my very skinny lab

Question
I have a 2 year old black neutered lab.  We got him a year ago from east riding lab rescue and think he was not badly treated but did not recieve much love and attention.
He is really thin we can see his ribs and we've been feeding him 400g of dry food per day ( plus little extras!).
He is also very very active in fact hyperactive!
We also own a choc lab (not spayed) and we feed her half the ammount but shes overweight!
Our main concern though is getting some more weight on Jake the black lab as he looks so thin.  He 'll eat absolutely anything and steal anything he can get his paws on too.
What do you suggest.
Thanks

Answer
If you haven't had the vet check him for worms or other problems, do so.  Otherwise go ahead and feed him whatever it takes.  We once found we had to feed an active, under weight Lab more like 700 grams a day before she really started gaining weight.  Another one, we had to feed 600 grams to maintain a lean build on him.  Both dogs were eating Pro Plan, a concentrated, meat based chow that many labs do fine on 300-400 grams.  

You really need to get both them to their ideal body condition.  Your dog definitely should be narrower at the waist than the hips and chest. You should be able to easily feel the ribs, but not see them.  Each dog is different.  Standard recommendations are a good place to start, but each dog must have its food and exercise adjusted to its individual needs. Here is a link to a good illustrated guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx