**2. Methods**

The current study was completed according to the Preferred Reporting Items for the Systematic reviews and Meta-Analyses (PRISMA) guidelines [25,26] and registered in the PROSPERO registry, York, UK—Association between smoking shisha, obesity, and related comorbidities: a systematic review (CRD42019129389) [27].

#### *2.1. Inclusion and Exclusion Criteria*

All studies evaluating hookah smoking and obesity were included, provided they met the following criteria: (i) they were written in English, (ii) they were original articles, and (iii) they related to prospective or retrospective observational (analytical or descriptive), experimental, or quasi-experimental controlled or noncontrolled studies. Reviews or non-original articles (e.g., case reports, editorials, letters to editors, or book chapters) were excluded.

#### *2.2. Information Source and Search Strategy*

The literature search was designed and performed independently in duplicate by two of the authors: the principal and the senior investigator. The PubMed/MEDLINE database was systematically screened using the following MeSH terms: #1 = Obesity, #2 = Hookah, #3 = Water pipe, #4 = Narghile, #5 = Arghile, and #6 = Shisha, together with the combinations #1 AND #2 OR #3 OR #4 OR #5 OR #6. In addition, a manual search was carried out to retrieve other articles that had not been identified via the initial search strategy. The publication date was not considered as an exclusion criterion for the purposes of this review.

## *2.3. Study Selection*

Two authors independently screened the resulting articles for their methodologies and appropriateness for inclusion. All the included studies underwent a risk-of-bias assessment according to the 10-item quality assessment checklist for prevalence studies adapted by Hoy and colleagues, in which a total score of 0–3 indicates a low risk of bias, a score of 4–6 indicates a moderate risk of bias, and a score of 7–9 indicates a high risk of bias [28]. Consensus discussions were used to resolve disagreements between reviewers.

#### *2.4. Data Collection Process and Data Items*

The title and abstract of each paper were firstly assessed by two independent authors for language suitability and subject-matter relevance, and the studies selected were assessed in terms of their appropriateness for inclusion and the quality of the method. Those studies passing both rounds of screening are shown in Table 1.


