whats the difference between morningcardio and regular cardio?

[Tatyana]

The body rarely uses one source of fuel exclusively, and it isn't like there is this on/off switch, oops carbs, stop using fatty acids.

It doesn't work like that.

That being said, I am pretty sure most biochem textbooks would state that liver glycogen stores are depleted overnight.

That is typically 200 g so approximately 800 kcals, which would seem like enough.

 

[desmond]

Where did you read this, that fat is the primary source of fuel
while asleep? Not only does your metabolism slows down while asleep, but your whole body too, and those extra carbs that you consumed before going to sleep will turn up in your midsection.

Think about it - the lower the intensity of activity, the more fat si used as a % of cals, therefore, fat is the primary source of energy.

Burn Fat While You Sleep (I have seen more scientific studies on this b4 but couldn't find them now through a quick google research)

Tat: I'm doubting u burn 200g of carbs overnight (u don't burn 800 cals overnight; and presumably carbs are at least < 50% of energy fuel used over night). If we burned 200g of carbs overnight, u'd need to consume a large box of oatmeal pre-bed to get through it lol.

My thinking is if carbs constitute 20% of energy use overnight (per link, and what I have read before), that's 120 cals of carbs, or 30 g of carbs overnight, as about 600 cals are used across an 8 hour sleep for an 80 kg man: see How Many Calories Are Burned ...? (note this also equates to about 50 fat grams).

But my understand also was that liver glycogen was closer to 100g not 200 (see Glycogen - Wikipedia, the free encyclopedia which suggests 100-120g; Bodybuilding.com - ISSA - Does Fruit Make You Fat? which states 100g);

Hence, overnight fast would cause mild liver glycogen losses but no muscle glycogen depletion. I thought the latter would be more relevant to whether u burn fat/carbs during exercise (as muscle glycogen is the primary supplier of exercise energy) but this is merely personal conjecture.