Which term describes the act of maintaining optimal body function?

The term that best describes the act of maintaining optimal body function is "wellness." Wellness encompasses a holistic approach to health that includes physical, mental, and emotional well-being. It is not just the absence of disease but involves actively engaging in practices that enhance overall quality of life and promote good health. This includes lifestyle choices such as exercise, diet, sleep, and stress management, all contributing to optimal body function.

While health refers more broadly to a person's medical status or absence of illness, and fitness typically denotes physical capabilities related to exercise and activity, wellness integrates these aspects and focuses on overall life satisfaction and balance. Nutrition, on the other hand, specifically pertains to the substances that an organism consumes, which are essential for maintaining overall health but do not encompass the broader concept of wellness on their own.