This question comes from The Oxford Dictionary

[chimsm]

Hello Teachers and fellows.

When I looked up the meaning of "Frugal" on my Oxford dictionary, it shows the following.
"1. Using only as much food or money as is necessary"

The thing made me confused is the linking verb "tobe" in red color.
Could you please explain why it stands there and which grammatical structure is applied.
Personally, I always write " ....as much food or money as necessary" instead.

Thank you.

[Soup]

Hello chimsm

This is an example of ellipsis--the verb is omitted:

• Using only as much food or money as [is] necessary.

• ... as is necessary
• ... as necessary.