Food that doesn't have a lot of fat calories is called "low-fat food". People who want to lose weight try to eat low-fat food. You can use "low-fat" in a couple of ways:

Is it low-fat?

I don't like the taste of low-fat food.

"Low-fat" means that an item doesn't have much fat at all. If you're making something, like cookies, that usually have a lot of fat, but your version has less, you call it "lower-fat"