Sheila, I had a bit of a muse on that question on thread 15 so I'll repost what I wrote for you. Maybe some of it will help:
---
Can I fast for a 24 hour period say from 1pm to 1pm and just stick to my 5/600 kcal allowance in that time?
I?ve been giving this one a lot of thought. I?ve always thought that if you choose to do a 24 hour fasting period then this is meant to be a zero calorie fast for 24 hours with normal eating either side. This is another form of intermittent fasting.
Personally I?d say that if you choose to do 5:2 then, as others have said, it is helpful to think of a ?day? as a calendar day, not as a 24 hour period. If you need to think of it as a 24 hour period to get your head around it then think of it as midnight to midnight. (You don?t get to choose what time e.g. Tuesday starts, by the same token, you don?t get to choose what time a fast day starts only which days you are going to fast on IYSWIM). Like I said though, this is if you want to do 5:2 and keep it simple. There are other forms of intermittent fasting which are perfectly valid and can work.
Here?s an illustration (not intended to tell anyone what they should be doing, just an illustration) of why it might not be helpful to think of a ?fast day? as a 24 hour period which spreads over two calendar days:
Lady with a TDEE of 1750 kcal per day does 5:2 the simple calendar day way:
Monday fast day eats 500 kcal
Tuesday normal day eats 1750 kcal
Wednesday normal day eats 1750 kcal
Thursday fast day eats 500 kcal
Friday normal day eats 1750 kcal
Saturday normal day eats 1750 kcal
Sunday normal day eats 1750 kcal
Total calories consumed: 9750 kcal
Total calorie deficit for the week: 2500 kcal
Lady achieves this by having on normal days: 400 kcal breakfast, 500 kcal lunch, 600 kcal dinner and 250 kcal for drinks and treats; and on fast days by either having a 16 hour fast until lunch and then having 200 kcal for lunch and 300 kcal for dinner or by having a 24 hour fast and having a 500 kcal dinner.
Lady?s friend, who also has a 1750 kcal TDEE decides to give it a go, but decides to do a 24 hour fast from 1pm to 1pm:
Monday until 1pm 400 kcal breakfast plus 500 kcal lunch plus 100 kcal drinks total: 1000 kcal
Monday 1pm to Tuesday 1pm 24 hour modified fast 300 kcal dinner plus 200 kcal breakfast total: 500 kcal
Tuesday after 1pm lunch 500 kcal plus dinner 600kcal plus drinks and treats 150 kcal total: 1250 kcal
Wednesday normal day eats 1750 kcal
Thursday until 1pm 400 kcal breakfast plus 500 kcal lunch plus 100 kcal drinks total: 1000 kcal
Thursday 1pm to Friday 1pm 24 hour modified fast 300 kcal dinner plus 200 kcal breakfast total: 500 kcal
Friday after 1pm lunch 500 kcal plus dinner 600kcal plus drinks and treats 150 kcal total: 1250 kcal
Saturday normal day eats 1750 kcal
Sunday normal day eats 1750 kcal
Total calories consumed: 10750 kcal
Total calorie deficit for the week: 1500 kcal
(This also assumes that Lady?s friend is not tempted to eat a bigger lunch on the two days either side of her fast and is also not tempted to have more calories in treats either side of the fast)
Each week Lady gets in two 16+ hour periods of zero calorie fasting and reaps the health benefits and has a calorie deficit of 2500 kcal per week which sees her slowly but surely losing some weight.
Lady?s friend doesn?t get in any periods of zero calorie fasting except what every human being gets overnight while asleep and her calorie deficit is only 1500 kcal per week so she may not be getting the health benefits and she begins to get frustrated because it seems like she?s not losing weight very quickly.
I?ve been thinking about how the 24 hour modified fast could still work. If Lady?s friend did, say, 3pm to 3pm instead and so skipped lunch on Tuesday and Friday she could increase her calorie deficit to 2500 kcal, which is the same as Lady?s. If she also had her 200 kcal meal on Tuesday and Friday closer to lunch time instead of at breakfast then she could also get in two 16+ hour zero calorie fasts per week for the health benefits that come along with that.
So I think it is possible to do it.
The downsides though are: a) it?s more complicated that going from sleep to sleep and b) the fasting affects 4 calendar days per week to get in just two fasts whereas a sleep to sleep approach only affects 2 calendar days per week. It also may be true that for anyone who doesn?t want to calorie count at all outside of their modified fasts this approach may not work as these people (me included) may be inclined to eat too much on the morning and afternoon either side of the fasting period for it to work.
But I?m not by any means an expert and I?m just typing out my musings on this so if it works for you, please let us know!
?and if everything I?ve typed above seems way to complicated then ignore it completely and stick to this simple principle:
On a fast day eat no more than 500 kcal (600 for men) from waking up until going to sleep. On a non-fast day eat normally.
That?s it, it really is that simple.
