**Background:** One-anastomosis gastric bypass (OAGB) is a combined restrictive and malabsorptive bariatric procedure gaining popularity worldwide. While nutritional deficiencies and malnutrition following OAGB have been studied, data on nutritional-related topics affecting food intake and compliance with lifestyle recommendations remain scarce. This study aimed to describe nutritional and lifestyle parameters following OAGB across two countries.
**Methods:** A multicenter cross-sectional study was conducted in Israel and Portugal. OAGB patients were recruited according to time elapsed since surgery: 1–6 months (1–6 M), 6–12 months (6–12 M), and 1–5 years (1–5 Y). Inclusion criteria were age ≥18 years and primary OAGB within the last 5 years; exclusion criteria included revisional surgery, pregnancy, and inability to consent. An anonymous online survey via SurveyMonkey® was administered between 26 June 2020 and 9 May 2021. The survey assessed demographics, anthropometrics (self-reported weight/height, BMI, %EWL), food tolerance (validated questionnaire, score range 1–27), appetite/taste/smell changes, compliance with bariatric surgery eating and lifestyle recommendations, and follow-up attendance. Statistical analyses used SPSS v26 with one-way ANOVA, Kruskal–Wallis, chi-square, or Fisher's exact tests as appropriate; significance set at p<0.05 with Bonferroni correction.
**Key Results:** A total of 277 responses from Israel (109 at 1–6 M, 59 at 6–12 M, 109 at 1–5 Y) and 111 from Portugal (40 at 1–6 M, 17 at 6–12 M, 54 at 1–5 Y) were obtained. Mean pre-surgery age was 41.6±11.0 years (Israel) and 45.6±12.3 years (Portugal); pre-surgery BMI was 41.2±4.8 and 40.1±5.6 kg/m²; 75.8% and 79.3% were female. Pre-surgery prevalence of type 2 diabetes was 17.0% (Israel) and 19.3% (Portugal); hypertension 25.6% and 44.0%; dyslipidemia 39.0% and 51.4%. Mean %EWL was 51.0±19.9% (Israel) and 62.4±26.5% (Portugal) in the 1–6 M group; 89.0±22.0% and 86.2±21.4% in the 6–12 M group; 89.9±23.6% and 98.2±20.9% in the 1–5 Y group (p<0.001 for both countries). Median weight regain at 1–5 Y was 2.8 kg (range 0–35.0 kg) in Israel and 2.0 kg (range 0–23.0 kg) in Portugal. Changes in appetite were reported by ≤94.0% (Israel) and ≤94.6% (Portugal) across groups. Changes in taste were reported by 51.0% and 51.4% (1–6 M), 46.6% and 43.8% (6–12 M), and 51.0% and 38.0% (1–5 Y) of Israeli and Portuguese respondents, respectively. Eating less due to bad taste or smell was reported by ≤23.5% (Israel) and ≤9.8% (Portugal). Food intolerances were most common for red meat, pasta, bread, and rice, with a trend toward better tolerance in longer-term groups. Mean food tolerance scores increased with time since surgery. Adherence to bariatric surgery eating recommendations was highest in the 1–6 M group but declined in longer-term groups in both countries. Daily multivitamin intake decreased with time in Israel (90.0% at 1–6 M, 84.9% at 6–12 M, 63.0% at 1–5 Y; p<0.001) but remained stable in Portugal (90.5%, 90.0%, 90.9%; p=1.000). Most respondents attended follow-up with a surgeon (≤94.0% Israel, 100% Portugal) and dietitian (≤92.6% Israel, ≤100% Portugal), but far fewer saw a psychologist/social worker (≤37.9% Israel, ≤56.1% Portugal). Physical activity targets (≥150 min/week) were met by a minority in both countries.
**Clinical Implications:** OAGB patients commonly experience changes in appetite, taste, and food intolerances that may impact dietary intake and nutritional status. Adherence to nutritional recommendations and multivitamin supplementation declines over time, particularly after the first postoperative year, which may increase risk of nutritional deficiencies and weight regain. These findings underscore the importance of long-term multidisciplinary follow-up including dietary counseling, physical activity promotion, and psychological support. Differences between Israeli and Portuguese cohorts suggest that health policies, clinical practices, and cultural factors influence adherence behaviors, indicating that interventions should be tailored to local contexts. Future prospective long-term studies are needed to further clarify the nutritional and lifestyle outcomes following OAGB.