Studies have shown that adults' comprehension of medical and nutrition terminology is often poor. This study's objectives were to determine nutrition terms that adults could not define correctly; to determine whether demographic characteristics affected the subjects' score, and to determine whether defining nutrition terms in educational material increased subject comprehension of the terms. Phase I involved 400 adult subjects from the airport and train station who were approached randomly and asked to complete a terminology test. Phase II involved 100 soldiers (aged 18–28) and 100 senior citizens; half of the subjects read information in which the nutrition terms used were defined and the other half read information in which the nutrition terms were not defined. All subjects then completed a nutrition terminology test. Statistical analysis included mean score, item analysis and regression analysis. In phase I, subjects had a moderate knowledge of the terms tested. In phase II, the mean score of subjects who read information in which the nutrition terms were defined was significantly higher than those not provided with definitions. The results of this study suggest that adult comprehension of nutrition terms may improve when the terms are define