the comments about 'treats' are nonsense. Any real food that you give that they can choose to eat, or not, is fine, and probably healthier for them than ultra-processed commercial pellets, which include additives to facilitate the production process, preservatives to extend the shelf life, and more chemicals to improve the nutritional value and palatability for chickens who wouldn't otherwise touch the stuff.
You might find this interesting and useful
https://www.backyardchickens.com/ar...eat-tears-a-calculator-or-deep-pockets.78655/
My birds and their chicks eat what is there described and are healthy, lean, fit, and fecund. And 7 year old hens are still laying. And chicks get live mealworms and plenty of other things other posters have told you disrupt their growth. Edited to add, and they don't have diarrhoea, needless to say. It's nonsense. See e.g.
View attachment 3829189
This bird has never eaten any commercial feed.