This is a discussion topic for the Ore project, FixedFoodBar. View the full project on Ore for downloads and more information.
This uses a hacky way to prevent food from changing in sponge. This is a simple lightweight plugin as of request of Need help finding a good plugin - #6 by MoseMister
You can set the food value to a fixed number or link it with another value of the player such as the players health.
/ffb config value <value>
Sets the value/link of the food level for all players
Allows the use of the only command