The FastDay Forum

900 in 12 hours or 75 cals/hr overnight seems reasonable, by 10 pm you've digested 1400 calories and used 150 so put 1250 in the tanks. By 8am 750 have been used leaving 500 in store.

After breakfast you're using 125 cals/hr so by noon you've used up breakfast and are back at 500. 125 are taken out of store to get you to lunch which then powers you until 5pm, leaving 375 in the tank. This fuels you for the three hours to dinner.

Seems reasonable.

Your 200 cal fast day meals are used up within 2 hours and hence create a deficit period until the next mini-meal. Personally I'm inclined to skip breakfast to stretch out the deficit period to a longer stretch, on the basis that blood sugar, insulin etc will get bottomed out and "do more good".

I'm not sure that there is a simple answer to this as the concept of weight loss is complex.

If you are trying to determine the exact time at which weight loss occurs, you need to be a lot more specific about what you mean by weight loss. After all, you lose weight when you visit the loo, but I'm sure that's not what you mean. In the short term, my body will respond to a calorie deficit by using available glucose - but there's only enough of that for a few minutes. In the slightly longer term it will start using glycogen from my liver. It can cope for a number of hours on that. It's only when the glycogen starts to run low that I start to consume energy stored as fat. Now that's what I call weight loss, but other peoples definitions will vary. As I understand it, my glycogen has to be low for some time before I start using fat - I don't think that it's a matter of weight loss starting as soon as I have a calorie deficit.

Don't know if any of this helps answer your question, though.

Mike

It's only when the glycogen starts to run low that I start to consume energy stored as fat. Now that's what I call weight loss, but other peoples definitions will vary. As I understand it, my glycogen has to be low for some time before I start using fat - I don't think that it's a matter of weight loss starting as soon as I have a calorie deficit.

You burn fat all the time, at least if your heart rate is under 120 or so - as you work harder above that the percentage from carbs rises rapidly to practically 100%.

You only exhaust glycogen reserves by high intensity exercise, then you "hit the wall".

Seems a good way of looking at it.

It isn't precisely correct because you burn body fat whenever more fat is being used than you have eaten recently, so fat comes and goes from reserves practically all the time. After a low fat meal for example you would be likely to be burning body fat.

If you dig into "postprandial substrate oxidation" you'll be able to geek out on respiratory quotients and the like.

I came to a similar conclusion looking at fast timings, if you have a normal lunch and then a reduced dinner and go back to normal dinner the following day the period of deficiency is extended. This mainly arises from the large intake at dinner.