The protein intake during the Palaeolithic period has been estimated to be two and a half fold greater than current recommendations. Hydrogen, nitrogen, oxygen and carbon atoms are important components of essential and nonessential amino acids which are components of proteins. These simple molecules play an important role in the human body. The 22 known amino acids, essential and nonessential, affect a broad range of physical and mental processes. Recent studies indicate that amino acids are cell signalling molecules as well as being regulators of gene expression and the protein phosphorylation cascade. The majority of the neurotransmitters is composed of amino acids and can influence biological functions related to brain-body interactions. Amino acids are key precursors for syntheses of hormones and low-molecular weight nitrogenous substances with each having enormous biological importance. Physiological concentrations of amino acids and their metabolites; nitric oxide, polyamines, glutathione, taurine, thyroid hormones, and serotonin are required for the biological functions in our body. These metabolites are known to be protective against cardiovascular diseases and degenerative diseases of the brain. However, increased concentrations of amino acids and their products (e.g., ammonia, homocysteine, and asymmetric dimethylarginine) are pathogenic factors for neurological disorders, oxidative stress and cardiovascular disease. Glutamate is a nonessential amino acid present in many foods that is considered protective against obesity and cardiovascular diseases. Therefore a balance between amino acids and other nutrients appears to be important for normal physiological functions without any adverse effects.