 Protein combining, protein combining or protein complementing is a dietary theory for protein nutrition that purports to optimize the biological value of protein intake. According to the theory, vegetarian and vegand diets may provide an insufficient amount of some essential amino acids, making protein combining with multiple foods necessary to obtain a complete protein. The terms complete and incomplete are outdated in relation to plant protein. The position of the Academy of Nutrition and Dietetics is that protein from a variety of plant foods eaten during the course of a day supplies enough of all essential amino acids when caloric requirements are met. The theory of protein combining has been discredited by major health organizations. Studies on essential amino acid contents in plant proteins have shown that vegetarians and vegans do not actually need to complement plant proteins in each meal to reach the desired level of essential amino acids as long as their diets are varied and caloric requirements are met. The American Dieteric Association and Dietitians of Canada support this position.