Elimination Diets, Not Food Selectivity, Are Associated with Reduced Nutritional Status in Children with Autism Spectrum Disorder

Background/Objectives: Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication, restricted and repetitive behaviors, and sensory processing abnormalities, including food selectivity. Due to the lack of effective causal therapies, alternative approaches such as dietary interventions are increasingly being explored. This study aimed to assess the impact of dietary factors on the nutritional status of children with ASD. Methods: A total of 103 children (75 with ASD and 28 controls) were included. Nutritional status was assessed using biochemical markers and standardized anthropometric measurements. Associations between nutritional status and dietary factors, particularly elimination diets implemented either on medical indications or in the absence of clinical justification, were analyzed. Results: ASD diagnosis was independently associated with lower height SDS (Standard Deviation Score). Food selectivity was significantly associated with growth patterns: children with food selectivity showed a higher prevalence of short stature compared with the control group (15.2% vs. 0%, p = 0.033). Children following elimination diets had significantly lower BMI SDS compared with those without dietary restrictions (−0.35 [−1.29 to 0.05] vs. −0.22 [−0.78 to 1.14], p = 0.046), although only 11.1% had medical indications for such interventions. Among non-supplemented participants, vitamin D deficiency was significantly more prevalent in the ASD group (84.6% vs. 33.3%, p < 0.001). Conclusions: Elimination diets were the only dietary factor associated with a clinically relevant reduction in BMI SDS in children with ASD. Food selectivity alone was not associated with impaired nutritional status. Most elimination diets were implemented without confirmed medical indications. These findings highlight the importance of evidence-based dietary management and routine vitamin D supplementation in this population.