The aim of the study was to determine the level of nutrition knowledge and diet quality, understood in terms of healthy and unhealthy eating habits, among young people with orthorexic tendencies. The participants were school students, university students, and those employed in the Lublin region (N = 473). The data were collected by means of a questionnaire. The participants were asked to provide socio-demographic data through filling in the ORTO-15 questionnaire and the Dietary Habits and Nutrition Beliefs Questionnaire (KomPAN). The participants obtained results ranging from 9.3 to 100 (M = 31.15; SD = 11.81) in the non-healthy diet index, from 0.4 to 78.6 in the pro-healthy diet index (M = 21.79; SD = 11.08), and from 0 to 23 in the domain of nutrition knowledge (M = 13; SD = 4.23). A variance analysis showed no significant differences between the pro-healthy diet index and the level of nutrition knowledge. The group with orthorexia obtained statistically higher results in the pro-healthy diet index. Those with a tendency toward orthorexia obtained statistically higher results in the non-healthy diet index. The variance analysis showed that the level of nutrition knowledge of those not focused on healthy foods was significantly lower than in the other groups. The results of the ORTO-15 questionnaire correlated negatively with the pro-healthy diet index and the level of nutrition knowledge, and positively with the non-healthy diet index. We concluded that: 1. the orthorexic group and the group with a tendency toward orthorexia could be characterized with a moderate intensity of a healthy diet and a low intensity of a non-healthy diet; and 2. the level of nutrition knowledge in the orthorexic group did not significantly differ from that of the other groups.
Keywords: diet quality; nutrition knowledge; orthorexia.