PMC:4137988 / 4803-9288 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/4137988","sourcedb":"PMC","sourceid":"4137988","source_url":"https://www.ncbi.nlm.nih.gov/pmc/4137988","text":"Methods\nWe followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement to prepare the manuscript.15\n\nLiterature search strategy\nAn electronic literature search was conducted using Medline (PubMed), Scopus, and ISI Web of Knowledge in January 2014 and extended back to 1950. The terms used to search titles and abstracts were (asthma OR wheezing OR wheeze OR lung function) AND (diet OR dietary OR food pattern). Further details on the literature search are shown in the Appendix 1. Only original studies with human subjects and published in English were included. In addition, cross-referencing from the articles found was used to complete the search. To be included in the systematic review, a study needed to have at least one dietary pattern predefined and measured (eg, Mediterranean) or generated from usual dietary intake using a multivariate statistical method and examine the effect or association of the dietary pattern(s) with one or more asthma outcome.\n\nInclusion criteria\nThe meta-analysis included studies of dietary patterns and asthma prevalence in adults meeting the following criteria: primary outcomes included prevalence of current or ever asthma, which was most commonly reported in the reviewed studies for adults (the number of studies assessing other asthma outcomes was too small to perform a meta-analysis); a dietary pattern score was calculated or dietary patterns were identified using a statistical method such as principal component analysis (PCA; selective solo or oligo food groups, eg, fruit and vegetables or fruit and fish, were not eligible); and odds ratio (OR) was calculated to determine the association between the dietary pattern(s) and asthma prevalence. Two researchers (NL and LX) independently reviewed the identified relevant articles and judged whether they met the inclusion criteria for meta-analysis. Uncertainties and discrepancies were resolved by consensus after discussing with a senior researcher (JM).\n\nQuality assessment\nThe same two researchers (NL and LX) independently rated all the research articles included in the systematic review using the American Dietetic Association Quality Criteria Checklist.16 The scientific soundness of the articles was rated using ten validity questions. Based on the answers, one of the three quality ratings was assigned: positive (answered “yes” to six or more validity questions, including four priority questions), negative (answered “no” to six or more validity questions), or neutral (the rest of the situations). Only articles with a positive or neutral quality rating were included in the meta-analysis.\n\nAssessment of dietary patterns and data extraction\nWhen statistically derived using PCA or factor analysis, usually multiple dietary patterns were reported. Two researchers (NL and LX) independently grouped all dietary patterns into three categories: healthy, unhealthy, or neutral, based on constituent foods of each pattern suggested by PCA or main factor loadings. Any disagreements were discussed with the senior researcher (JM). Table 1 shows dietary patterns, categories, and constituent foods. A healthy dietary pattern was characterized by high intakes of fruit, vegetables, whole grains, and/or fish. An unhealthy dietary pattern tended to have high loadings of refined grain, red meat, processed meat, fast foods, high sugar foods, and/or high fat foods. A neutral dietary pattern generally consisted of a mixture of healthy and unhealthy food items. The same two researchers (NL and LX) independently extracted the data to be used for meta-analysis.\n\nStatistical analysis\nWe performed a meta-analysis to evaluate the association of dietary patterns with asthma prevalence in adults. Studies reported dietary pattern scores either as continuous variables or categorized them into tertiles or quintiles. Linear mixed models were used to derive the pooled effect sizes and 95% confidence intervals (CIs) for healthy, unhealthy, and neutral dietary patterns and to assess heterogeneity between studies.17 In addition, heterogeneity and publication bias were visually evaluated using Begg’s funnel plots, which displayed the scatter patterns of effect estimates against standard errors from the included studies, with a vertical line indicating the pooled estimate and diagonal lines showing the expected 95% CIs around the estimate.18 All statistical analyses were conducted using SAS version 9.2 (SAS Institute Inc., Cary, NC, USA).","divisions":[{"label":"title","span":{"begin":0,"end":7}},{"label":"p","span":{"begin":8,"end":138}},{"label":"sec","span":{"begin":140,"end":1003}},{"label":"title","span":{"begin":140,"end":166}},{"label":"p","span":{"begin":167,"end":1003}},{"label":"sec","span":{"begin":1005,"end":1997}},{"label":"title","span":{"begin":1005,"end":1023}},{"label":"p","span":{"begin":1024,"end":1997}},{"label":"sec","span":{"begin":1999,"end":2643}},{"label":"title","span":{"begin":1999,"end":2017}},{"label":"p","span":{"begin":2018,"end":2643}},{"label":"sec","span":{"begin":2645,"end":3605}},{"label":"title","span":{"begin":2645,"end":2695}},{"label":"p","span":{"begin":2696,"end":3605}},{"label":"title","span":{"begin":3607,"end":3627}}],"tracks":[{"project":"2_test","denotations":[{"id":"25143747-19631508-55576475","span":{"begin":136,"end":138},"obj":"19631508"},{"id":"25143747-7786990-55576476","span":{"begin":4384,"end":4386},"obj":"7786990"}],"attributes":[{"subj":"25143747-19631508-55576475","pred":"source","obj":"2_test"},{"subj":"25143747-7786990-55576476","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"2_test","color":"#93ecec","default":true}]}]}}