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 bennyboy:

    16:8 has always fascinated me. It started as a miracle diet called the 8 Hour Diet. The book claimed that you could eat all of anything you wanted to eat but if you ate it in an 8 hour ‘window’ you would lose weight. When you read the book, you soon found with its special foods and exercise requirements that it was a standard eat less every day and exercise diet book. It went the way of all fad diets until IF came along, when it was resurrected as a ‘fasting’ diet.

    A person can easily eat their TDEE in one sitting lasting less than an hour, so eating in an 8 hour window carries with it no calorie restriction. And people can easily eat twice their TDEE or more in 8 hours, so they have to choose not to eat that much if they don’t want to gain weight. That means people have to make the decision not to over eat, or to under eat enough to lose weight, in that 8 hour period. They also have to make the decision to not eat for the remaining 16 hours of the day. I’m not sure how that is different than a person having to decide not to over eat, or to under eat, with an ‘eating window’ that lasts as long as they are awake regardless of when they eat in that window.

    People generally sleep for several hours each day, and most don’t eat right before bed and immediately upon rising. So most people ‘fast’ for 8 or more hours each day. I am not aware of any research that finds that ‘fasting’ for a few more hours each day provides any material health benefits over the benefits obtained from the standard fasting most people experience.

    So I guess it comes down to a person’s belief that fasting windows are helpful and that unanswerable refrain – whatever works for me. So my position is simply if it works for you, do it. It is certainly not harmful. I prefer not to diet by the clock, as dieting is hard enough already!

    I see what your’re saying, but you eat two meals instead of three, so it really helps. I know im super motivated after the type 2 diagnosis ……………

    Hi bennyboy:

    You eat two meals in 8 hours because you choose to. You could eat three, four or five meals in 8 hours if you wanted to. Or, you could get the same result by eating a meal when you get up in the morning and a second meal shortly before you go to bed at night. 16:8 is descriptive, but has no real meaning. I guess if you ate in the morning and evening, you would be following 12:12 – again, descriptive but nothing else. It is what you eat or don’t eat during whatever your eating window is that matters!

    Yes, i understand what your saying, but missing breakfast gives you more calories to spend on the other two meals, so you don’t obsess too much.Its just a tool.I did the 5:2 a couple of years ago trying to eat three 200 cal meals and struggled.Now its 250 for lunch and 350 at dinner, i find it easier.Like all fasting,now im used to not eating till midday its easy.When i reach my goal weight, it will be the 16:8 that i use to control my weight.Its hard to eat two 1000 calorie meals!.
    But i understand your point if its about weight loss, people cant believe im losing weight when i still drink fourteen pints of Lager a week!,its all been allowed for in my 8500 weekly allowance ( made possible by 3×600 cal fast days).
    I also want to try to reverse my type 2, that’s why i do the 16:8 and don’t eat carbs at lunch either.

    Thank you for this Post. Really has clarified and help me understand. I plan to start tomorrow with my first 500 calorie day and really need to lose weight. I assumed you had to watch what you eat on the non fast days but great to see it in black and white. Many Thanks

    Hi enough
    This is where the 5:2 can be a great tool for you.Lets say you will lose around 2lb a week on 1200 cals a day.So you eat 1000 cals combined on your two fast days, that leaves you 7400, which means you could have 1480 on the remaining five days! Or, eat 1300 on the non fast days, its gives you 900 to spend on going out ( red wine 130 cals for a 175m glass, thats seven glasses, so Fiday and saturday night sorted lol !)Please note im not encouraging any alcohol intake!.
    If you dont eat bread, rice or pasta or any sugar,1480 is three very good meals:Remember, 5:2 will only work if you consume less calories than you expend over the whole week
    Good luck

    Hi enough and welcome:

    This thread is a subset of a thread that will answer most of your questions on 5:2: https://thefastdiet.co.uk/forums/topic/the-basics-for-newbies-your-questions-answered/

    If you have a question not answered on the thread, ask!

