The reason for high protein on a calorie restricted diet is satiation and the prevention of muscle loss.  When you calorie restrict, any food is weight loss food.  Even Twinkies.  Otherwise, the amount of protein you eat is linked to weight gain.  A 2012 study in the Journal of the American Medical Association found that although calories play a bigger role in weight gain, protein also plays a part. Researchers split healthy individuals into three groups and added 1,000 calories to their diets, but with varying degrees of protein. Those who ate the least amount of protein gained the least amount of weight, but they also lost muscle mass and stored more than 90 percent of extra calories as fat.  http://www.livescience.com/36899-protein-diet-weight-gain-atkins.html