ReviewAddendum to “gluten-free and casein-free diets in treatment of autism spectrum disorders: A systematic review”
Introduction
Shortly after Research in Autism Spectrum Disorders published our literature review on gluten-free and casein-free (GFCF) diets in the treatment of autism spectrum disorders (ASD; Mulloy et al., 2010), a study by Whiteley et al. (2010) involving the experimental evaluation of a GFCF diet was published in Nutritional Neuroscience. Whiteley et al. concluded their data demonstrated that the GFCF diet had a positive effect on the developmental outcomes of some children with ASD. In their study, they implemented a strong research design that commendably included a combination of elements not present in previous studies of the GFCF diet (i.e., random assignment, long diet periods, and a blinded measure). Such elements are required to produce conclusive evidence (Schlosser, 2009, Simeonsson and Bailey, 1991, Smith, 1981). However, the study also presents a number of weaknesses (methodological and data concerns) that recommend caution in interpreting the results, limit the possibility of drawing definite conclusions, and do not currently allow one to reverse the general views expressed in our review.
From our review of the literature on GFCF diets in treatment of ASD, we noted that there were some studies that reported that the diet is efficacious and some that reported it is ineffective. All studies contained weaknesses that compromised their findings’ validity, although studies that reported that the diet was efficacious contained the most severe and numerous flaws. In our review, we concluded that the literature does not support use of GFCF diets in treatment of ASD in light of the methodological problems with these studies, including problems related to internal validity, measurement problems, construct validity, and plausible alternative explanations for study outcomes.
The Whiteley et al.’s (2010) study admirably protected against threats to internal validity, measurement problems, and construct validity with its strong research design. Even so, weaknesses regarding Bonferroni adjustments for statistical tests, systematic bias in the pattern of participant attrition, discrepant outcomes across comparable sub-domains of measures, and potential sources of measurement bias suggest the findings and conclusions of Whiteley and colleagues should be interpreted with caution.
Section snippets
Summary of the Whiteley et al. (2010) study
The purpose of the Whiteley et al. (2010) study was to experimentally evaluate a GFCF dietary intervention for children with ASD. To this end, the researchers enrolled 72 children diagnosed with ASDs, aged 4 years to 10 years 11 months, who did not have co-morbid diagnoses of epilepsy, fragile-X syndrome, tuberous sclerosis or a developmental age below 24 months. The participants were randomly assigned to a diet (n = 38) or no-diet group (n = 34). Participants in the diet group maintained a GFCF
Appraisal of the Whiteley et al. (2010) study
A first concern raised by the study pertains to Bonferroni adjustments to alpha levels for statistical tests. Whiteley et al. performed very large numbers of statistical tests during two rounds of analyses. In the first round, they applied a less stringent alpha adjustment than for which typical conventions would have called (Khattree & Naik, 1999). In the second round, they did not adjust the alpha levels and instead used the standard value of .05. Use of standard Bonferroni adjustments would
Summary
The weaknesses in the study by Whiteley and colleagues (2010) regarding data analysis, participant attrition, discrepancy across comparable measures, and potential bias in parent ratings suggest that their findings and conclusions should be interpreted with caution, as there are plausible alternative explanations. Consequently, we retain our position that GFCF diets are not effective treatments for the core symptoms of ASD (i.e., social and communication deficits, stereotypic/repetitive
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Cited by (21)
Anthropometric measures of Spanish children with autism spectrum disorder
2015, Research in Autism Spectrum DisordersCitation Excerpt :For instance, the National Research Council (2001) refers to GF/CF diets as a non-established treatment and a questionable intervention in children with ASD. Equally, comprehensive reviews of GFCF diets in children with ASD can be found in Mulloy et al. (2010), Mulloy et al. (2011) and Marí-Bauset, Zazpe, Marí, Llopis, and Morales (2014). As suggested in these reviews, the effectiveness of GF/CF diets has not yet been confirmed.
A review of declared factors identified by parents of children with autism spectrum disorders (ASD) in making intervention decisions
2013, Research in Autism Spectrum DisordersCitation Excerpt :In this case “research” seems to refer to the claims of efficacy of dietary interventions and vitamins, possibly accessed through non-technical publications or the Internet, or that the parents personally sought out information (and considered this research). Neither of these interventions has been reported to have clear empirical support in recent research reviews (Millward et al., 2008; Mulloy et al., 2010, 2011; Nye & Brice, 2005; Roberts & Prior, 2006). While there was evidence that at least some parents reported placing considerable weight on research when selecting interventions (Hanson et al., 2007; Le Grice & McMenamin, 2001; Loomis, 2007; Study 2 in Smith & Antolovich, 2000; Valentine, 2010), there is considerable evidence to indicate that many interventions used by parents are in fact not research-based (Bowker et al., 2011; Christon et al., 2010; Goin-Kochel et al., 2007; Green et al., 2006; Hanson et al., 2007).
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