Eating disorders represent a complex and multifaceted public health challenge, highly prevalent among young people. Background and Objectives: To examine the prevalence of eating disorders in the Spanish young adult population aged 18–30 years, and their correlation with various eating habits and lifestyle factors. Materials and Methods: A descriptive, cross-sectional survey was carried out using a non-probabilistic snowball sample. The valid and reliable NutSo-HH Scale was employed to collect data on nutrition, lifestyle, and health habits. Results: Data were collected from 9692 Spanish young adults, of which 101 (1.04%) were diagnosed with anorexia nervosa and 71 (0.73%) with bulimia nervosa. The prevalence of anorexia and bulimia was significantly higher (p < 0.001) in women than in men, regardless of socio-demographic variables such as educational level, income, region, and size of city of residence. A considerable percentage of participants showed possible symptoms of eating disorders. Nutritionally, individuals with eating disorders consumed less fast food and fried or ultra-processed food but tended to consume coffee and energy drinks more frequently. Additionally, sleep quality and duration were more adversely affected in individuals with eating disorders compared to the general population. Sedentary lifestyles did not significantly differ between those with eating disorders and healthy individuals, though physical activity increased in people with bulimia. Conclusions: The interplay between young adults’ dietary habits, lifestyle factors, and mental health underscores the urgent need for targeted interventions to effectively address these complex public health challenges.