At what point does your choice of meal before a fast stop mattering?

So it makes sense that you want to start a fast with a filling meal that's low in carbs, so you don't end up craving food so easily. But I'm assuming after, say, a week of fasting, this choice of final meal won't still be having any effect on cravings, right? So basically what's the time period one has to get through such that they're no longer feeling any consequences of their final meal?

Answer

Assuming you ate a big, high carb meal, 6-8 hours for food to pass through your digestive track, and 14-16 hours for liver glycogen to be depleted from full. You won’t burn fat until you deplete your liver glycogen stores.

The reason why you start low carb is so that your liver glycogen store is lower, so you start burning fat faster. It’s also helpful with not crashing your blood sugar and feeling like shit. You will likely crave food no matter what you eat before the fast.

Answer

24 hours is probably the limit, but if you are used to eating lots of carbs, your hunger pangs might be more intense, even if they are not longer in duration.

Eating a lot of carbs means your body needs more time to empty glycogen stores in your liver. While your body is using glycogen, you are not burning fat. It takes time for that process to ramp up after your liver glycogen is depleted.