Vegan children often fail to grow as well as their omnivorous cohorts despite protein intakes that exceed RDA. Explanations for inadequate growth include deficiencies of energy, calcium, zinc and vitamins B-12 and D. Due to decreased bioavailability, amino acids and nitrogen in vegan diets may be inadequate to support normal growth. Bioavailability of amino acids and nitrogen may be decreased by dietary fiber, food processing and storage, inadequate energy, and other unknown factors. Bioavailability should be considered when evaluating adequacy of intakes of protein, amino acids and nitrogen from vegan diets by infants and children.