This descriptive cross-sectional study was conducted over 3 months (November 2023 to January 2024) and included physically active adults residing in the Eastern Province of Saudi Arabia. The study did not aim to compare governorates or specific forms of physical activity; rather, it sought to provide an overall picture of dietary supplement use among active adults in the region. The research adopted a quantitative design and relied on closed-ended questionnaire items.

The study sample consisted of Saudi adults living in the Eastern Province who consistently participated in physical exercise (e.g., fitness club members, gym participants, and independent exercisers). The inclusion criteria were: (a) Saudi nationality, (b) age 18–60 years, (c) consistent PA for ≥12 consecutive weeks, (d) provision of informed consent, and (e) submission of a complete questionnaire. Individuals with chronic diseases limiting PA were excluded.

A non-probability quota sampling strategy was used due to the absence of a comprehensive sampling frame for physically active adults in the Eastern Province of Saudi Arabia and the practical constraints associated with recruiting this population using probability-based methods. Because gym members and recreational exercisers are not registered in any unified database from which individuals could be randomly selected, probability sampling was not feasible and was therefore ruled out. Quota sampling enabled balanced representation across key sociodemographic groups (sex and age categories: 18–29, 30–44, and ≥45 years) while maintaining operational feasibility in terms of time, cost, and access to recruitment sites. This approach enhanced subgroup coverage and supported the study’s exploratory objective of examining patterns and associations; however, it does not permit full probabilistic generalization to the wider provincial population.

Participants were recruited using a multi-channel strategy that comprised direct collaboration with fitness clubs, online distribution via social media platforms (X, Instagram, and WhatsApp), and on-site recruitment at supplement stores and community events. To increase diversity and eliminate selection bias, data were collected from different cities in the Eastern Province, including Dammam, Khobar, Qatif, and Al-Ahsa. The limitations associated with this sampling method are acknowledged, and the findings should be interpreted with consideration of potential restrictions in external validity beyond the province.

The required sample size was estimated using Cochran’s formula, considering a 95% confidence level, a 5% margin of error, and a 22% predicted prevalence based on previous research (15). This calculation yielded a minimum required sample size of 264, which was increased to 330 to account for anticipated non-responses and dropouts.

Data collection occurred in two phases. First, a pilot study with 34 participants assessed the clarity, structure, and comprehensibility of the questionnaire, resulting in minor linguistic revisions. In the second phase, data were collected from the remaining participants. The study was approved by the Ethics Committee of King Faisal University’s Deanship of Scientific Research (Ref: KFU-REC-2023-OCT-ETHICS1589) and conducted in accordance with the Declaration of Helsinki. All participants provided written or electronic informed consent, and confidentiality was ensured through anonymization and secure, encrypted data storage.

All statistical analyses were performed using SPSS Statistics (version 26; IBM Corp., Armonk, NY, USA), with a two-tailed p < 0.05 considered statistically significant. The data was screened and cleaned before analysis. Normality was assessed using standard criteria for skewness (|skewness| < 2) and kurtosis (|kurtosis| < 7), supplemented by visual examination of Q–Q plots. Univariate outliers were defined as values exhibiting an absolute Z-score exceeding 3 (|Z| > 3). Extreme values were winsorized to reduce their influence while maintaining the integrity and rank order of the data, substituting them with the nearest non-outlier value within the variable distribution. The participants’ sociodemographic characteristics, PA patterns, and supplement-related behaviors were summarized descriptively, using means ± standard deviations (SDs) for normally distributed continuous variables and frequencies (percentages) for categorical variables.

Continuous variables were compared between dietary supplement users and non-users using independent samples t-tests, and among sex × dietary supplement use groups using two-way analysis of variance (ANOVA) with post-hoc Tukey’s tests. Categorical variables were compared between dietary supplement users and non-users using chi-square (χ²) tests. To ensure transparency and interpretability, effect sizes were estimated using eta-squared (η²) for ANOVA (small ≈ 0.01, medium ≈ 0.06, and large ≈ 0.14), Cohen’s d for t-tests (small ≈ 0.2, medium ≈ 0.5, and large ≈ 0.8), and Cramer’s V for chi-square tests (small ≈ 0.10, medium ≈ 0.30, and large ≈ 0.50).

