Introduction Weight loss is a frequent complication in patients with cancer, and it is present in almost 85% of patients in some specific kinds of tumour. Malnutrition, decreased functional capacity and quality of life (QOL) contribute to an increased morbidity and mortality in these patients.

Objectives To evaluate the association among nutritional status, quality of life, index of fat free mass (FFMI) and functional capacity in patients undergoing chemotherapy.

Methods A prospective study was conducted in patients before the first chemotherapy course in the Hospital of Federal University of Pelotas, Brazil. Nutritional status was determined by Patient-Generated Subjective Global Assessment and quality of life by the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire. Bioelectrical impedance analysis and hand grip strength (HGS) were performed to evaluate FFMI and functional capacity, respectively.

Results 75 patients were evaluated, 74.7% had cancer of the digestive system. Only 12.8% of the patients were classified as well nourished. HGS median was 26 kg (IQR:18; 32 kg) FFMI median was 17.5 kg/m² (IQR:16.1; 18.8 kg/m²). Severely malnourished patients had a worse functional capacity (p=0.01); lower FFMI (p=0.005) and lower general QOF scores (p=0.03) than the nourished ones. A significant positive correlation was found between IFFM and HGS (r=0.51; p<0.001) and significant negative correlations between functional capacity and general QOL (r=−0.48; p<0.001) and HGS (r=−0.44; p<0.001).

Conclusions Malnutrition is a determining factor in the prognosis and QOL in these patients and it can be assessed by different parameters such as body composition, subjective evaluations or changes in functional capacity.