In pretty dang experiences individuals (Participants were otherwise healthy resistance-trained men and women who had been resistance training regularly for the last 8.9 ± 6.7 years and an average of 8.5 ± 3.3 hours per week.), the best study showing that the extra protein didn't add to body fat:
1. Antonio J, Peacock C, Ellerbroek A, Fromhoff B, Silver T. The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals. Journal of the International Society of Sports Nutrition. 2014;11(1):19.
BACKGROUND:The consumption of dietary protein is important for resistance-trained individuals. It has been posited that intakes of 1.4 to 2.0 g/kg/day are needed for physically active individuals. Thus, the purpose of this investigation was to determine the effects of a very high protein diet (4.4 g/kg/d) on body composition in resistance-trained men and women.METHODS:Thirty healthy resistance-trained individuals participated in this study (mean +/- SD; age: 24.1 +/- 5.6 yr; height: 171.4 +/- 8.8 cm; weight: 73.3 +/- 11.5 kg). Subjects were randomly assigned to one of the following groups: Control (CON) or high protein (HP). The CON group was instructed to maintain the same training and dietary habits over the course of the 8 week study. The HP group was instructed to consume 4.4 grams of protein per kg body weight daily. They were also instructed to maintain the same training and dietary habits (e.g. maintain the same fat and carbohydrate intake). Body composition (Bod Pod(R)), training volume (i.e. volume load), and food intake were determined at baseline and over the 8 week treatment period.RESULTS:The HP group consumed significantly more protein and calories pre vs post (p < 0.05). Furthermore, the HP group consumed significantly more protein and calories than the CON (p < 0.05). The HP group consumed on average 307 +/- 69 grams of protein compared to 138 +/- 42 in the CON. When expressed per unit body weight, the HP group consumed 4.4 +/- 0.8 g/kg/d of protein versus 1.8 +/- 0.4 g/kg/d in the CON. There were no changes in training volume for either group. Moreover, there were no significant changes over time or between groups for body weight, fat mass, fat free mass, or percent body fat.CONCLUSIONS:Consuming 5.5 times the recommended daily allowance of protein has no effect on body composition in resistance-trained individuals who otherwise maintain the same training regimen. This is the first interventional study to demonstrate that consuming a hypercaloric high protein diet does not result in an increase in body fat.
So, the extra protein didn't aid in either fat gains OR muscle gains, in these subjects, at least not statistically.
On average, the HP gained 1.9 vs. 1.3kg FFM, with -0.2kg and +0.3kg being the changes in Fat mass over the study...
Not statically significant (any of those variables), but given long enough time, it looks like both groups were gaining slowly and possibly some advantage to the HP vs. control group (without body fat being a negative side effect of gaining more FFM).
These guys were not big eaters, though. Both groups took in about 2100kcal / day at the start, but the HP group was averaging ~2800kcal / day by the end of the diet, with the change coming mainly from protein.
Bottom line is you can go pretty dang high in protein, using it as your main way to add kcal, and still not have fat gains as a major concern. This study doesn't answer the question as to what happens when / if someone takes in higher amounts of protein (e..g, this amount) and adds additional kcal from other macros on top if it, which would likely mean more body fat (which, given these data, we'd attribute to those other macros, not the protein).
-S