From Modern History TV:
https://www.youtube.com/watch?v=WeVcey0Ng-w “What Did Peasants Eat in Medieval Times?”
https://www.youtube.com/watch?v=i9RDaf8j2Yg “How Healthy Was Medieval Food?”
https://www.youtube.com/watch?v=Ertx8fZiuxA “What Did Rich Nobles Eat in Medieval Times?”
Reasonable guesses are one thing -- this research found hard data. The problem with reconstructing peasant diets has been, they were by and large illiterate, and their diets were of little importance to anyone besides the "fish only on Friday" popes. A unique example of centuries of records of minutiae is discussed in Wood's "Story of England", the village of Kibworth, Leicestershire became of interest to Oxford (probably due to a financial link):
BBC. Michael Woods. Story of England. 3 of 6. The Great Famine and the Black Death