Background: Autism spectrum disorder (ASD) constitutes a heterogeneous neurodevelopmental condition frequently accompanied by considerable disturbances in feeding behavior and nutritional balance. These difficulties arise from complex and multifactorial mechanisms, exerting a significant impact on physical health, metabolic homeostasis, and psychosocial functioning. The present review aims to provide a critical synthesis of current evidence regarding the underlying biological and behavioral mechanisms of feeding difficulties in ASD and to delineate the spectrum of comorbid eating disorders within this population. Methods: A narrative review of the peer-reviewed scientific literature was undertaken, emphasizing studies investigating the interrelationship between ASD and nutritional functioning in pediatric and adolescent populations. Particular focus was placed on research exploring sensory processing abnormalities, gut microbiota alterations, and the clinical manifestation of eating disorders in individuals with ASD. Results: The analysis revealed that sensory hypersensitivity, behavioral inflexibility, and disturbances within the gut–brain axis constitute principal determinants of atypical eating patterns in ASD. Individuals on the autism spectrum frequently exhibit pronounced food selectivity, neophobia, and symptoms consistent with Avoidant/Restrictive Food Intake Disorder (ARFID). Furthermore, an increased prevalence of anorexia nervosa and orthorexia nervosa has been documented, likely reflecting shared cognitive and behavioral features with ASD. “Emotional eating” tendencies and a marked preference for high-caloric, energy-dense foods—often potentiated by psychopharmacological treatment and reduced physical activity—further contribute to an elevated risk of overweight and obesity. Conclusions: Children and adolescents with ASD display a bimodal distribution of body mass, encompassing both undernutrition and obesity, indicative of a multifaceted interplay among sensory, behavioral, cognitive, and metabolic determinants. A comprehensive understanding of this heterogeneity is crucial for the development of individualized, evidence-based interventions integrating nutritional management with behavioral and psychotherapeutic approaches.