With Nutrium, you can not only add your own food but also add dietary supplements and their nutritional value.
To create your supplements, you only need to go to "Foods" on the left-side menu, click on "Create dietary supplement", and fill out the nutritional information accordingly. To add a serving size/common measure your need to click on the section "Common measures".
To use dietary supplements on your client's meal plan you just need to choose the food composition database "My dietary supplements" when adding foods to a meal plan on the section "Meals".
This will allow your meal plans to be more complete and adapted to different situations.