Use the adjective preventative to describe something that helps keep you free of disease, like a healthy diet and plenty of exercise.
If it prevents illness, it's preventative. You can also use the word for things that hinder you, like a preventative speed bump that keeps you from rushing home to watch your favorite TV show, but it's more commonly a medical or health term. "Preventative medicine," for example, is focused on avoiding diseases rather than treating them. The Latin root word, praeventus, means "to hinder."