I avoid all artificial sweeteners aside from a few plant based ones like stevia.

Technically, no sugar very low/no carbs don’t break fast.

But drinks like g zero have ingredients like starches and artificial sweeteners, which if you research the keto diet, your body basically processes just like sugar. Both are bad for insulin levels, could stop ketosis, and may be bad for autophagy.

Which is why processed foods with starches are very unhealthy even when they brag about being sugar free.

Do you, but I personally avoid always, not just when I fast as I try to stay in ketosis even when not fasting