Metabolic Acidosis: Nutritional Management Suggests Multiple Benefits for CKD Patients
Contemporary treatment of chronic kidney disease (CKD) involves a holistic approach that recognizes nutrition as a powerful tool in deterring disease progression, preventing comorbidities and enhancing overall patient well-being. In line with this is the movement toward nutritional management of metabolic acidosis. Studies show that a diet dense in alkaline-producing foods can be effective in treating metabolic acidosis while providing additional benefits as well.
As part of the body’s excretory system, the kidneys play a critical role in maintaining the blood’s acid-base balance by excreting nonvolatile acids and reabsorbing bicarbonate in the kidney tubules. In CKD patients, the renal system’s inability to properly adjust the blood’s narrow pH (7.35 to 7.45) by proton excretion and bicarbonate filtration results in inadequate rates of acid excretion and alkali reabsorption. This failure to neutralize the acid load per normal function leads to leeching necessary elements from other sources, such as calcium from bone and glutamine from muscle. When key minerals are depleted throughout the body, the following complications can ensue1-7:
- Increased protein catabolism
- Mineral and bone disorders
- Muscle wasting
- Chronic inflammation
- Impaired glucose homeostasis
- Impaired cardiac function
- Progression of CKD
- Increased mortality
How significant is the issue of metabolic acidosis in CKD patients? As kidney disease progresses, the occurrence of metabolic acidosis increases. By stage 3, 2.3 to 13 percent of CKD patients present with metabolic acidosis, and by stage 4, the occurrence escalates to 19 to 37 percent.8-9 Our modern diet, consisting largely of foods that produce a high acid load (i.e., high in sulfur-containing amino acids that are metabolized toward sulfuric acid) and lacking in those that buffer acid, exacerbates metabolic acidosis. For perspective, considering a score of zero as a neutral load, pre-industrialized diets produced -88 mEq/L (resulting in more alkaline excretion) while modern diets produce +47 mEq/L (resulting in more acid excretion).
The key elements in an alkaline diet include the reduction of animal protein (consumed through meat, fish and diary), whole grains, soft drinks and artificial sweeteners, while increasing fruit and vegetable consumption, which produces alkali and neutralizes acid. (Note: Some foods have a neutral affect, such as oils, nuts and seeds).10-12 The lower-protein diet—with increased fruits, vegetables, legumes, soy protein and egg whites as the limited protein sources—not only lowers net acid production, reducing the acid load to be managed by the kidneys, but alters gut flora to potentially produce more short chain fatty acids (alkali) and slow the production of nephrotoxic substances.
Traditionally, the standard treatment to offset the acid load is oral sodium bicarbonate supplementation,13-14 which has shown to be beneficial in slowing disease progression.15-17 However, nutritional management has shown to not only slow disease progression but reduce blood pressure as well. Furthermore, studies suggest an alkaline diet introduced before evidence of metabolic acidosis appears may help stage 3 patients as a means of prevention. In light of these findings, along with that of patients reporting feeling better, nutritional management of metabolic acidosis has gained attention as an alternative treatment to sodium bicarbonate supplementation.
Prescribing an alkaline diet can be challenging. Exact recommendations for dietary reductions and increases must be based on multiple factors, including individual stage of disease, nutrition status and body size. On the patient side, successful adoption of the alkaline diet requires commitment and engagement with his/her own health management. Therefore, not all patients will be ideal candidates. For those who are, dietary manipulation can be an appealing method for metabolic acidosis management, delaying renal disease progression, improving comorbidities, alleviating related complications and aiding in overall well-being.