A somewhat related discussion was here:
openmensa/openmensa#34

I was thinking on how to make the nutrition data available to me, so I can use it for my nutrition tracking. Currently I need to check the website instead of using the OpenMensa App, I use otherwise. Although providing nutrition data in a structured way would be the most elegant solution in my opinion, I think it should be easier to provide them via the notes field, as long as there is no structured way defined in the OpenMensa API.