If i could clarify...
"While protein serves as a building block to repair and maintain the integrity of your cells, tissues and organs and fat is involved in the production of hormones and is a constituent of the membrane of each of your cells, the main role of carbohydrates is to provide energy. Some of your body cells, especially in your brain and your red blood cells, prefer to run on glucose, a type of sugar that can be obtained through the consumption of carbohydrates. When you exercise, your muscles can also use glucose as their main source of fuel".
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Carbs are actually the energy for brain and central nervous system function, not protein.
Protein is in fact used to build muscle, tendons and ligamnets, through the amino acids.
Fats ARE a healthy and mandatory part of healthy body function.
Sounds like your son was running on Ketosis.. (atkins hybrid).. which is effective for short term weight loss, however cutting all carbs from a diet is a temporary solution with little known long term effects...
(i do nutrition)