I don't eat fast food. That is like poison to your body. We eat to maintain our bodies and fast food, while it can taste good, has no nutritional value in it. In fact, it is full of sodium and cheap meat, overly processed white flour (buns) and way too much cheese.
But I don't eat it for me, because I don't believe in eating that way - I don't tell other people how to eat. I do think it is sad to see little kids whose bodies are growing being fed that rotten stuff - topped off with a soda pop.

It offers them nothing their little bodies need.
Your baby will be fine. A fetus takes everything from the mother. He isn't going to suffer if you have taco bell every once in awhile.