Magnesium and zinc status in patients with chronic renal failure: influence of a nutritional intervention

Chronic renal failure (CRF) alters the metabolism for a number of elements, and can lead to deficiency of these nutrients. Among the causes of these alterations are reduced food intake and the low element content of some low-protein diets recommended in CRF. This study aimed to determine whether nutritional status for magnesium and zinc were changed by a nutritional intervention providing patients with CRF with enough information to prepare a low protein diet that met their needs. The effects of the intervention were compared in 40 adult participants divided into two groups. The control group consumed their usual prescribed diet, and the nutritionally instructed group received dietary training to teach them how to choose foods that met their nutritional needs. The study period lasted 12 months. Food consumption was assessed by 24-h recall. Magnesium and zinc were measured in plasma at the start and at the end of the study. Participants in the nutritionally instructed group decreased their protein intake and increased that of carbohydrates, magnesium and zinc. Plasma zinc correlated with glomerular filtration rate, measured as creatinine clearance, (r = 0.37) plasma protein (r = 0.39) and zinc intake (r = 0.63). At the start of the study 1 participant in the control group and no participants in the instructed group had hypomagnesaemia (< 1.8 mg/dL) whereas 2 participants in the control group, and 5 in the instructed group had hypozincaemia (Zn < 70 mu g/dL). After the intervention we observed no changes in the number of participants with hypomagnesaemia in either group, whereas hypozincaemia was found in only 1 participant in the control group and 1 in the instructed group (changes in the instructed group were significant; p < 0.05). Nutritional intervention benefited our participants by improving their ability to choose foods that provided magnesium and zinc while reducing their protein intake. The results of this study indicate that the dietary intervention enabled participants to better control their protein intake and zinc status without detriment to magnesium status.