First seen BrinkZone, the original study can be found on JAMA : Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating.
In summary, weight gain when eating a low protein diet (5% of energy from protein) was blunted compared with weight gain when eating a normal protein diet (15% of energy from protein) with the same number of extra calories. Calories alone, however, contributed to the increase in body fat. In contrast, protein contributed to the changes in energy expenditure and lean body mass, but not to the increase in body fat.