A total of 793 questionnaires were returned, of which 38 were excluded due to incomplete responses (<90% completion), non-serious or patterned answers, or failure to meet the inclusion criterion of regular physical activity. The final sample comprised 755 participants, exceeding the planned sample size.

The sample included 379 males (50.2%) and 376 females (49.8%), reflecting balanced sex representation. Participants’ ages ranged from 18 to 50 years, with a mean of 29.61 ± 8.06 years. They had a mean weight of 71.35 ± 18.05 kg, a mean height of 166.82 ± 10.37 cm, and a mean BMI of 25.53 ± 5.60 kg/m², reflecting a generally healthy population with moderate anthropometric variability (Table 1).

Regarding body type, 384 participants (50.9%) had a healthy weight, 251 (33.2%) were overweight, and 90 (11.9%) were obese. BMI differed significantly by sex (χ² = 30.4, p < 0.001, V = 0.201), with males more frequently overweight and females more frequently underweight. Most participants were single (n = 419, 55.5%), followed by married (n = 291, 38.5%) and divorced (n = 30, 4.0%); 15 participants (2.0%) did not disclose marital status. Regarding occupation, participants were primarily employed in the private sector (n = 246, 32.6%), government (n = 190, 25.2%), or education (n = 188, 24.9%). Most reported a monthly household income of 5,000–14,999 SAR (41.4%), and the majority held a bachelor’s degree (n = 389, 51.5%).

The participants’ behavioral characteristics are presented in Table 2. Over half (n = 406, 53.8%) reported exercising more than four times per week, and 162 (21.5%) identified as an athlete. Exercise frequency was significantly higher among males than females (χ² = 67.15, p < 0.001, V = 0.298). Most participants reported multiple motivations for PA (n = 399, 52.8%), followed by enjoyment (n = 134, 17.7%), aesthetics (n = 120, 15.9%), and health reasons (n = 82, 10.9%). Motivations did not differ significantly by sex (χ² = 3.03, p = 0.696, V = 0.063).

Among the participants, 505 (66.6%) reported taking dietary supplements, while 250 (33.4%) did not. The number of users and non-users was generally balanced and did not differ significantly between males (65.96% vs. 34.04%) and females (67.82% vs. 32.18%, χ² = 0.294, p = 0.588, V = 0.02).

The participants’ age and anthropometric parameters are presented by sex and dietary supplement use in Table 3. The distribution of age, weight, height, and BMI did not differ significantly between users and non-users (t = 0.32–1.68, p = 0.093–0.975, d = 0.02–0.19), suggesting that these characteristics do not strongly predict dietary supplement use. Expected sex-based differences were observed, with males taller and heavier than females (F = 61.93–221.66, p < 0.001, η² = 0.20–0.47), while BMI differences were smaller but significant (F = 5.39, p = 0.001, η² = 0.02).

Post-hoc Tukey’s tests showed small but significant differences in age and BMI across the sex × supplement-use groups. Female participants were younger than males among both users (28.39 ± 8.03 vs. 30.87 ± 7.66 years) and non-users (27.80 ± 7.98 vs. 31.21 ± 8.33 years; p = 0.003–0.005, η² = 0.03). For BMI, male users (26.59 ± 6.17 kg/m²) had higher values than female users (24.97 ± 5.25 kg/m²) and female non-users (24.45 ± 4.69 kg/m²). Male non-users (25.57 ± 5.58 kg/m²) also had higher BMI than female users (24.97 ± 5.25 kg/m², p = 0.003–0.006, η² = 0.02). Overall, these results indicate that dietary supplement use is mainly independent of basic anthropometric characteristics, highlighting the likely influence of psychological, behavioral, or knowledge-based factors in this population.

