I really think you are missing the point. Don't fast just to follow rules that you don't even understand (if you don't understand them then you really aren't truely using 100% of your spirituality when you blindly follow rules). Instead, fast to follow your faith. Jesus fasted for 40 days to prepare for his ministry. Catholics fast during Lent to (1) help imitate the example of Jesus, (2) display common repentance, and (3) help you put aside your earthly passions and instead think of God and Jesus for a day. The 'rules' for Catholics vary from country to country and even vary over the years. Some Catholic regions avoid food altogether, some allow one meal per day, some avoid any meats, some avoid any non-seafood meat, some just avoid red meat, etc. So don't do anything just to follow arbitrary rules, instead do it for the three reasons I listed above. Would eating chicken stock prevent you from doing those three things? The answer will vary from person to person.