"I eat" and "I am eating" are not really interchangeable.
you use "I am eating" when you eat at the time you speak: now, I am eating an apple
you use "I eat" to express a constant action or a habit: I eat an apple every morning
In French, there is no verbal form for the continuous be + VERB-ing, but there is an expression that can easily replace it:
I am eating = je suis en train de manger
I eat = je mange