**Background:** Vegetarianism is gaining global popularity, but data on its prevalence and associated factors in Arab countries, particularly Saudi Arabia, are lacking. This study aimed to investigate knowledge, attitudes, and factors associated with vegetarianism in the Saudi population.
**Methods:** This cross-sectional study was conducted from May 2020 to September 2020. An electronic questionnaire was distributed via social media platforms (Facebook, Twitter, LinkedIn, WhatsApp) using snowball sampling. The questionnaire included sociodemographic questions, reasons for following a vegetarian diet, and beliefs/knowledge about vegetarianism. Knowledge was assessed using four questions; participants answering ≤2 correctly were classified as having low knowledge. Pregnant/lactating women and those with chronic diseases were excluded. Data were analyzed using SPSS version 23.0, with chi-square tests and multivariate binary logistic regression. Significance was set at P≤0.05.
**Key Results:** Of 3,265 responses collected, 3,035 were completed (93% response rate). Participants were 80.2% female and 19.8% male, aged 18–65 years. The prevalence of self-reported vegetarianism was 37.5% (n=1,197), comprising 15.7% semivegetarians, 8.1% pesco-vegetarians, 64.3% lacto-ovo-vegetarians, and 11.3% vegans. Among vegetarians, 47.6% had followed the diet for 1–5 years. Health reasons were the most common motivator (72.5%), followed by ethical concerns (59.3%) and environmental concerns (47.9%). Other reasons included dislike of meat (33.7%), concerns about hormones in meat (36.9%), weight loss (16.2%), and spiritual reasons (16.2%). Social media was the primary information source for 62.7% of vegetarians. The top challenge was difficulty finding meat/dairy substitutes (17.5%), followed by cultural norms (14.9%). Knowledge levels were low: 92.9% of vegetarians and 64.3% of nonvegetarians had low knowledge. Multivariate logistic regression identified factors significantly associated with increased likelihood of vegetarianism: exercising half an hour/day (OR 1.714, 95% CI 1.414–2.077, P<0.001), one hour/day (OR 2.321, 95% CI 1.872–2.877, P<0.001), and two hours/day (OR 2.321, 95% CI 2.742–5.662, P<0.001). Factors associated with decreased likelihood included: male sex (OR 0.336, 95% CI 0.259–0.434, P<0.001), age 51–64 years (OR 0.204, 95% CI 0.068–0.616, P=0.004), being married (OR 0.45, 95% CI 0.341–0.592, P<0.001), higher education (OR 0.419, 95% CI 0.214–0.819, P=0.011), working in the health sector (OR 0.542, 95% CI 0.337–0.872, P=0.012), being a housewife (OR 0.507, 95% CI 0.277–0.931, P=0.028), and income of 5,000–10,000 SR/month (OR 0.637, 95% CI 0.472–0.861, P=0.003). Vegetarians had significantly higher rates of depression (P<0.001) and anxiety (P<0.001), while nonvegetarians had higher rates of anemia (P<0.001), thyroid disorders (P=0.002), diabetes (P=0.033), CVD/hypertension (P=0.017), and abnormal lipid profiles (P<0.001).
**Clinical Implications:** This first-of-its-kind study in Saudi Arabia reveals a substantial prevalence of self-reported vegetarianism (37.5%), though this may reflect selection bias. The very low knowledge levels (92.9% of vegetarians) highlight a critical need for evidence-based nutritional education, particularly given the risk of deficiencies in vitamin B12, iron, and calcium. The association between vegetarianism and higher rates of depression/anxiety warrants further investigation, possibly related to nutrient deficiencies. Conversely, the lower prevalence of cardiometabolic diseases among vegetarians supports potential health benefits. Healthcare providers should proactively assess dietary patterns, provide guidance on balanced vegetarian nutrition, and monitor for potential deficiencies. Public health initiatives through the Ministry of Health could improve vegetarian nutrition literacy and expand vegetarian food options in Saudi society.