Aims: This study aims to determine the characteristics of patients indicated for I-131 treatment following complete thyroidectomy. The findings will assist Vietnamese nutritionists in developing appropriate guidelines and intervention methods.

Methods: This cross-sectional study was conducted at Hanoi Oncology Hospital from April 2021 to December 2022. Body weight, height, arm and calf circumference were measured. Body mass index (BMI) was calculated, and Patient Generated Subjective Global Assessment (PG-SGA) was assessed. The 24-hour dietary recall was assessed in comparison to patient’s energy and protein daily requirements.

Results: Based on BMI, 15.3% of patients were overweight or obese, while 9.6% were malnourished. Arm and calf circumferences were effective indicators of malnutrition risk, similar to the PG-SGA. Despite 91.1% reporting no dietary changes, 40.3% experienced weight loss. Common symptoms included difficulty swallowing, loss of appetite, and fatigue. Dietary intake met 60.6 ± 24.6% of energy and 48.8 ± 20.6% of daily protein requirements.

Conclusions: A predominant rate of overweight-obesity (33.1%) was found in the thyroid cancer patients. Their energy and protein intake were inadequate. Dietary counseling is recommended to ensure iodine restriction, adequate nutrition, and prevent weight gain after I-131 treatment.