Cohen’s d was calculated for the t-test comparing users vs. non-users, and η² was calculated for the ANOVA comparing the sex × dietary supplement use groups. No significant differences were found between users and non-users in the total sample, suggesting that physical characteristics do not predict dietary supplement use. As expected, sex explains moderate variation in weight and height.

The participants’ demographic characteristics are presented by sex and dietary supplement use in Table 4. Participants with normal weight predominated across all subgroups, while those who were underweight were more common among female users (n = 20, 8.0%) than among male (n = 2, 0.8%) users and non-users (n = 1, 0.76%). Body type (χ² = 33.855, p < 0.001, V = 0.12), occupation (χ² = 127.089, p < 0.001, V = 0.41), and education level (χ² = 34.287, p = 0.001, V = 0.21) differed significantly across sex × dietary supplement use groups, but not monthly household income (p = 0.067). These findings indicate that dietary supplement use is moderately associated with sex-specific patterns in body type, occupation, and education level but not with monthly household income.

The behavioral patterns, encompassing training frequency and motivations, were broadly similar between dietary supplement users and non-users (Table 5). Most participants engaged in frequent training, with more than half exercising more than four times per week among users (51.9%) and non-users (57.6%). Additionally, about one-fifth identified primarily as athletes among both users (22.4%) and non-users (19.6%). Just over half of participants reported multiple motivations for training among users (52.1%) and non-users (54.4%). In contrast, few participants reported financial gain or social integration as motivations (<2%).

Training frequency differed significantly among the sex × dietary supplement use groups (χ² = 71.18, p < 0.001, V = 0.31), with a medium effect size. Post-hoc comparisons among non-users showed that males were significantly more likely to train >4 times/week than females (χ² = 28.47, p < 0.001, V = 0.35). In contrast, females were more likely to train once/month than males (χ² = 18.45, p = 0.001, V = 0.25) or once/week (χ² = 7.92, p = 0.005, V = 0.18). No significant differences were noted between those who trained >4 times/month and those who were primarily athletes.

Among users, male participants were significantly more likely to train >4 times per week than female participants (χ² = 36.72, p < 0.001, V = 0.38), while females were more likely to train >4 times/month than males (χ² = 10.3, p = 0.004, V = 0.21). No significant differences were observed for once/month, once/week, or primarily athlete categories (p > 0.05). These findings indicate consistent sex-specific patterns in training frequency, with males generally engaging in higher-frequency training, regardless of dietary supplement use, and females showing greater representation in lower-frequency training categories.

The motivation for training did not differ significantly among the sex × dietary supplement use groups (χ² = 20.49, p = 0.154, V = 0.16). Therefore, these findings indicate that dietary supplement use is primarily independent of training motives but is partially correlated with training frequency, particularly highlighting elevated physical activity levels among males.

Our findings indicated no significant differences in age, weight, height, or BMI between dietary supplement users and non-users, suggesting that the choice to take dietary supplements within the study population is primarily influenced by psychological or behavioral factors rather than physical attributes. This observation aligns with previous studies on recreationally active populations reporting no significant association between anthropometric indices and supplement use (5, 6, 33).

In our study, males exhibited significantly greater heights and weights compared to females (η² = 0.20–0.47), consistent with recognized biological sex-based differences in body composition (16). However, sex-based differences in BMI were minimal (η² = 0.02), indicating comparable body mass relative to height across sexes.

Post-hoc Tukey’s tests revealed small but significant differences in age and BMI across the sex × dietary supplement use groups. Regardless of their dietary supplement use status, females were generally younger than males (p = 0.003–0.005, η² = 0.03), possibly reflecting a broader national trend of increasing fitness participation among younger women (34). Male users had marginally higher BMIs than both female users and non-users (p = 0.003–0.006), likely related to greater muscle mass or training intensity (33, 35). These minor differences did not correspond to higher dietary supplement use, reinforcing that body composition is not a primary driver of dietary supplement use.

