Effect of boiling on dietary phosphate and nitrogen intake

Objective: Dietary phosphate restriction is one of the means of phosphatemia control in dialysis patients. To limit dietary phosphate intake, appropriate food choices are recommended, but this often creates a conflict with the high-normal protein requirement of dialysis patients. Although food processing by boiling may be a safe tool for eliminating many minerals, this method poses a risk for loss of important nutrients, including proteins. The goal of this study was to assess the effect of boiling on phosphate and protein nitrogen changes in commonly used foods that contain proteins of high biological value. Methods: We evaluated the true retention values of dry matter, crude protein, and total phosphorus in fresh beef and chicken breast before and after 10, 20, and 30 minutes of boiling; the reported values represent the average of five determinations. Results: Compared with crude raw samples, dry matter retention in cooked beef was reduced up to 92% +/- 6%, crude protein retention was reduced up to 87% +/- 10%, and phosphorous retention was reduced up to 42% +/- 13%; similar data were obtained when boiling the chicken breast, 93% +/- 3%, 81% +/- 4%, and 63% +/- 6%, respectively. Conclusions: Our results show that consuming boiled foods can significantly reduce dietary phosphate while preserving protein intake, namely reducing the effective phosphate intake per gram of dietary protein. This can represent additional advice to the patient for limiting the dietary phosphorus load at the same protein intake, leading to a better control of phosphate balance together with a lower risk of protein malnutrition. (c) 2006 by the National Kidney Foundation, Inc.