Can we use "Now" for a present habit because we mentioned a past habit previously?

Question

It is ok to say:

I don't eat fast food (a present habit)

I ate fast food when I was a child (a past habit - it no longer happens now)

Now, when we combine these 2 sentences together.

Does this sentence sound strange?

I ate fast food when I was a child but I don't eat fast food

Can we say:

I ate fast food when I was a child but NOW I don't eat fast food?

Can we use "NOW" for a present habit because we mentioned a past habit previously?

Note: you can use Simple past tense to express past habits

USE 4 Habits in the Past

The Simple Past can also be used to describe a habit which stopped in the past. It can have the same meaning as "used to." To make it clear that we are talking about a habit, we often add expressions such as: always, often, usually, never, when I was a child, when I was younger, etc.

Examples:

I studied French when I was a child.

He played the violin. He didn't play the piano.

Did you play a musical instrument when you were a kid?

She worked at the movie theater after school.

They never went to school, they always skipped class.

Answer 1

I ate fast food when I was a child but I don't eat fast food

does sound a bit strange.

I ate fast food when I was a child but NOW I don't eat fast food

is better.

I ate fast food when I was a child but I don't eat fast food now

places the word "now" where I would normally expect to see it.

I ate fast food when I was a child but I don't eat fast food anymore.

is more what I would expect to hear in everyday conversation or see in typical writing (replacing "now" with "anymore").

"Now" only describes the current state. "Anymore" does that while at the same time comparing to the past. "Now" is not wrong, but it would not be the usual choice in this situation.