Protein increases satiation and satiety more so than the other two macronutrients, carbs and fats.
so 是个“替代词”,它可以替代一个词语、一个成分或者一个词组,甚至一个句子的谓语部分。在本句,它应该是替代前文中的一个“程度副词”,修饰 increases,比如 greatly(这是一句话,more 前面不可以加逗号):
Protein increases satiation and satiety more greatly than the other two macronutrients, carbs and fats.