"I want to maintain/keep/stay healthy" 可以用来表示 "我要保持健康" 的意思。
其中 "maintain" 意为 "维持"，"keep" 意为 "保持"，"stay" 意为 "保持"。
下面是一些使用 "I want to maintain/keep/stay healthy" 的例句：
I want to maintain a healthy diet. (我想保持健康的饮食。)
I'm trying to keep healthy by exercising regularly. (我在努力通过定期锻炼来保持健康。)
I want to stay healthy so I can enjoy my retirement. (我想保持健康，这样我就能享受我的退休生活。)