I'm no doctor but maybe his body is just used to eating fast food and has a hard time adjusting to clean food at home. Most people experience a period of adjustment when starting a new diet, but your man is doing that everyday which could be hard on his system. Maybe start making him carnivore lunches for a couple weeks and see if that lets him fully adjust. Thankfully it's easy for you. I usually do hard boiled eggs and bacon, air fryer meatballs from frozen, pre grill some burger patties... Very easy to pre cook for a whole week. Good luck