太ってないよ

not fat

→ 太る
phrase Rare #29,377
not fat A casual way to reassure or point out that someone is not fat or overweight. 太ってない is the conversational form of 太っていない, and よ adds emphasis.
JA: 心配しなくていいよ。全然太ってないよ。
EN: You don't need to worry. You're not fat at all.

太ってないよ

You're not fat.

トムあまり太ってないよ

Tom isn't very fat.

トム前ほど太ってないよ

Tom isn't as fat as he used to be.

トムそんなに太ってないよ

Tom isn't that fat.