You can make a bread using braken flour. Is toxic at long term, but canker is not a problem if you are in a hurry and do not plan to live more than 50 years in any case. Probably they would combine Triticum and Pteridium together making a more palatable product.

Many things could point to stolen food and a harsh conditions. He was probably desperate for food. For a human eating fat regularly, he was very slim.