A review of randomized control trials demonstrated that dietary fiber supplementation reduced the levels of uremic toxins in patients with kidney disease, most notably for those who received dialysis or who did not also have diabetes.
“Uremic toxins are substances that accumulate in the body after kidney function declines, which is a risk factor associated with cardiovascular disease, progression of kidney dysfunction, mineral bone disorders, and increased mortality in patients with chronic kidney disease (CKD),” Hui-Li Yang, BSN, of the school of nursing at Medical College of Soochow University, Suzhou, People’s Republic of China, and colleagues wrote. “Indoxyl sulfate (IS) and p-cresyl sulfate (PCS) are protein-bound uremic toxins derived by bacteria in the large intestine that are currently receiving much attention.”
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According to the researchers, the levels of these toxins are 54% and 17% higher in patients on dialysis vs. the general population and only 30% of these toxins can be removed during hemodialysis treatments.
In addition, the researchers pointed to other uremic toxins (such as uric acid, blood urea nitrogen and creatinine), which they noted are small molecule toxins and can easily be removed by dialysis. However, they argued that because these levels are still high before dialysis, it is necessary to find methods to reduce these in patients who have not yet progressed to kidney failure.
To investigate the role dietary fiber supplementation might play, Yang and colleagues reviewed 10 studies, 70% of which were deemed “high quality” (ie, received a methodological quality score of at least 8). In total, the studies involved 292 individuals, with researchers noting that while studies were conducted primarily in Asian countries, three were conducted in American countries and one in Europe. All studies included details on type and dosage of dietary fiber (resistant starch was most commonly used; doses ranged from 90 mL per day to 25 g per day).
After calculating the standardized mean difference in uremic toxin levels after the intervention period in each study, researchers found fiber supplementation significantly reduced the levels of indoxyl sulfate (standardized mean difference [SMD] = -0.55), p-cresyl sulfate (SMD = -0.47), blood urea nitrogen (SMD = -0.31) and uric acid (SMD = -0.60). No reductions were seen for creatinine.
Further findings indicated that patients who received dialysis saw greater reductions in uremic toxins with supplementation than those with CKD, while patients without diabetes had greater reductions than those with diabetes.
“The accumulation of uremic toxins was more serious in patients with end-stage renal disease; therefore, the higher baseline uremic toxin levels in patients on dialysis are [easier] to reduce, which may be the reason for more reduction of uremic toxins in this subgroup,” Yang and colleagues theorized. “As for the more obvious effect in the subgroup of patients without diabetes compared to patients with diabetes, the reason may be the side effect of specific dietary regimen for diabetes patients.”
This finding, according to the researchers, suggests that dialysis and diabetes are “influential factors” on the potential effect of dietary fiber supplementation and should be assessed in future studies.
Despite some acknowledged limitations, the researchers concluded that “supplemental dietary fiber can be used as an auxiliary method to reduce uremic toxins in patients with CKD in clinical practice.”