Since your vet sells Science Diet in his office and makes money on the sales, I am willing to bet that he will give this food rave reviews.
Here is the list of ingredients from the large breed light food:
Corn meal, soybean mill run 16% (a source of fiber), chicken by-product meal (a source of natural chondroitin sulfate and glucosamine), peanut hulls, corn gluten meal, soybean meal, chicken liver flavor, vegetable oil, dried egg product, dried chicken cartilage (a source of natural chondroitin sulfate and glucosamine), flaxseed, L-lysine, taurine, L-tryptophan, L-carnitine, preserved with mixed tocopherols and citric acid, minerals (dicalcium phosphate, salt, potassium chloride, ferrous sulfate, zinc oxide, copper sulfate, manganous oxide, calcium iodate, sodium selenite), rosemary extract, beta-carotene, vitamins (choline chloride, vitamin A supplement, vitamin D3 supplement, vitamin E supplement, L-ascorbyl-2-polyphosphate (a source of vitamin C), niacin, thiamine mononitrate, calcium pantothenate, pyridoxine hydrochloride, riboflavin, folic acid, biotin, vitamin B12 supplement).
It gave your dog gas because your dog can not properly digest corn and soy. No dog can and yet they are the first two ingredients in the food. Chicken by products are the parts of chickens that they can't sell to anyone else.
Most vets have about a semester of dog nutrition classes. Your vet gets a big presentation from the pet food companies about how great their food is and then they sell it for a profit. In my opinion, not the best way to find out about how good a food really is.
My girls eat either a raw diet or Canidae. No soy, no corn. No gas.