Meal worms will make them fat! If you want to give them yummy treats that they will enjoy feed them things like salad ingredients and veggies (lettuce, bell peppers, cucumber, zucchini, tomato, broccoli, squash, cabbage (but NEVER feed potato, you can feed them sweet potato however),etc) and fruits (grape, apple, pear, banana, etc). They love these sorts of treats! Feed things like mealworms very occasionally, and spread them out through grass so that they have to work to get to them. They will scratch in the same spot for a long time! My chickens get bread, rice, and mealworms on only super special occasions (like their birthdays lol. I saw a thread on here where someone made their chickens a birthday cake!).