保持身材英文是Keep fit。
例句：
1、我一直注意保持身材。
I have always paid attention to keeping fit.
2、她的新年决心是要保持身材健美。
Her New Year's resolution is to stay fit.
3、他经常运动，以锻炼身体和保持身材。
He exercises regularly to workout and maintain his physique.
4、她要保持身材苗条，就不得不节食。
She has to diet in order to stay slim.
5、很多人希望保持身材苗条，但同时又担心自己的健康。
Many people want to stay slim, but at the same time they are concerned about their health.