Lufei is a rubber man, so his stomach can grow bigger and bigger like rubber, and he won't die if he eats too much. He has this talent, so he can eat a lot of food that ordinary people can't eat at one time. When he is in a hurry, he often puts a table full of food into his mouth, and his mouth bulges like a cannon and runs away.
If you don't give Luffy meat, Luffy's combat effectiveness will drop even more than others, because without meat, there is no strength, and without strength, you can't fight. Luffy thinks so.
Glacia is another supernova and a big eater. She doesn't have a rubber stomach, so everything she eats goes into her stomach. It's terrible.
Wu is usually greedy. He doesn't eat much, but he likes eating very much. If there is something delicious, he will definitely not let it go. So during the two years of practice, he has become a huge fat man. His movements are so difficult that he can't fight at all. In order to help Luffy and fight with Luffy two years later, he decided to lose weight.