Going up to 4.4 grams of protein per kg of bodyweight per day
https://jissn.biomedcentral.com/articles/10.1186/1550-2783-11-19
*****After a treatment period of eight weeks, fat mass increased in all three groups equally (~3.5 kg); however, lean body mass decreased by 0.7 kg in the low protein group in contrast to a gain in the normal (2.9 kg) and high protein (3.2 kg) group. According to the investigators, calories alone contributed to the increase in fat mass; however, protein contributed to gains in lean body mass but not fat mass [11]. Thus, eating extra calories will result in a gain in body fat; however, overfeeding on protein will also result in a gain in lean body mass perhaps due to an increase in muscle protein synthesis.
*****(does this sound familiar? Ive been throwing this at the bodybuilding community since the 90's)
One might suggest that the high thermic effect of protein may make it difficult to gain body weight during times of overfeeding. It has been shown that the greater the protein content of a meal, the higher the thermic effect [34]. Both young and old individuals experience an increase in resting energy expenditure after a 60 gram protein meal (17-21% increase)
*****Another factor that may have played a role in the current investigation is the type of protein consumed in the high protein group. Because of the difficulty in consuming 4.4 grams of protein per kg body weight daily, every subject in the high protein group acquired their additional protein calories primarily from whey protein powder. It has been shown that the thermic effect is greater with whey versus casein or soy protein [39]. Recently scientists demonstrated that consuming similar calories and protein during resistance training in initially untrained individuals resulted in greater gains in lean body mass in the whey supplemented group versus soy or carbohydrate [40]. Another investigation found that muscle protein synthesis after whey consumption was approximately 93% greater than casein and approximately 18% greater than soy. Furthermore, the same pattern held when measured post-exercise (whey > soy > casein) [41]. On the other hand, 48 grams of both whey and rice protein isolate consumed post resistance exercise improved indices of body composition and exercise performance similarly [42]. Thus, one might speculate that if the protein dose or intake is sufficiently high, it may not matter what that particular protein source may be.