A very low protein diet with amino acid supplements may cure a severe kidney disease in some people, a Johns Hopkins study shows. The results suggest the dietary therapy should be tried before drug treatment for nephrotic syndrome, a chronic kidney disorder that often leads to kidney failure.
Scientists have not solved the paradox of why eating less protein benefits some patients -- sufferers already lose too much protein in their urine, yet restricting dietary protein may help many sufferers, says Mackenzie Walser, M.D., the study's lead author and a professor of pharmacology, molecular sciences and medicine. The study, which was supported in part by the National Institutes of Health, is published in the September issue of the American Journal of Kidney Diseases.
"Five patients remain virtually cured, while only one patient's blood-protein level worsened, " says Walser.
Hopkins researchers put 16 adults on a very low protein diet with essential amino acid or ketoacid supplements for 10 months. Essential amino acids are those amino acids -- building blocks of protein -- that the body can not make. Ketoacids are slightly modified forms of amino acids.
The disorder gradually disappeared during the next three to 15 months in five participants, who started the study before kidney failure became severe, the results show. Four of the five people have resumed normal or nearly normal diets and have remained in remission or near remission for six months to two years. The other 11 participants, who had more advanced kidney failure before starting the study, showed temporary improvement, but all eventually went on dialysis.
Nephrotic syndrome usually is treated with drugs and only modest reduction of dietary protein to reduce the loss of protein in the urine. Severe protein restriction has been avoided for fear of aggravating the low levels of protein in the blood.
In contrast with other treatments, such as steroids or immunosuppressive drugs, the dietary treatment, though often difficult for patients to follow, has no side effects, says Walser. The diet excluded such high-protein foods as meat, fish, poultry, cheese and milk and included supplemental tablets of amino acids, the building blocks of protein.
"We still don't know the mechanism for this surprising result," says Walser. "Evidently, some unidentified component of a regular diet was perpetuating the loss of urinary protein. What's clear from our findings is that the common opinion that kidney disease patients shouldn't be given severely protein-restricted diets needs to be reconsidered."
Hopkins researchers plan to repeat the study with a larger number of patients.
Nephrotic syndrome is marked by damage to the glomeruli, the kidney's filtering units. This causes severe loss of protein from the blood into the urine, severe fluid retention and extremely high blood cholesterol. The syndrome may result from diabetes mellitus, severe high blood pressure or other causes and often leads to the need for dialysis or transplantation.
Previous Hopkins studies have shown that a very low protein diet before dialysis may prolong the lives of some kidney failure patients after they start dialysis and may postpone the start of dialysis for others.
The current study's other authors were Sylvia Hill, B.S. and Elizabeth A. Tomalis, M.P.H.