**3. Results**

The initial search retrieved 818 papers. After the first round of screening (titles and abstracts), 408 papers were excluded on the following grounds: They were not in English or did not study humans, or the abstracts and full texts were not available. The second round of screening excluded articles (n = 326) that represented an inappropriate type of paper, were not an original research article, (e.g., reviews, letters to editors, book chapters, and case reports), or were not related to smoking or obesity and related comorbidities. Of the remaining 84 articles dealing with smoking and health status, a further 79 papers were excluded on the following grounds: They were on smoking but not on hookahs, they considered health outcomes other than obesity and related comorbidities (e.g., cancer, respiratory diseases, acute effects of hookah-smoking such as heart rate, etc.), or other factors, (e.g., they were conducted in clinical settings rather than in the general population). Thus, at the end of the screening process, five articles were available for systematic review, narrative synthesis, and meta-analysis (Figure 1). According to the quality assessment checklist for prevalence studies (n = 5), these studies had a low risk of bias (mean score of 1.2 points) (Table 2).

**Figure 1.** The flowchart summarizing the study selection procedure.


**Table 2.** Quality assessment checklist for prevalence studies.

## *3.1. Narrative Synthesis*

In 2012, Shafique et al. [32] conducted a cross-sectional population-based study to investigate the association between hookah smoking and metabolic syndrome as a primary outcome. The sample included 2032 individuals, of which 325 were current hookah smokers. Metabolic syndrome was significantly higher among the current hookah smokers (33.1%) compared to nonsmokers (14.8%); the former were three times more likely to have metabolic syndrome compared with nonsmokers after an adjustment for confounders. Moreover, the definition of obesity was based on waist circumference. For abdominal obesity, the authors used a South Asian-specific cutoff of ≥90 cm waist circumference for males and of ≥80 cm for females [33]. In fact, hookah smokers had a significantly greater waist circumference (84.7 ± 12.6 vs. 80.6 ± 11.8; *p* < 0.01), and a logistic regression analysis showed that hookah smokers were significantly more likely to show abdominal obesity (OR 1.93, 95% CI 1.52–2.45).

In 2015, Ward et al. [34] conducted a population-based household study among 2536 adults (age ≥ 18 years) and examined the associations between hookah smoking and BMI and obesity status (BMI ≥ 30 kg/m2). Of the total sample 2134 had never smoked a hookah, 116 were former smokers, 251 were current non-daily smokers, and 35 were current daily smokers. The mean BMI of the entire sample was 30.2 ± 6.3 kg/m2. The authors found that daily hookah smokers had a BMI nearly 2 units greater than nonsmokers and had nearly three times the risk of obesity.

In 2018, Saffar Soflaei et al. [35] published a large population study with a total of 9840 subjects living in the city of Mashad (Iran), allocated to five different groups: nonsmokers (n = 6742), ex-smokers (n = 976), cigarette smokers (n = 864), hookah smokers (n = 1067), and cigarette and hookah smokers (n = 41). The authors found a significant association between hookah smoking (not cigarette-smoking) and obesity. They concluded that, in contrast to the common belief that the hookah eliminates the toxicity of tobacco compared with cigarettes, the adverse effects of hookah smoking could be even greater than those of cigarette smoking. In fact, in this study, the prevalence of obesity was significantly higher in hookah smokers compared with nonsmokers and even cigarette smokers.

In 2018, Alomari et al. [36] studied the associations between obesity and hookah smoking among 2313 adolescents of both genders at public schools in grades seven to 10 in Jordan using a cross-sectional design. The BMI percentile z-scores were calculated to determine weight-status categories, and obesity was defined as the 95th percentile or greater. Of the entire sample, 279 (12.1%) were obese. The authors found that body weight and age- and gender-specific BMI were higher for hookah smokers compared to nonsmokers and that those who smoked a hookah weekly had double the odds of being obese compared to nonsmokers (OR = 2.14; 95% CI = 1.08–4.21; *p* = 0.028). They concluded that hookah use and dual use are associated with greater obesity, BMI, and body weight among Jordanian adolescents.

In 2018, Hasni et al. [37] undertook a small population study that aimed to compare the biochemical and metabolic profiles of hookah smokers and nonsmokers in 58 young males aged between 25 and 45 with no known history of metabolic or cardiovascular diseases. Abdominal obesity was defined based on the International Diabetes Federation (IDF) criteria, i.e., WC ≥ 94 cm [38], and obesity was defined as BMI ≥ 30 kg/m2. The mean BMI in hookah smokers was significantly higher than that of nonsmokers (28.2 ± 3.6 vs. 26.5 ± 2.6; *p* = 0.046), and there was a higher prevalence of obesity (37.9% vs. 6.9%; *p* = 0.04) and a higher prevalence of abdominal obesity (79.3% vs. 59.6%; *p* = 0.08) among hookah smokers.
