[Idiom] "You never know" is past or present tense?

[Nikki8]

There are many sentences regarding the idiom ''you never know'' but i want to know particularly for these sentences.
Where using *is* is correct.
1) you never know which food is helping you in controlling your weight.?
2) you never know which good deed is saving you?

 

[emsr2d2]

[STRIKE]There are[/STRIKE] Many sentences [STRIKE]regarding[/STRIKE] can include the [STRIKE]idiom[/STRIKE] phrase ''you never know'' but I want to know [STRIKE]particularly[/STRIKE] specifically [STRIKE]for[/STRIKE] if these sentences are correct.

[STRIKE]Where using *is* is correct.[/STRIKE] Is my use of "is" correct?

1) You never know which food is helping you [STRIKE]in controlling[/STRIKE] to control your weight.
2) You never know which good deed [STRIKE]is saving[/STRIKE] saved you.

See above.

I've corrected the capitalisation and grammar errors but they're not really natural uses of "You never know".

You never know when you might be hit by a bus so make the most of every day.
You never know when your relationship might end so enjoy every second of it.