    Good Luck!


    Report of a couple of studies indicating calorie restriction is good for normal weight people, too: http://www.foxnews.com/health/2016/05/03/calorie-restriction-may-have-some-benefit-for-non-obese.html


    Most studies to date show that calorie restriction yields the health benefits associated with fasting. However, some believe time between meals yields equal or better benefits than calorie restriction. This study, authored by Longo, Mattson and others, compared three meal a day people with one meal a day people (23:1) and concludes:

    “The present findings suggest that, without a reduction in calorie intake, a reduced-meal-frequency diet does not afford major health benefits in humans.”

    Other interesting results were observed.


    I know you don’t believe there is any added benefit of longer periods between meals, but the Longo et al paper appears to suggest there are indeed benefits.

    You have been very selective with what you quote (and don’t!) from the conclusions.

    It was admittedly a very small study, and the one meal per day group were aiming to eat TDEE in one sitting (which most of us here that practice sone form of longer fasting don’t). Subjects were healthy normal weight. Also it was time-limited, and the authors acknowledge that the duration may not be long enough to result in stable changes in physiology.

    However, they did find that body weight and body fat decreased on 1 meal/day, possibly explained by the effect eating patterns could have on metabolic activity, This would accord well with what Fung says too.

    One meal/day also reduced cortisol. Given what we know about the effect of cortisol on fat storage, this is good news. Sadly the study had some flaws since this may simply be an artefact of sampling time…

    The authors concluded:

    “Consumption of 1 meal/d resulted in weight loss and a decrease in fat mass with little modification in calorie consumption”

    This suggests that for those trying to lose weight, and consuming less than TDEE, reducing the meal frequency would be likely to produce results.

    And actually for those trying to maintain weight, 24 hour fasts are probably a useful tool.

    I take it you’ll be changing your advice to newbies now, from ‘it doesn’t matter how often you eat on fast days’ to ‘there is some evidence that reduced meal frequency may be beneficial to weight loss’.

    jochall>>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 <<<<

    The body stores a lot more than 12 hours of most people’s BMR worth of calories in glycogen, for most people who are already overweight and sedentary even more than 24 hours. Even a couple of hours of cardio exercise thrown into that mix might not hit the storage limit. This is the sort of thinking that keep recreational endurance exercisers fat enough to be here in the first place. Us chubby cyclists, runners, swimmers, triathletes etc commonly outeat any glycogen emptying activities, let alone the sedentary population that thinks not eating for 12 hours equals fasting.

    The liver stores about 120g of glycogen that can be released for general use. So about 450 calories. Muscle about 400g (but the stored glycogen in the muscles is not able to be released for general use, it can only be used by the muscle that is storing it.) No matter what the activity and the intensity of the activity you will use a combination of glucose, glycogen and stored fat. The ratios will vary depending on the intensity and your stored energy distribution at that specific time. I think most people are fooling themselves if they think 12 hours of fasting (or in the context of this forum 500/600 cal) will see them flipping into ketosis (unless they are already following a strict ketogenic diet in the first place). When I first started doing 5:2 it would take me about 60 hours (of water fasting) to flip over to ketosis. That flip now takes 24 hours. I measure this with a blood glucose/keto meter.

    I must admit I haven’t read each and every post in this thread from start to finish, but I’m still a bit confused.

    I was under the impression from reading the book and watching the programme(s) that the 5:2 diet was first and foremost a diet that was beneficial to your health in many ways and that the weight loss was, well, more or less a byproduct.

    As someone mentioned here on the thread: In the book Michael talks about leaving as long a window as possibly between your fast day meals (breakfast and dinner or maybe to skip breakfast and just have one meal). This is supposed to be the start of the body’s recovery mode where cell repair can take place.

    simcoeluv, you say that it doesn’t matter what time of the day you eat on your fast days as long as you stick to your calorie intake, yet you only talk about weight loss and not about the health benefits arising from fasting.

