Asking for a friend. 
This morning I was going to eat so I had a bit of some protein bar (Keto friendly) and then I was like nahhh I’m really not hungry. Do you think the one bite would have broken the fast ?
Can you break a fast by taking one bite of food?
RobC
(Robert C)
#2
Of course (technically speaking) it broke a strict water fast.
Maybe also slowed or stopped any gains you might have been getting from autophagy.
But, in terms of fasting generally (for fat loss, not slowing metabolism, improving hormones etc.) - it will not make any difference. Your body will not perceive that one bite as some new low daily calorie level it should slow its metabolism to attempt to meet.
Instead, it is going to be a tiny pause in the otherwise great things fasting is likely doing for you!