Three good reads to start:

1. Primer on ultra processed foods: https://www.health.harvard.edu/blog/what-are-ultra-processed...

2. NOVA “the food classification that categorises foods according to the extent and purpose of food processing, rather than in terms of nutrients” [PDF]: http://archive.wphna.org/wp-content/uploads/2016/01/WN-2016-...

3. ‘Ultra-processed foods and added sugars in the US diet: evidence from a nationally representative cross-sectional study’: https://bmjopen.bmj.com/content/6/3/e009892