this idea that losing weight or gaining weight is simply a matter of calories in/ calories out and that the source of those calories doesnt matter is complete bs.
there is plenty of research out there showing A CALORIE IS NOT A CALORIE.
proteins, carbs, and fats all have very different effects on the metabolism, such as effect on homrome levels (insulin spike, glucagon, ect)...source of the calorie will also effect hunger n appetite, thermic effects, ect, ect, ect.
eating 300 cals or ben n jerrys/krispy kreme dounuts is goin to yeild a very different effect then eating 300 cals of baked chicken breast with veggies.
there are plenty of studies out there showing that diets with different macronutrient ratios but the same caloric intake have produced different results in a persons body composition.
this nonsense goes along with the idea that protein is protein...its just complete bs.