Boiling sliced meat in a pressure cooker containing soft water and then discarding the cooking liquid may provide a good way for dialysis patients to reduce phosphorus levels while maintaining adequate protein intake, a new study suggests.
Masae Sakuma, PhD, and colleagues from the University of Shizuoka in Japan, assessed the phosphorus and protein content of beef cooked in a variety of ways. They cut beef in 100 gram blocks, cubes, or slices (i.e., muscle fibers cut vertically). They used different cooking liquids, including soft bottled water, hard water, 5% acetate solution (i.e., a mixture of soft water and vinegar), and 0.5% sodium bicarbonate water (i.e., a mixture of soft water and sodium bicarbonate). They cooked the beef either in a regular pan or pressure cooker for 10 or 30 minutes.
According to results published online ahead of print by the Journal of Renal Nutrition, certain methods decreased the phosphorus content of the meat the most. Soft water was the best cooking liquid, probably due to preferential osmotic pressure. Sliced meat appeared to provide a large surface area for phosphorus to exit. Likewise, pressure cookers, which allow cooking at a higher temperature and pressure, allowed the muscle fibers in meat to flex easily so phosphorus flowed readily. Since phosphorus leaches into the cooking liquid, the liquid must be discarded. Based on previous research, the investigators further suggested that boiling meat is more effective at reducing phosphorus than pre-soaking it.
Importantly, the protein content of the meat stayed the same. “The dissociation between phosphorus and protein is possible because boiling may easily influence the discharge of phosphorus from the intercellular and extracellular spaces and from the phospholipids of cell membranes, whereas proteins remain within the cells and are not lost in the boiling fluids,” the investigators explained.
The cooking advice is particularly valuable for dialysis patients who need to avoid protein-energy malnutrition. Rather than consume only low phosphorus foods, which tend to be low in protein, they can cook meat to lower phosphorus while retaining protein. The National Kidney Foundation Kidney Disease Outcomes Quantity Initiative guidelines recommend a daily phosphorus intake of 10 to 12 mg per gram of protein.