that, those

[jinkmidh]

Somebody says
you cannot use "double those of" , so I have to use 'that' after the word 'double', 'triple'. Is this right grammar?

Here is the sentence.

"Researchers found that women who dined with two of three friends ate 700 calories on average, double that of solo diners."

In this sentence, if I use 'those' instead of 'that', it seems strange. I know that.
But is it because of the word double or
is there another reason?

Will somebody explain it?

[Bennevis]

"that" is the amount.

Researchers found that women who dined with two of three friends ate 700 calories on average - twice as much as solo diners.

Researchers found that women who dined with two of three friends ate 700 calories on average (while solo diners ate 350 calories on average).

Researchers found that women who dined with two of three friends ate 700 calories on average - double the amount solo diners consumed.

[jinkmidh]

Thank you for replying my question