEE or your weight and how much you want to lose, so generic information is all I can offer.

    So compute your TDEE – remembering it is an estimate only – do your diet days any way you want as long as you stay under 600 cal., and adjust your non diet day intake so it equals or is less than your TDEE and at the same time allows you to feel OK. 5:2 is a drastic change to most people’s eating pattern, and it takes the body about a month to adjust. There is quite a bit of ‘wiggle room’ within 5:2, and everyone has to adjust within its parameters in a way that ‘works for them’.

    Having said all of that, your suggested eating amounts are very low and may be hard to maintain for any length of time.

    Good Luck!

    Hi simcoeluv,
    yep, the only way to lose is cut calories, but its what keeps the diet industry going is always the promise of an easier way to lose weight!.I use 4:3 and 16:8 and an overall calorie limit on the week.im losing 3.5lb a week, but my overall average is only 1200 cals a day.
    My own experience is that 16:8 is a great strategy for dieters,in that even with a calorie allowance of say 1000, thats two good 500 cal meals. Im also doing the 4:3 and 16:8,because back in october i was diagnosed with type 2, and im trying to reset my insulin response. Here in the UK doctors only offer medication and the promise that type 2 is a progressive disease. Im 5’11” and at the beginning of october i was 238lb, now im 206 and by the end of march i will be around 168lb. I will see what the blood work says then, if i still have it , i will do alternate day fasting, if that hasn,t worked over 6 months, then its the water fast for me!
    Again, only a personal opinion, if you are looking to lose a lot of weight 16;8 is a great tool as is the 5:2, but only if you count the calories on the other days. The danger is that obese people wont stick to something when they only lose 1-2lb a week.As you have pointed out in previous comments, you do get used to fasting and its not really a problem. When i have dieted before, i used to get headaches and be mentally slow.Now i have plenty of energy and no effects except cold hands and feet!

    i should add that my diet is low carb, a must for insulin control. Even if you dont have type 2, ditch the refined carbohydrate, so no bread, pasta , rice or sugar of any kind, or anything coated or made with flour.

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