From the "Art and Science of Low Carbohydrate Living":

Current guidelines recommend 0.8 grams/day of protein per kilogram of body weight for adults, with more for children, adolescents, and pregnant women. Most people in the US get much more than this unless they are vegan or vegetarians or make really lousy food choices. So beyond this minimum, the key questions about protein are: 1) is the minimum recommended intake optimum; if not, how much is? And 2) how much is too much?

The question of defining an optimum protein dose does not have a simple answer. In addition to growth in childhood and pregnancy, multiple factors significantly alter your daily protein need. Important variables that increase an individual’s protein need include energy restriction (i.e., weight loss dieting), inflammation or illness, and recovery of lean tissue after a period of loss (such as following starvation, famine, or prolonged illness).

Another factor known to influences our body’s need for protein is the mix of carbohydrate and fat that provides most of the energy in our diet. However, the magnitude of this factor is very dependent on timing. In short term studies, taking away dietary carbohydrate and replacing it with fat reduces our body’s efficiency in using protein. Put another way, when you first take away dietary carbs, you need more protein to maintain muscle and other protein-containing tissues. But when you observe a human over a number of weeks of adaptation to a low carbohydrate diet, most of this initial inefficiency in protein use goes away[27]. Thus, once you are keto-adapted, your body’s need for protein isn’t much higher than during a ‘balanced diet’. This is a key fact in our understanding that low carbohydrate diets used in the long term do not need to be particularly high in protein.