Find variables in a function that depend on a certain variable

I have a function with many calculations in it. I want to identify all the variables within that function that were calculated from a certain variable, even indirectly. For example,

bankBalance = 100 ; 
groceries = bankBalance*0.8 ; 
iceCream = groceries*0.1 ;

In this case, I want to identify both groceries and iceCream as variables that depend on bankBalance, even though bankBalance doesn't appear in the iceCream calculation. In reality there are 50+ variables derived from my chosen variable, and 200+ that are not. How can I list all variables that depend on a chosen variable within the function? I could set bankBalance to NaN and see which variables become NaNs, but perhaps there is a better way.