The most likely cause for hip dysplasia is a random gene expressing the trait, or bad breeding practices. The misconception came from an American study performed in the '60s that claimed a relationship between high caloric intake and hip dysplasia. A subsequent Swedish study in the '70s found that the American study was flawed. Three more studies since then have found no link between caloric intake and dysplasia. One of these studies went so far as to induce premature births and a 50% restriction diet, and still found no reduction in the percentage of mature dogs with hip dysplasia. It's probably safe to say that there are not any wolves that say, "Okay Junior, you better watch your protein intake so that you don't develop hip dysplasia!" If there is a dietary cause to growth problems, it is more likely that pet foods that do not supply enough of the building blocks and nutrients required by a growing animal.
A breeder of Irish Wolfhounds and longtime customer of our diets says Timberwolf is the ONLY food he has ever fed where he had NO incidents of the growth disease Pano. There are only three sources of calories: protein, fat and carbohydrates. If you limit protein and fat, then more carbohydrates supply calories instead. However, carbohydrates only supply energy (calories - growth) but no nutrients. The reason most dog food companies push low protein foods is because they are much cheaper to make.
Foods labeled and marketed as senior or lite formulas are the cheapest to manufacture, and yet command a higher price and a higher profit margin attributed to their reputation in the consumer's mind. AAFCO guidelines for a puppy/nursing food dictate a minimum of 22% protein. This comes from research performed by the National Research Council that involved the use of beagles and purified amino acids. If the minimum required for puppies and nursing mothers is 22%, it should be prudent to use a somewhat higher percentage, just in case. If a dog does not receive enough protein in its diet, or if fat levels are high in relation to the level of protein, then the canine's system will go into a negative nitrogen balance in a short time. The higher the fat content of a food, the higher the level of protein is required.
Another issue to be taken into consideration is that most protein sources are not as digestible as purified amino acids, and there are a lot of breeds that have higher protein requirements than beagles. Dogs that are stressed (which includes most dogs) or debilitated have higher protein requirements also. Incidentally, and noteworthy, there is no AAFCO or NRC maximum level for the percentage of protein for canines. If feeding dogs high protein foods, one would think that there would be a maximum allowed level.
One of the first things your dog does after eating is to drink water. Because water is heavier than dog food, it may consume an equal amount of water by weight, thereby diluting the protein/fat percentages of the dog food.