The human body broadly requires three macronutrients and several micronutrients to function optimally. The three macronutrients it requires are proteins, fats, and carbohydrates. All three macros are essential for various biochemical processes of the body.
An ideal diet would consist of all three macros in all three meals. A protein-only diet is far from healthy and, in fact, can lead to adverse effects on health. Consumption of over 200gm of protein daily and lack of other macros can lead to protein poisoning. Protein poisoning is a serious condition that can lead to death.