
If your brother is *certain* that his dog has sufficiently relieved itself throughout the day and again before bedtime, then TBH I'd be pointing him towards the vet to have the dog checked over.
If he genuinely believes this behaviour is down to diet alone (which IMO would be odd!) then perhaps he should investigate making some gradual changes to see if it makes a difference, i.e. the timing / number / volume of each meal.
However, if this is a sudden behavioural change in the dog, then IMO the vet should be the first port of call.
regards, Teri :)