Protein (fish, poultry, eggs, meat) is the basic building block of your body and a major component of almost every system from muscle, to hormones, to digestive juices, to skin and hair… and much more.
Diets rich in carbohydrate (for example, pasta, rice, bread, desserts, etc). are often “enjoyed” at the expense of containing too little protein. Since your body needs protein daily, if you don’t consume enough, your body “steals” protein from the systems mentioned above. Essentially, you cannibalize yourself to get the building blocks you need. And body functions start to deteriorate. This breakdown and dysfunction are partially caused by a moderately addictive, non-essential macronutrient… carbohydrate.
If you have to choose only one of the 3 macronutrients (fat, protein or non-essential carbohydrate), choose protein because it enables your body to manufacture the other two.