Pursuit of knowledge and scientific truth since Leonardo Da Vinci and the Renaissance, most especially during the past century, has revealed the human body as a miraculous machine. Our composition and physical functioning aligns consistently with our brethren in the animal kingdom. True to our origin, in health, over half our body is salt water.
The functioning parts, including our skeletal support, the heart that pumps our blood, the vessels carrying our blood, the gastrointestinal tract through which our nutrition enters, and the muscles that move us, that breathe the air, that control movements of our every part, are protein. Every body function is protein dependent, and the human body has millions of different protein molecules. Hemoglobin that carries oxygen in your blood, collagen that provides strength to bones and skin, keratin that provides a water-tight seal for the skin, and actin-myosin, the contractile units of muscle, are all proteins. Antibodies are immune proteins that help protect us against bacteria, viruses, and other micro-organisms. Functioning of our brain and nervous system involves many specialized proteins.
Dietary protein therefore, is essential to our existence. In an effort to lose weight and improve physical fitness, protein intake should not be significantly reduced. While increasing protein intake above and beyond what your body needs will not improve fitness, reducing protein intake below critical levels leads to malnutrition more quickly than reducing intake of the two other macro-nutrients, carbohydrates and fats.