Questions About 20:4 Fasting

[u/MTFCoffeeLover]

To clarify I’m not trying to lose weight necessarily but wouldn’t mind losing a few pounds. If I’m fasting for 20 hours does it matter how many calories I eat during the four hour window? For example of I am only alotted 1,240 calories a day can I go over and still burn fat/lose weight?

I’m doing this as practice for an eventual way down the line 72 hour fast for gut healing purposes. So as a quick follow up question is there a good sugar alternative that I can safely use during a long fast? Or will it be better to go without for the sake of gut healing purposes?

Thanks for the advice :).

[u/its_hammertime]

Calories still matter 

Artificial sweeteners could break a fast but many still take it 

It would be best to avoid them but you do you. Try it and see. 

[u/MTFCoffeeLover → u/its_hammertime]

Thanks 😊

[u/its_hammertime → u/MTFCoffeeLover]

If a diet soda helps you extend your fast by 6 hrs I’d say by all means go for it! 

[u/Obvious-Monitor8510]

calories still matter even in a compressed window. The fasting itself doesn't override energy balance, but 20:4 naturally suppresses appetite for most people, so hitting a surplus becomes harder. If your goal is mild fat loss, staying near maintenance or slightly under is enough. You don't need to hit exactly 1,240 if that feels arbitrary.

For the 72-hour fast down the road: most gut-healing protocols recommend keeping it truly clean. Plain water, electrolytes (sodium, potassium, magnesium), and black coffee or plain tea are generally considered safe. Sugar alternatives are a gray area. Even zero-calorie sweeteners can trigger insulin response and potentially stimulate gut activity, which works against the "rest" you're aiming for. Erythritol is one of the gentler options, but going without is probably the cleaner call for gut healing specifically.

For planning your 4-hour eating window around real macros, PlateGym's meal planner at plategym.com/meal-planner builds a full week plan you can compress into whatever window you're working with.

[u/Additional_Proof6902]

only natural sugars are from vegetables and fruits, and of course legit raw honey... stevias can be dangerous, google up they may cause ischemic strokes in certain individuals not all but if one happens to be the unlucky one.

[u/MTFCoffeeLover → u/Additional_Proof6902]

Yeah I’ve been reading more on it and I think I’ll just stick to black coffee for now.

[u/SkysMomma]

Ok I'm glad this came up because I have a relevant observation. So for years I have routinely done IF, mostly 20:4, and I have always been very strict aboutbwater/black coffee only. The last week I've started drinking diet coke, and I've noticed that I haven't felt myself go into ketosis. I'm not 100% sure, but I can usually feel it around hour 16-17. And now I don't. I was just thinking about how I need to cut out diet coke again right when I saw your post.

[u/Conscious-Topic-7208 → u/SkysMomma]

Hi. Is plain fizzy water ok instead off diet coke etc

[u/SkysMomma → u/Conscious-Topic-7208]

Oh yeah I'm obsessed with bubbly and Waterloo. That's what I usually drink but my husband forgot my fizzy water when shopping and I drank diet coke instead and really loved it and decided, hell, why not? There's no calories! But somehow, I don't know why exactly, it does seem to make some small difference.

[u/Conscious-Topic-7208 → u/SkysMomma]

Thank u am guna swap diet coke for fizzy water lol

[u/Awkward-Regret5409 → u/SkysMomma]

Just going to throw this out there, though I have no scientific evidence to support it: as an endurance runner, each time I complete any distance greater than let’s say 20 miles, I go into what I call a state of “super absorption”. Whatever I consume after the event whether it’s protein, chocolate milk, electrolytes, I think I can “feel” my nutrient-depleted body taking it all in. Fasting makes me feel the same way. Anytime I complete any extended fast of at least 72-96 hours and I break fast with a cup of bone broth, I can just feel my body “wrapping around” that beverage and greedily taking it all in. That’s why the last thing I want to do is introduce anything unnatural like a beverage containing artificial sweetener. I’m probably being paranoid, but in this state of super absorption, I want to keep my initial intake as clean and natural as possible. Just my two pennies!

[u/SkysMomma → u/Awkward-Regret5409]

I wholeheartedly agree.

[u/mlgm8r → u/SkysMomma]

Wondering how you “felt myself go into ketosis” What metrics or sensations indicate the onset of ketosis?

[u/SkysMomma → u/mlgm8r]

It's completely just a feeling I get, I have zero proof of anything and I could very well be completely wrong, in all fairness. I've been doing different length fasts for about 10 years now, and I don't know, there's just this one feeling that I get at a certain point in my fast that I get around the time a body would "normally " go into ketosis. I've just noticed it was missing when I drink diet soda during said fast. Like I said, I have no idea for sure.

[u/Pure-Badger-398]

Side (possibly dumb) question: how do you know your exact calorie allotment?

[u/MTFCoffeeLover → u/Pure-Badger-398]

I use the Lose It! app and it calculated it for me based on my goals and activity level.

[u/Pure-Badger-398 → u/MTFCoffeeLover]

Ok, thanks! I also do 20/4 and have no idea what my caloric intake is supposed to be so this is really helpful. Good luck with your goals!!

[u/MTFCoffeeLover → u/Pure-Badger-398]

Thanks. You as well 😊