OBJECTIVE:The study objective was to determine the dietary intake of patients with chronic kidney disease before and after filtering for suspected underreporters and to investigate the impact of underreporting on the interpretation of diet data. DESIGN:This was a cross-sectional study. SETTING:The study included outpatients from hospitals and clinics in Northern Tasmania, Australia. PATIENTS:Data from 113 patients enrolled in the Lipid Lowering and Onset of Renal Disease trial were used in this study. Patients with serum creatinine greater than 120 mmol/L were included, and those taking lipid-lowering medication were excluded. METHODS:Patients completed a 4-day self-report diet diary, and FoodWorks software was used to determine their daily intake of energy, macronutrients, and specific micronutrients. Diet diaries were assessed for likely underreporting using the Goldberg cutoff approach with a ratio of energy intake to estimated resting energy expenditure of 1.27. Nutrient intakes were compared with current National Kidney Foundation's Kidney Disease Outcomes Quality Initiative guidelines, World Health Organization recommendations, recommended daily allowances, and daily values adjusted for energy intake. RESULTS:Demographics of the patients were as follows: male/female, 71/42; age (mean +/- standard deviation), 60 +/- 15 years; body mass index, 28.6 +/- 6.0 kg/m(2), and serum creatinine, 223.4 +/- 110.0 mmol/L. According to the criteria, 80 patients (70.8%) were underreporting their energy intake. Underreporters were more likely to be female and younger, and have a higher body mass index and elevated serum creatinine. In all patients, daily energy intake (89.6 +/- 32.4 kJ/kg) was lower than recommended (125-145 kJ/kg); however, this was not the case for valid reporters (128.3 +/- 23.7 kJ/kg). Protein intake was higher (0.9 +/- 0.3 g/kg) than recommended (0.75 g/kg) in all patients and even higher (1.2 +/- 0.3 g/kg) in valid reporters. Mean calcium, zinc, and dietary fiber intakes were all below recommendations in all patients, but these differences were not apparent in valid reporters. CONCLUSION:Interpreting self-report diet diary data from patients with chronic kidney disease without attempting to exclude underreporters will lead to erroneous conclusions, especially in respect to energy, protein, dietary fiber, calcium, and zinc intakes.