In the wild, dogs eat what other animals they can kill, or scavenge from the carcases left by other carnivores. They also eat wild fruit. It follows that pet dogs have digestives systems designed to eat the same things. So what is the best diet for an adult dog? Obviously, one which is near to its natural diet. BARF is the common term - it stands for ‘bones and raw food’ or ‘biologically appropriate food’. Apparently chicken provides the best balanced source of nutrients. Ideal are raw chicken wings and carcases (the remains of the chicken after the wings, drumstick and breasts have been removed for human consumption). It must be emphasised that these must be RAW as dogs happily digest raw chicken bones - but when cooked these bones become brittle and break into very sharp pieces which penetrate guts and kill the dog! Raw fruit of all kinds is good, if it is good for you it is good for the dog - which will always be eager to share whatever fruit you are eating. Vegetables are a different matter, their cell walls cannot be digested by dogs so they need to be broken down by cooking so the nutrients within are made accessible. In wild dogs the vegetable equivalent in the diet is provided by eating herbivores’ guts and their part-digested contents.
Most vets will tell you that a BARF diet is totally unsuitable for your dog (especially if they are selling expensive artificial dog foods). How would they know? Most vet courses have far too few lectures on canine nutrition - and these are usually given by (possibly biased) experts employed by the pet food manufacturers!
Along with the chicken wings etc. you may like to give a little very plain dog biscuit, or stale wholemeal bread. For treats, avoid highly coloured dog biscuits as the chemical colourants can have adverse affects (just as some foods can affect hyperactive children).
A traditional alternative is to feed tripe and plain biscuit etc. Tripe is the unwashed stomachs (rumens) of cattle (or sheep or goats) usually fed raw and minced. It can be purchased from many pet shops, deep frozen and cut into blocks (typically about 1lb each). Having been deep frozen there is no risk of parasitic worms. The dogs like tripe, but many owners don’t - because it is so smelly, and some people don’t like putting it in their deep freezers with their own food, no matter how carefully wrapped it is.
This is a large subject, explore it by reading. Two suitable books are ‘Give your dog a bone’ by Ian Billinghurst (who has now written several other books on this topic), and ‘Natural nutrition for dogs and cats’ by Kymythy Schultze. A useful web site is http://www.willowglen.com/barf.htm