Appropriate physiological functioning requires optimal nutrition, which needs to be in balance to prevent potential detrimental interactions, especially when administered at pharmacological dosages. Many nutrients function in harmony to complement digestive function and assimilation. Some may hinder these processes and compete for uptake, while others may also be required in tandem to assist in metabolism which may ultimately affect a number biochemical cycles. Many similar synergistic and antagonistic functions exist within human physiology and should be considered, particularly in the health and research arenas, where positive outcomes may be more likely if nutrient preparations are formulated with assistant supplementary nutrients, while nutrient related confounders need also to be accounted for. A variety of these are discussed in detail, with emphasis on relationships in health and disease.