Background: Self-rated health (SRH) is a validated, patient-centered proxy for overall physiological reserve and an independent predictor of survival in people living with and beyond cancer. Although malnutrition is highly prevalent among cancer survivors, it remains unclear how specific dietary and circulating nutritional biomarkers jointly map onto the perceived health of this population. Objective: To quantify the independent associations of dietary and blood-based nutritional indicators with SRH in a sample of U.S. adult cancer survivors, and to explore potential effect modification by sex and systemic inflammation. Methods: We analyzed data from adults who reported a physician diagnosis of cancer or malignancy in the National Health and Nutrition Examination Survey (NHANES). The outcome was SRH, an ordinal five-level variable (1 = excellent to 5 = poor). Exposure indicators comprised mean two-day dietary fiber intake, serum pyridoxal 5’-phosphate (vitamin B6), red-blood-cell folate (vitamin B9), mean two-day vitamin B12 intake, serum triglycerides, and body-mass index. Multivariable ordinal logistic regression was used to estimate adjusted odds ratios (ORs) with 95% confidence intervals (CIs). Pre-specified stratified analyses were performed by sex and subgroup analyses by C-reactive protein (CRP) status (< 1 vs. ≥ 1 mg/dL). Restricted cubic splines (RCS) characterized dose–response shapes. Results: A total of 308 cancer survivors (mean age 53.2 ± 13.0 years; 61.7% female) were included; 86 (27.9%) reported fair or poor health. In the fully adjusted model, higher dietary fibre (OR 0.949 per 1 g/day; 95% CI 0.922–0.977; p = 0.0005), vitamin B6 (OR 0.994 per 1 nmol/L; 0.990–0.997; p = 0.0006) and vitamin B12 (OR 0.922 per 1 mcg; 0.857–0.991; p = 0.028) were independently associated with lower odds of poorer SRH, while higher RBC folate showed a protective trend that did not reach conventional significance (OR 0.999 per 1 ng/mL; 0.998–1.000; p = 0.055); in contrast, higher triglycerides (OR 1.003 per 1 mg/dL; 1.001–1.006; p = 0.001) and BMI (OR 1.031 per 1 kg/m²; 1.003–1.059; p = 0.028) were associated with poorer SRH. Stratified analyses indicated that the protective association of dietary fiber was statistically robust in female survivors (OR 0.921 per 1 g/day; 0.885–0.959; p < 0.001) but not in males, and that the beneficial profile of fiber, vitamin B6 and vitamin B12 persisted in the low-inflammation (CRP < 1 mg/dL) subgroup. RCS analyses confirmed largely monotonic dose–response relationships without obvious threshold effects. Conclusion: Among U.S. adult cancer survivors, a more favorable nutritional profile, higher dietary fiber, vitamins B6 and B12 (with a consistent protective trend for vitamin B9), together with lower triglycerides and healthier BMI, was independently associated with better self-rated health. These findings support dietary and metabolic optimization as a pragmatic, modifiable lever for improving perceived health in cancer survivorship and warrant confirmation in longitudinal cohorts.