How does a person get their protein?
Legumes: Beans, beans, and more beans.
Garbanzo beans a.k.a. chick peas are the primary ingredient of hummus, which can be combined with all sorts of veggies to make a wonderful dipping sauce for flatbreads (pitas)
Spineless seafood is permitted in all the fasts: Shrimp, scallops, mussels, clams...yes, even lobster (but pass on the melted butter).
Peanut butter, so long as it is light on the oil.
It is certainly “doable”. This will be my second Lent to be fully observant. Last year I lost about 8 pounds over the seven weeks.