From your 'My Hub' page (please see below)
On the left hand side of your account, you will see the side menu in which you can select 'Nutrition'.
You can then select 'Custom Food/Drinks' from the 4 options at the top of your page
Followed by 'Create Item' at the bottom of your page
You will then be able to add all the nutrient information for that product and save it to your database.