Oxalate Absorption and Dietary Intake

Medical history, dietary records, anthropometric, clinical, and 24 h urinary parameters were obtained from all patients at baseline under their usual, self-selected diet. Dietary intake of patients under their habitual diet was recorded using a 7-day food record. Patients provided a detailed description of the types and weighed amounts of all foods consumed. The nutrient composition of the foods was calculated using the PRODI 5.3 computer program (Nutri-Science GmbH, Freiburg, Germany). The oxalate content of the foods measured in our laboratory was entered into the database [21 (link),22 (link),23 (link)]. Sodium intake was estimated from 24 h urinary sodium excretion.
In the following phase, the patients were maintained on a balanced mixed standardized diet for 11 days [7 ]. After a few days of adaptation, this standardized diet, i.e., consistent daily intake of the prescribed foods and fluids, leads to a metabolic steady state, so that constant urinary values are achieved [7 ]. Fluid intake through beverages was 2.5 L per day. Patients collected 24 h urines during their self-selected diets and after 7 days on the standardized balanced diet. Gastrointestinal oxalate absorption of the patients was measured using the standardized [¹³C₂]oxalate absorption test [24 (link)]. The [¹³C₂]oxalate absorption test was conducted on days 9 and 10 under controlled, standardized conditions.