RESUMEN
(1) Background: The literature regarding orthorexia nervosa (ON) has well documented the association with other mental disorders, such as obsessive-compulsive and eating disorders. However, the research has not taken into account stress-related behavior and the conduction of physical activity (PA), both structured and unstructured. (2) Methods: In this cross-sectional study, 165 students of the University of Parma (92 females and 74 males) aged between 18 and 49 years old (mean = 24.62 ± 4.81) were consecutively recruited. The ORTO-15 questionnaire was used to divide the total sample into a group without orthorexia (score > 40) and a group with orthorexia (score < 40). All subjects completed the P Stress Questionnaire, and specific items were extrapolated from the Eating Habits Structured Interview (EHSI) to investigate lifestyle, including structured and unstructured PA. (3) Results: Subjects with orthorexia represented 83% of the total sample and reported higher levels of stress-related risk behaviors (i.e., sense of responsibility (t = -1.99, p = 0.02), precision (t = -1.99, p = 0.03), stress disorders (t = -1.38, p = 0.05), reduced spare time (t = -1.97, p = 0.03), and hyperactivity (t = -1.68, p = 0.04)) and a higher frequency of PA (i.e., hours spent training in structured PA, daily (t = -1.68, p = 0.05), weekly (t = -1.91, p = 0.03), and monthly (t = -1.91, p = 0.03), the tendency to carry out physical exercise even if tired (t = -1.97, p = 0.02), and to adhere to unstructured PA (i.e., moving on foot or by bike rather than using transport (t = 1.27, p = 0.04)). (4) Conclusions: The results confirmed the presence of hyperactivity at a motor and behavioral level in people with orthorexia. Further studies are necessary to highlight the causality between ON, stress, and physical activity but it may be possible to hypothesize that "obsessive" physical exercise may not generate the benefits generally known by the literature.