Response to ‘Obesogenic’ oversimplification

Dear Editor, We read with interest the letter by Versace and Schembre titled ‘Obesogenic’ oversimplification (1), which addressed our recent systematic evaluation of attentional biases to food cues in overweight and obese individuals. We thank the authors for their interest in our paper and agree with certain points raised, particularly those emphasizing the complexity, heterogeneity and multifaceted aetiology of obesity. This is an integral assumption of research in this field and one that is stressed at numerous points throughout our systematic review. There are a number of concerns with Versace and Schembre’s perspective that we raise here. First, we disagree with the argument made that we, or other researchers contributing to literature in this field, may have been tempted ‘to overstate debatably unsubstantiated conclusions regarding group differences in attentional bias’. Our systematic review retrieved and presented 19 studies, which were published prior to November 2014 and systematized by cognitive task. Each of these studies included direct comparison of obese and healthy-weight persons’ responses to food and control stimuli and had undergone peer review as part of the submission process to high-quality journals. Second, we feel that it is incongruous for Versace and Schembre to imply that our systematic review contains ‘broad sweeping conclusions’ and yet refer to their single cross-sectional study, which is yet to be published, in order to support their conclusion. This undermines the systematic approach of a systematic literature review where the fundamental purpose is to critically evaluate the published literature holistically rather than at the individual study level. It is, indeed, unfortunate that the data presented by Versace and Schembre were not published prior to conducting our systematic literature search, as it appears that their unique experimental design could have made a valued contribution. However, without being able to read the paper in full, it is difficult to assess the quality of their data. Our systematic review featured four studies (2–5) that also reported no dissociable response pattern between obese and healthy-weight individuals; these findings reinforce our view that heterogeneity of results may arise through methodological variations and differences in cognitive task demands. Third, in contrast to Versace and Schembre’s contentions, none of the research articles cited in our systematic review proposed that increased attentional biases to food cues can only be demonstrated if direct comparison with ‘high-valenced/high-arousing stimuli’ is made. Similarly, this is not a methodological consideration in studies of addiction, where attentional bias to drug-related stimuli has been thoroughly investigated (6–8). Versace and Schembre also suggest that we are guilty of ‘overextrapolating the implications of reviewed literature’ based on ‘narrowly focused’ studies. On the contrary, our systematic review has highlighted the need for longitudinal experimental designs to delineate the relationship between salience attribution and excessive eating. The crosssectional design seen across the sampled literature is a limitation and is cited as such. We note ‘considering that all studies have employed either a cross-sectional or correlational research design the exact nature of the relationship between attentional biases to food cues and obesity is unable to be determined’. Fourth, the conclusion from Versace and Schembre’s electrophysiological data is that both obese and healthyweight groups tend to respond similarly to different types of stimuli, with responses to high-calorie stimuli only ‘somewhat larger’ than responses to neutral stimuli. As noted earlier, our interpretation of these findings is severely limited by the lack of access to the full text, and thus, it is impossible to assess the robustness of this approach. With the limited information available to us, we have several reservations that warrant mention: (i) conditions of hunger versus satiety have been demonstrated to alter eye movement results (9). It is unclear if both participant groups were fasted prior to testing. (ii) As demonstrated in our systematic review, the variability in stimuli presentation formats is quite possibly a source of variance across the results of the literature; to this end, the ability to detect fluctuations in attentional biases to food stimuli (especially when analysing mean event-related potential [ERP] amplitudes) may largely depend on the experimental design, and in particular, the extent to which participants are engaged by the task and the stimuli presented. (iii) Most notably, we question Versace and Schembre’s rationale for selectively basing their analysis on the late positive potential (LPP) waveform. The LPP is observed in ERPs in response to emotional stimuli and is thought to reflect emotional processing and sustained motivational processing (10,11). In a previously published study by Nijs et al. (4), the LPP waveform was used as an index of motivational salience and they were also unable to report between-group differences obesity reviews doi: 10.1111/obr.12300