"Neither skinny nor fat" 用英语可以说成 "neither underweight nor overweight"。
"Neither" 是 "not either" 的缩写，意思是 "既不是这样也不是那样"，"underweight" 意思是 "体重过轻"，"overweight" 意思是 "体重过重"。
下面是一些例句:
He's neither underweight nor overweight, he's just right.
(他既不是太瘦也不是太胖，正好合适。)
She's neither skinny nor fat, she's in perfect shape.
(她既不是太瘦也不是太胖，身材非常完美。)
He's neither underweight nor overweight, he's at a healthy weight.
(他既不是太瘦也不是太胖，体重健康。)