Although short - term randomized clinical trials have shown a beneficial effect of high protein intake, 3,4,20,21 the long - term health consequences of protein intake remain controversial.8,9,22 - 25 In a randomized clinical trial with a 2 - year intervention, 4 calorie - restricted diets with different
macronutrient compositions did not show a difference in the effects on weight loss or on improvement of lipid profiles and insulin levels.26 When protein is substituted for other
macronutrients, the
dietary source of protein appears to be a
critical determinant of the outcome.