How to send node as body content in email using Rules?
It depends on the Rules Event that your rules is using ... e.g.:


If Rules Event is something like "After updating existing content", then you'll be able to use token [node:body] within (eg) the message body of Rules action "send eMail".
If Rules Event is (eg) "After updating an existing user account" then token [node:body] is not available for using it within (eg) the message body of Rules action "send eMail".