You can subscribe to a whole forum from the main thread list page ..
like for the whole weight loss forum
you would start on the main page of it and go to the right corner above the stickys and there is Forum Tools click that and select Subscribe to this forum.

then anytime any posts are made you get notified.

you can go to your User CP - Edit Options -and set the email notice time frame.
In the second section you will see this-

[ Messaging & Notification


Default Thread Subscription Mode

When you post a new thread, or reply to a topic, you can choose to automatically add that thread to your list of subscribed threads, with the option to receive email notification of new replies to that thread.
Default Thread Subscription Mode:] a drop down listing of choices will show here

*
you make your choice and be sure to click Save Changes at the bottom of the page