It is the entire phrase "things to do and places to be" that you need to understand the meaning of.
This is an English idiom, and it basically means you are busy.
It would normally be used like this:
I have things to do and places to be.
Some people may also instead say places to go.
Usually it also carries an undertone of impatience; that is it may be said to someone who is wasting your time. For example:
Can you hurry up? I have things to do and places to be.
In your example it is used in a slightly different and interesting way. Rather than expressing impatience with somebody else, the writer is using a familiar idiom to describe the reader as a busy person who can't afford to follow a diet/exercise regime that will leave them with too little energy to get things done.