How to load part of a big structure to the workspace?

I have a big structure and loading it would take a long time. I need a specific variable in that structure. Is there any way I can do it faster. Suppose my structure is A. I need a field with the index i, that is I need to access to A(i).B.C.F

Answer 1

[Stephen23]

Use matfile, that is exactly what it was designed for.

[MINA]

I used matfile but still it's very slow.

[Stephen23]

If that is still very slow then it might be slowed down by being uncompressed. Perhaps one of the .mat file experts might like to comment on this?