    Can you please clarify this?


    The vast majority of people on this forum are motivated to do 5:2 for the weight loss aspect of the diet. You are absolutely correct in that 5:2 also produces many health orientated benefits other than weight loss. I reached my goal weight back in March and now do 6:1 water fasts on my fast day. This keeps my blood glucose low, typically 4.2-4.4 mmol/L. Keeps my liver function as it should. Depletes my glycogen stores. Cleanses my liver and kidneys. Aids autophagy with cell growth biased towards cells that can run on ketone bodies as well as glucose. My LDL and HDL numbers have improved. Cholesterol has come down etc. etc.

    bigbooty, thanks very much for your reply.
    It probably depends on the age of people too. As you get older, you’re more concerned with staying healthy or improving your health, so for me and my husband weight loss and health benefits are probably equally important.

    Hi Ms and welcome:

    There is a short and long answer to your question. I will start with the short answer. Current research indicates that to get ‘other health benefits’ from fasting you need to water fast for about four consecutive days every month or two. The key seems to be significant calorie restriction over time – not just one four day fast, much less fasting for a few extra hours each day. On the other side, research on the so called 20:4 eating pattern (eat all of your calories in a four hour period each day, and fast for the remaining 20 hours) concluded: :”The present findings suggest that, without a reduction in calorie intake, a reduced-meal-frequency diet does not afford major health benefits in humans.” http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2645638/.

    So it is the significant calorie reduction over time, not fasting between meals, that yields the ‘other health benefits’. However, losing weight, which usually yields lower blood pressure, lower triglycerides and better cholesterol levels, is nothing to sneeze at!

    Good Luck!


    If you haven’t already come across Dr Jason Gung (intensive dietary management, The Obesity Code), you might be interested to read what he has to say on fasting windows. He seems to think even shorter periods of daily fasting have benefits wrt insulin. e.g.

    Thanks very much for the info! 🙂

    Can I confirm that on the fast – 2 days you can eat 500 cal a day and you don’t have to leave 12 hours between meals. I have been doing this for 3 weeks as follow. Get up have 200 cal meal during the day I will have snacks of 100 car and 200 for dinner. Someone told me that I should only have 250 morning and 250 night and nothing all day????? I am doing this for health as well as weight loss. I get that on my 5 days in need to keep within the TDEE range to make it a success.


    On fast days you can break the calories down any way you want, as long as you stick to the 5/600 cal max.
    Regarding ketosis. I did an experiment on the weekend. Friday, 600 cal ketogenic (boiled eggs, stir fried beef with cabbage, zuccini, mushrooms – less than 10g net carbs). Saturday water fast, Sunday nothing until dinner.
    Used urine strips to measure ketosis. Saturday afternoon I was in low ketosis. Sunday morning, optimal ketosis.


    Urine sticks are a little bit too subjective. Buy yourself a good keto meter and measure your blood ketones. I use an optium neo.

    Hi Cathy and welcome:

    bc is correct. As long as you stick to the calorie limitation you can eat your calories at any time you want. My 3 Jan 15 post in this thread cites Varady’s research to that effect.

    Good Luck!

    It depends if you want to stick rigidly with the old advice or accept the latest thinking on longer fasts. MMs latest advice is to delay breaking your fast as long as you can and eat early the previous day too. But basicly this is a flexible approach you can do what suits you. If you can’t stick to it without breakfast have breakfast, but it would be beneficial if you didn’t. Likewise with carbs. It is far better not to have them but if you can’t face life without them you still can but then you should stick to the lower 5/600 calorie per day amount whereas you can have 800 if you eat on the M plan. I have been losing ten pounds a month rarely going below 800, the actual number of calories seems to make little difference as long as they are nutrient dense calories and well below BMR.

    perfect, exactly what i was confused about as a newbie,

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