how to calculate fast hours in 24

This topic contains 5 replies, has 5 voices, and was last updated by  minority 11 years, 1 month ago.

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  • I am confused about how many hours in 24 are fasting hours.  At one point in the book, an example is given of someone who eats at 11am and again at 7 pm.  This is said to be 16 hours of fasting.  How?  11 to 7 is 8 hours.  If you take only 1/2 hour, for example, to eat , and you eat twice in a 24 hour period, then why isn’t that 23 hours of fasting…23 hours of not eating?


    I used to start fasting at 8pm say monday, then have 150 cals at 730am tues, then nothing til 6/7 350 cals pm tues eve then next non fast meal will be wednesday am breakie. so thats around 35 hours. i found that having the food at 730am makes me hungry , so this week i have fasted from 8 pm monday had lunch at 1pm tues then tea at 6/7 pm then carry on the same til wed morning, you have done two sleeps so makes the fast a good long one but only limiting your body to the 500 cals. You just count your start  and end fast time, when you choose to have your 500 cals is up to you , everyone is different just try to leave as long as you can in between the two meals. Hoped that helped it does take some sorting in your mind

    I think this needs to be clarified, as fasting should equal no food. Once you eat something, you break the fast, IMO. If you are just trying to lose weight then I expect it does not matter but if you are trying to reap the other suggested benefits of fasting then it matters very much. I also do not understand how eating two or three snacks throughout the 24-hour period can be called fasting and be on the same level as not eating anything for 24 hours.

    Hi, minority – As I understand it, one gets the health benefits if one fasts for a period of at least 12-14 hours.  Don’t forget that one normally sleeps for a large chunk of any 24-hour period.   So, if one thinks in terms of Sleep-Fast-Sleep, one has at least two such beneficial periods of no food intake (including the hours one is sleeping) over a span of 36 hours, with one’s fast day in the middle.  Thus, if Monday is one’s first fast day of the week, one actually starts fasting from the last food intake on Sunday night, say 7pm for example, then there’s Sleep until Monday morning.  If one has breakfast at, let’s say, 8am then that’s a 13-hour fast.  (Some people choose to skip breakfast and wait til lunch, say 1pm, before using any of their fast day calorie allowance, so that would be an 18-hour fast.)  If one then ate again at 7pm on fast day, Monday, but had nothing more overnight until breakfast at 8am on non-fast day, Tuesday, that would be a second fast period of 13 hours.  There are all manner of  possible timings, including going a full 24 hours without food, if one so chooses.  What matters is to find a fasting scheme that suits one’s individual temperament and weekly timetable so that one can happily sustain one’s efforts in the long-term.  I think things can get a bit too rigid when the word ‘should’ creeps in and the pressure of such an imperative can become unhelpful in the long-run.

    thanks jeanius, that helps


    Hi, Jeanius, thank you for your reply. Yes, it is the flexibility which I find so appealing about 5:2 and why I think people are more likely to stick with it. However, at the moment at least, the flexibility seems to extend to the science as well. As far as the benefits of fasting go, I have read articles and research reports quoting 3 to 4 hours, 7 to 8 hours, several days and something in-between. It surely can’t be all of them!

    What I have personally settled on is eating all my calories in one go; as other people have also mentioned, eating a little in the morning actually makes me more hungry than not eating at all. So I have my evening meal at around 9 pm and then I eat at 8 pm the following day and then I have my normal breakfast at about 10 am the third day (I can’t eat too early in the morning). The only thing that breaks my strict 23-hour fast is white coffee in the morning, about 8 am. And I would very much like to know how much impact the milk has on the chemical changes in my body which are going on during the fast – I don’t seem to be able to find an answer to that. There is obviously lactose in it but does it affect glucose levels the same way as other sugars? So either I am doing a straight 23-hour fast or I am breaking it after 11 hours the same way as someone having some of their calories for breakfast.

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