Luffy is like the ancient weapon used by Imu, he cannot fight in a long duration without eternal supply of food.
What is energy?
There used to have two sources of energy, fire and electricity. That is what people commonly use to power up any kind of constructs.
Oddly, We didn't know how Franky can use beverages to power himself.
But now Lilith introduced the ODC (Omni-Drain Converter) which can converts any source of energy into a different energy. She converts the energy into beverages. I think to myself, this is complete nonsense. I think a little more and realize human's intestines can absorbs the minerals inside the food and converts them into nutrient molecules. So the foods or beverages are technically energy sources for any living being. Since Lilith demonstrate ODC can converts energy into beverages, that means there is a way to converts them into food too. So Luffy can just swallow "The Sun" in the mural and the ODC to have an eternal food source.
Suddenly I think of something, what if the One Piece is an eternal food machine, it's useless for everyone but not for Nika. That will be very ridiculous.