What is a good pattern to keep changes to a hierarchical object persisted?

Consider that we have a similar object hierachy as illustrated below where a User has a group of Profiles and each profile a group of Settings.

class User {
   private final List<Profile> profiles;
}

class Profile {
   private final List<String> settings;
}

What is a good way ensure that any changes to the above objects are also persisted to disk? The assumption is that a Profile can be big and I want to avoid persisting the entire User for a modification in a Profile.

Note that it's a design issue, not an issue about selecting the right object serialization library.