Every fast is unique, even for the same person. Your eating habits days before the fast will impact your hunger levels, your “experience level” at fasting will make a difference (it gets easier the more you do them), the length of time you’ve spent eating keto will make a difference, the amount of body fat stores you have to lose will make a difference.
In summary, there are MANY variables and your fast will be unique to you.
Try the “sea salt on the tongue” trick Megan Ramos describes, it might help cut the hunger.
The hunger WILL go away, but when that happens… it’s different every time for me.
I can’t speak about the breathilzer but, after 4 days, you are surely deep into ketosis, do you have “metal mouth” or a strong odor to your urine? Those are classic signs of ketosis, especially when you first start fasting (they go away after you’ve been doing keto/IF/extended fasts for a while).
If you are only feeling hunger, and no other “negative” side effects, push through to the 5th day, you’ll be glad you did, no regrets from giving in. Eventually, you’ll hit an almost euphoric state, one where you’ll think to yourself “I can do this forever!” and then, a few hours/days later, you’ll feel like crap and might even slip back into the keto flu feeling, my hypothesis is that we burn fat slowly and when the body is busy burning it, we feel good/don’t feel hunger but, once that fat store is almost totally gone, we start to feel weak/hunger, until the body is able to fully metabolize another “unit” (fat store) of energy, at which point we feel better.
Best of luck to you!
- Complete guide to fasting by Fung
- Personal experience
- Lots and lots and lots of youtube videos/podcasts etc…