The impact of computed tomography-defined sarcopenia on outcomes in head and neck cancer has been well described. Sarcopenic obesity (SO) (depleted muscle mass combined with obesity) may pose a more serious risk than either condition alone.

We investigated SO and its impact on survival and critical weight loss (≥ 5 %) in patients with head and neck cancer who received curative radiotherapy (± other modalities). Retrospective analysis of computed tomography cross-sectional muscle at cervical (C3), thoracic (T2) and lumbar (L3) regions was conducted.

Patients were grouped by BMI and sarcopenia status based on established thresholds. A total of 413 patients were included for analysis, the majority having oropharyngeal carcinoma (52 %), and 56 % received primary concurrent chemoradiotherapy.

The majority of the cohort (65 %) was overweight or obese (BMI ≥ 25 kg/m). Sarcopenia was found in 43 %, with 65 % having SO ( 116), equating to 28 % of the whole cohort.

Critical weight loss was experienced by 58 % ( 238). A significantly higher proportion of patients with SO experienced critical weight loss ( 70 . 19, < 0·001) and were four times more likely to do so during treatment (OR 4·1; 95 % CI 1·5, 7·1; = 0·002).

SO was not found to impact on overall or cancer-specific survival; however, in patients with sarcopenia, those with SO had better overall survival (median 9·1 . 7·0 years; 95 % CI 5·2, 16·8; = 0·021). SO at the time of presentation in patients with head and neck cancer is predictive of critical weight loss during treatment, and muscle evaluation can be useful in identifying patients at nutritional risk regardless of BMI and obvious signs of wasting.