Screening and study procedures
In response to advertisements, people expressing an interest in the study were provided with further information (Participant Information Sheet) and their potential involvement was discussed with a member of the study team. Participants who remained interested in taking part in the study were asked to complete and sign the consent form.Once informed consent had been obtained, the body height and weight of the participants were measured using standardized equipment and the BMI was calculated to determine if participants were eligible for the study. Venous blood samples (∼3 mL in a Vacutainer SST II Advances Tubes—with an inert gel barrier, and 3 mL in a K-EDTA Vacuum tube) were taken and used to measure high-sensitivity CRP (Turbidimetry, Vitros 4600—Ortho Clinical Diagnostics) and hemoglobin (5-part differential flow, Nihon Kohden), respectively. The tubes with the inert gel barrier were centrifuged and 0.5-mL aliquots of serum were transferred into cryovials. All samples were stored at <18°C until analysis. A 30-mL urine sample was collected from all candidates as part of screening to rule out pregnancy. According to the results of screening, and after checking that they complied with all the selection criteria, they were invited to participate in the study.Women were randomly allocated to start the study with one of the varieties of potato (biofortified, meal A, or regular potato, meal B). Each type of potato had a group code so that the participants were blinded to the variety they received. A list of random numbers was prepared in Excel to establish the order of assignment to each participant. This list was drawn up before the start of the trial.All the participants were given both types of potato in a random order, thus each participant acted as their own control. The first variety of potatoes was given on day 1 and the second on day 29. All meals were consumed alone, without other food, with drinking water. Participants were allowed to add salt to their meals to their liking. The subjects consumed 1000-g potato in 2 meals of 500 g administered on 2 separate occasions within the day, as giving the whole quantity in 1 meal would be unacceptable to most participants. The first meal was given in the morning after an overnight fast (≥8 h without food and 6 h without any drink) and in 2 portions (250 g each). When they had eaten the first half of the meal, depending on the potato variety that they had been allocated, they received 0.25-mg 