Collectively, these results suggest that dietary supplement use among Saudi adults is more strongly associated with cognitive, motivational, and sociocultural factors than with physical characteristics, consistent with prior evidence emphasizing psychological predictors such as appearance orientation and self-enhancement (29, 36).

Most participants had a normal weight across all sex × dietary supplement use groups, whereas being underweight was more common among female users than among male users and non-users. This observation may indicate that sociocultural and psychological factors influence women’s perceptions of weight and their decisions to use dietary supplements. Research among young women in the region has found that body image concerns and exposure to social media are associated with weight-management behaviors, including dietary supplement use for aesthetic enhancement (29, 34, 37).

Significant associations were observed between dietary supplement use and body type, occupation, and education, but not monthly household income. Occupation exhibited the largest effect (V = 0.41), indicating that lifestyle and exposure to a gym culture play major roles. Higher education may indirectly influence supplement use by enhancing health awareness and facilitating access to occupations embedded in gym culture (38–40). Students and private-sector employees exhibited the highest use of dietary supplements, possibly due to peer influence and fitness engagement (16, 41). Conversely, those who were unemployed and government employees had lower use of dietary supplements, potentially reflecting differences in age, time availability, or routine PA. Although these interactions cannot be directly tested in the present cross-sectional analysis, they highlight potential mechanisms by which sociodemographic and lifestyle factors may shape supplement use, which will be explored further in Part II of our research project. The positive association between dietary supplement use and higher education aligns with studies showing that educated individuals exhibit greater health awareness and belief in the benefits of dietary supplements (17, 42). The lack of a significant effect for monthly household income suggests that lifestyle and knowledge, rather than financial capacity, are more influential determinants of dietary supplement use.

Behavioral patterns, including training frequency and motivation, were generally similar between dietary supplement users and non-users but differed significantly by sex. Over half of the participants trained more than four times per week, reflecting high overall levels of PA in the sample. This observation aligns with national data showing rising exercise participation under Vision 2030 initiatives (34, 43).

Training frequency differed significantly across the sex × dietary supplement use groups [χ² = 71.18, p < 0.001, V = 0.31 (medium effect size)]. Male users and non-users were more likely to train more than four times per week, whereas female non-users were more likely to exercise once a week or once a month. This pattern suggests that dietary supplement use is associated with greater training engagement, particularly among men, consistent with evidence linking dietary supplement use to training volume and gym attendance (33, 41, 44).

No significant difference in training motivation was observed across the sex × dietary supplement use groups (χ² = 20.49, p = 0.154, V = 0.16). Most participants cited multiple motives for exercising, supporting the self-determination framework, which posits that intrinsic and extrinsic motivations frequently coexist (30, 31). Thus, dietary supplement use appears to correlate more with behavioral engagement, particularly training frequency, than with motivational orientation. The higher training frequency and dietary supplement use among males may reflect greater cultural and environmental access to sports facilities, while lower participation among females could stem from ongoing sociocultural barriers or time constraints (43). Overall, our findings emphasize the importance of sex-responsive health promotion to ensure equitable access to exercise and reliable information about dietary supplements.

Our study had several limitations that should be acknowledged. Firstly, its cross-sectional design prevents causal inference. Secondly, the self-reported data, including weight and height, may be affected by recall bias or social desirability, which could influence BMI calculations. Thirdly, the use of non-probability quota sampling limits the generalizability of our findings beyond the Eastern Province. Fourthly, nutrient intake or dietary supplement dosage was not assessed, which limits the interpretation of adequacy and safety. Notably, adverse effects and inadvertent doping will be discussed in our subsequent paper reporting Part II of the research project. Despite these limitations, the large and diverse sample examined in this study provides valuable insights into dietary supplement use patterns, supporting future longitudinal and interventional research.