pic from Westonaprice.org
I bet Lent is Very Much Not Fun for them.
Actually there is a thread about it.
Some compromises are hard to avoid but all in all it can be done
During fasting time two diets need to be balanced, Low Carb High Fat (LCHF) / Weston Price.. and the Fasting rules.
For LCHF you eliminate all sugar and wheat and most grains and vegetable oils and highly refined junk food..
For the fast you eliminate meat, dairy, fish except on occasion, olive oil except on occasion.
What is left: Vegetables, Sweet Potato's or White Potatoes, COFFEE, teas, fruit, coconut oil ( high in fat), fish oil supplements, and Lentin seafood like shrimp, mussels, squid,crab etc.
I have needed to add back in something like brown rice and I eat lots of Yams. I eat figs when I get hungry and if I need more I eat grits ( corn mush) or potentially Oatmeal but I havent needed to just yet.
Compromises should be things not sugar and not Wheat.. So if you need to fall back, rise or Oats is better.
That's plenty, especially if you use coconut oil generously as it gives you enough fat to burn. I make a tea with hot water and a large spoonful of coconut oil. It's greasy and gross but it keeps you from getting too hungry. I also give in to Margarine but I try to get the kind that they jack up with Omega 3's.