Why no carbs after a fast?

I started fasting because I wanted my gut biome and body to reset and for autophagy, plus the weight loss (big thing) I just finished day 4 planning on doing either 7 day or 14 day fast, I’ve fasted multiple times in the past and failed miserably and went to get junk food right after. My question is I wanted to go to a sushi buffet the day my fast is over (will probably aim for 14 days for sure will knock out 7). How bad is this? What will it do to my fat storage and stomach biome ? Any advice? I think my body can handle the random food I never got sick or bowl issues before when I did a 4ish day fast in the past.