Urine collection and analysis
To measure zinc absorption, we collected 100-mL urine samples at the start of the study and for 5 d after they had eaten each variety of potato: day 1 (basal, before eating the first potato variety), days 3–7, day 29 (baseline of the second potato variety), and days 31–35. Urine samples were collected in the morning (between 7 and 12) and stored frozen at −18°C (