Conclusions
So, while we do biochemically possess the pathways needed to convert amino acids to fatty acids, the chances of that ever happening to a significant degree during higher protein intakes, even in the face of adequate energy and carbohydrates, are irrelevant given what we know about the extreme measures that need to be surpassed in order for any appreciable fat gain from protein to take place.
Indeed, overeating by ~1,000kcals/day for 8 weeks in combination with higher protein intakes did not amount to any additional gains in body fat compared to a lower protein, hypercaloric diet. Rather, excess protein in the face of overfeeding actually contributed to gains in lean body mass (be that what it may); quite the contrary to what textbooks and classrooms teach. In reality, the chances that excess protein contributes to body fat stores are insignificant, and arguably physically impossible under normal and/or reasonable hypercaloric conditions that most people/athletes might face on a daily basis. Only until theoretical extremes, either for protein intakes or calories or both are achieved, will there be any significant contributions to body fat from excess protein intake. This shouldn’t concern most people in the slightest.