Chronic kidney disease (CKD) patients who consume a diet high in vegetables rather than meat may prevent the accumulation of toxic phosphorus levels, according to a study published online Dec. 23 in the Clinical Journal of the American Society of Nephrology.Sharon M. Moe, M.D., of the Indiana University School of Medicine in Indianapolis, and colleagues conducted a crossover trial in nine patients with a mean estimated glomerular filtration rate of 32 ml/min to compare vegetarian and meat diets containing equivalent nutrients prepared by clinical research staff.
The investigators found that one week of a vegetarian diet led to lower serum phosphorus levels, decreased phosphorus excretion in the urine, and reduced fibroblast growth factor-23 levels compared with a meat diet, despite equivalent protein and phosphorus concentrations in the two diets.
“In summary, this study demonstrates that the source of protein has a significant effect on phosphorus homeostasis in patients with CKD. Therefore, dietary counseling of patients with CKD must include information on not only the amount of phosphate but also the source of protein from which the phosphate derives,” the authors write.
Cystatin C, a blood marker of kidney function, proved significantly more accurate than the standard blood marker, creatinine, in predicting serious complications of kidney disease, in a study by researchers at the San Francisco VA Medical Center and the University of California, San Francisco. Among adults who were identified as having chronic kidney disease by high creatinine levels, the researchers found that only patients who also had abnormally high levels of cystatin C were at high risk for death, cardiovascular disease, heart failure, or kidney failure. People with high creatinine but normal cystatin C levels had risks similar to those with normal creatinine levels.
The researchers also found that a small but important segment of the study population was missed by creatinine but identified by cystatin C as being at significant risk of serious complications, according to lead author Carmen A. Peralta, MD, MAS, an SFVAMC researcher and an assistant professor of medicine in residence in the division of nephrology at UCSF.
The study of 11,909 participants appears online on December 16, 2010, in the JASN Express section of the Journal of the American Society of Nephrology. The authors analyzed patient data from two prospective studies: the Multi-Ethnic Study of Atherosclerosis and the Cardiovascular Health Study, both sponsored by the National Heart, Lung, and Blood Institute.
Principal investigator Michael G. Shlipak, MD, MPH, chief of general internal medicine at SFVAMC, said that the current study highlights a potential clinical use for cystatin C as a method for confirming a diagnosis of chronic kidney disease. Shlipak has been a leader among physicians in identifying cystatin C as an alternative, accurate, and reliable marker of kidney function.
Both cystatin C and creatinine are substances made in the body and filtered by the kidneys. High levels of the substances in the blood indicate that the kidneys are losing the ability to filter them, and thus are losing function. However, explained Peralta, creatinine is a byproduct made in muscles, so it is affected by what you eat and especially by how much muscle you have. Thus, a bodybuilder with healthy kidneys might have an elevated creatinine level because of high muscle mass, whereas a frail elderly person might have normal or even low levels of creatinine, but in fact this persons kidneys are not working well – its just that theres not much creatinine because theres not much muscle.
In contrast, cystatin C is a protein made in cells throughout the body. In studies so far, it does not seem to be that affected by age or muscle mass or diet, said Shlipak, who is also a professor in residence of medicine and epidemiology and biostatistics at UCSF.
Shlipak proposes that cystatin C, which can cost as little as $17 per test, be added as a method for confirming or staging chronic kidney disease in guidelines that are currently being formulated by nephrologists. Its vital that we have an accurate diagnostic test, because kidney disease does not show symptoms until its too late, when your kidneys have almost failed completely, he said. Being missed by creatinine is an important limitation in our current method of diagnosing kidney disease, said Peralta. Yet, she adds, being falsely identified with kidney disease through inaccurate test results can be disastrous as well. There is fear and psychological stress, particularly in communities of color, where people have a lot of friends and family members who are on dialysis, she noted. You can also be subjected to unnecessary and expensive tests and medications.
In previous research, scientists using information collected from the National Health and Nutrition Examination Survey (NHANES), a long-term collection of studies designed to assess the health and nutritional status of adults and children in the US, had found a link between sugar containing sodas and urinary protein. However, they did not collect data on any kidney function changes related to drinking sweetened sodas. So, in their second study, Dr. Lin and Dr. Curhan, decided to specifically check for any kidney function decline in women who drink sodas regularly. Once again, they used data from the Nurses' Health Study.
In a statement for the media, Dr. Lin reported they found “a significant two-fold increased odds, between two or more servings per day of artificially sweetened soda and faster kidney function decline; no relation between sugar-sweetened beverages and kidney function decline was noted.” Moreover, this association persisted even when the researchers accounted for age, obesity, high blood pressure, cardiovascular disease, physical activity, calorie intake, diabetes and cigarette smoking. Clearly, artificially sweetened sodas are detrimental to kidney health.
“There are currently limited data on the role of diet in kidney disease,” said Dr. Lin in a statement to the press. “While more study is needed, our research suggests that higher sodium and artificially sweetened soda intake are associated with greater rate of decline in kidney function.”
Kidney stones are small, hard deposits of minerals and salts that can form in the kidneys when urine becomes concentrated. Specific treatment beyond increasing water intake is usually not needed, but a kidney stone can be very painful to pass, as anyone who has had one can tell you. While anyone can get kidney stones, there are multiple risk factors that can potentially increase your chances of acquiring them, including:
- Family history of kidney stones.
- Being over 40 years old.
- Being male.
- High protein, high sodium and high sugar diets.
- Being obese.
- Digestive diseases such as inflammatory bowel disease or surgeries such as gastric bypass.
You can reduce your risk of getting kidney stones by:
- Drinking water throughout the day. For those with a history of kidney stones, doctors usually recommend passing approximately 2.5 litres of urine daily. In summer months you need to consume considerably more fluids to stay well-hydrated.
- Eating fewer foods containing high amounts of oxalate. Kidney stones can form due to a build up of calcium oxalate. Foods rich in oxalate include spinach, beets, rhubarb, okra, tea, chocolate and soy products.
- Limiting salt and animal protein in your diet. Reduce the amount of salt in your diet and choose non-animal protein sources such as nuts to reduce your chances of getting kidney stones.
- Watching out for stealth sources of sodium. Some energy and sports drinks contain high levels of sodium and/or caffeine. While they may quench your thirst, you may also be increasing your risk of stone formation.
- Re-hydrating often if engaged in strenuous activity if you have long-term exposure to the heat. Painters, roofers, landscapers, marathon runners and people who enjoy outdoor sports activities that last several hours at a time need to pay special attention to their water intake and watch for signs of dehydration. Health experts recommend at least 16 to 32 ounces of water per hour of heat exposure. A lack of sweat or urination, dizziness, weakness, headache, muscle cramps, nausea or vomiting are possible signs of heat-related illness or dehydration.
- Avoiding calcium supplements, but calcium-rich foods are OK. Calcium in the food you eat does not increase your risk of getting kidney stones. Keep eating calcium-rich foods unless your doctor advises you otherwise. However, calcium supplements have been linked to higher risk of kidney stones. Consult your physician before starting a calcium supplement.
A dietitian like Nastaran can help those at risk to plan meals that will reduce the chance of getting kidney stones.