Well I personally think it's a myth that even consuming absolute zero carbs would allow you to burn bodyfat when you are consuming more (fat) energy than you are burning. The people who report it (I think Regina did recently) are forgetting that on very low carbs on a calorie surplus, they will actually tend to be storing some of those excess calories (as bodyfat)so it's 'new' bodyfat that will need to be burnt first (before net bodyfat loss can occur) when a calorie deficit is established, Which will give the impression that a calorie deficit has occurred at a higher calorie intake, when in reality no such change has occurred.

Anyway, I wish you success in establishing a net calorie deficit over time and having the fatburning enzyme machinery ready for bodyfat burning action when you do. And while not trying to open another can of worms, you wouldn't consider pushing your normal overnight fast by an hour for the next week or two and just watching to see if you tend to eat more in total over the slightly shortened eating 'window'?. If you don't (tend to eat more in total), it would be interesting to see whether the desired 'calorie deficit' would be getting more of a chance to establish for a bit longer each day.

Remember, over any given eating/fasting cycle (and bear in mind that everybody intermittently fasts to some extent every day of their entire lives) you can concievably be in calorie deficit for some proportion of it, and in calorie equilibrium/ surplus for the the rest (ie for however long it takes after food is last consumed for those calories to be consumed). If while you are in calorie surplus you don't tend to store any new bodyfat because you have set up a hormonal environment not conducive to bodyfat storage with a low carb dietary approach, then when whatever time is necessary to exhaust FFa's/ketones from dietary fat has elapsed before you eat again, you will necessarily begin to burn bodyfat.

If OTOH, you eat again before dietary fat (and whatever carbs you have consumed) has been exhausted, your body simply won't bother going after bodyfat. Why would it? It's much more difficult to get bodyfat out of storage than just burn the dietary fat (or carb) that's immediately available.

Stuart