What is the recommended amount of dietary protein for adult humans?
Low-protein diet
The daily requirement for humans to remain in nitrogen balance is relatively small. The median human adult requirement for good quality protein is approximately 0.65 gram per kilogram body weight per day and the 97.5 percentile is 0.83 grams per kilogram body weight per day.[7] Children require more protein, depending on the growth phase. A 70kg adult human who was in the middle of the range would require approximately 45 grams of protein per day to be in nitrogen balance. This would represent less than 10% of kilocalories in a notional 2,200 kilocalorie ration. William Cumming Rose and his team studied the essential amino acids, helping to define minimum amounts needed for normal health. For adults, the recommended minimum amounts of each essential amino acid varies from 4 to 39 milligrams per kilogram of body weight per day. To be of good quality, protein only needs to come from a wide variety of foods; there is neither a need to mix animal and plant food together nor a need to complement specific plant foods, such as rice and beans.[8] The notion that such specific combinations of plant protein need to be made to give good quality protein stems from the book Diet for a Small Planet. Plant protein is often described as incomplete, suggesting that they lack one or more of the essential amino acids. Apart from rare examples, such as Taro,[8][9] each plant provides an amount of all the essential amino acids. However, the relative abundance of the essential amino acids is more variable in plants than that found in animals, which tend to be very similar in essential amino acid abundance, and this has led to the misconception that plant proteins are deficient in some way.
Sport dog nutrition
Protein is an essential component in any dog's diet.  Muscle, hair, skin, ligaments, cartilage, and chest and abdomen organs are structurally supported by protein. In comparison to the average dog, a performance or sporting dog requires a greater protein intake. This is a result of wear and tear on muscles and other organ tissues caused by strenuous activity. Protein is also a vital component in bodily functions such as transporting oxygen and energy to the muscles, regulating blood glucose levels, fighting infections, and repairing tissues. Many diets targeted for performance dogs contain 30% protein. However, dogs performing in different athletic activities can require varying amounts of protein and essential amino acids. For instance, studies have shown that sled dogs require a high protein, high fat diet, where 30 to 40% of energy comes from protein and 50% of energy comes from fat. Greyhounds were found to require a moderate protein (25% energy) and moderately high fat (30-50% energy) diet. At present there are conflicting opinions concerning whether protein from animal sources is of higher quality than protein from non animal sources. For instance, a study completed by Brown et al., concluded that "In a 16-week controlled experiment, a meat-free diet maintained haematological characteristics in sprint-racing sled dogs (Siberian huskies)". No deficiencies or side effects were noted in this study. However, in previous studies it was discovered that when feeding non animal protein diets to performance dogs, a larger prevalence of anemia was found in comparison to when dogs were fed diets containing animal protein. Poor iron bioavailability can lead to anemia. As stated by Chausow and Czarnecki-Maulden, it is generally accepted that animal sources of protein have more iron bioavailability than plant sources. Studies have been conducted to compare iron bioavailability when feeding animal and non animal sources of protein. However, research on dogs for this topic is are lacking. Studies completed by Chausow and Czarnecki-Maulden conclude that more research needs to be done on iron bioavailability of plant and animal protein sources. Regardless of the source, when feeding the sporting dog, protein is an essential component of the diet. Nutritional demands must be met in order to achieve high performance levels.