proper weight and feeding

Question
hello jen,i have a 16 month old mostly lab freind that i rescued from the s.p.c.a,recently my roomate(who claims intimate knowledge of dogs as he was a horse trainer???)and several folks that hang out have started accusing me of neglegting my dog because they feel he is under weight.i am an a.b.k.a certified pct,as well as red cross certified so i hope my stead fastness on this subject is right especially for my dogs sake..i feed him 2cups of food twice a day .at 7 am,and again at 7 pm.is this sufficient??folks say because he will still eat that he is hungry and needs more food,i rebut that labs dont really have an off switch for food and will eat until they die,this is met with disbelief. i have also been told that since you can see the suggestion of his last rib (which i thought was something that the akc considered a breed standard???)that again he is unhealthy.is my best bud barney as unhealthy as they say??? or does he just love food,in his bowl on the floor,the trash can the sink ,,insert location here..please gimme a final word to either change my pattern of behavior or to shut my non dog owning roomies up  thank you

Answer
How much you feed is completely dependent on the dog's activity level and the quality of food.  Typically 4 cups spread out between 2 meals is enough for an adult dog.  

They should have a waist when you look down, and when you run your hands over their ribs, you should be able to feel them, but not so much that you can easily feel EACH rib.  You should NOT be able to see any bones on the dog when they are standing.  

Another good check is to have the vet look the dog over.  Vets tend to prefer thinner labs, but they will tell you if the dog is TOO thin.