Fruit and vegetable intake to correct metabolic acidosis in CKD

CKD Managementmedium

A 55-year-old man with CKD stage 4 attributed to type 2 diabetes and hypertension presents for follow-up. The patient reports feeling well. He is adherent to his medication regimen, which includes lisinopril, glipizide, and atorvastatin. At his last visit 6 months ago, the patient was reluctant to add any new medications but was agreeable to dietary changes. His BP is 125/75 mm Hg, and he has no peripheral edema. The remainder of the physical exam is normal. Laboratory data (6 months ago; current): potassium 4.2 mEq/L; 5.0 mEq/L (reference 3.5–5.0); total CO₂ 16 mEq/L; 19 mEq/L (23–28); creatinine 2.10 mg/dL; 2.0 mg/dL (0.7–1.3); BUN 14 mg/dL; 15 mg/dL (8–20); phosphorus 3.5 mg/dL; 3.3 mg/dL (3.0–4.5); hemoglobin A1c 7.5%; 7.2% (4.0–5.6). Increased dietary intake of which of the following MOST LIKELY accounts for the observed changes?

  1. A.Fish
  2. B.Dairy
  3. C.Fruits and vegetablesCorrect
  4. D.Whole grains

Explanation

This patient's most likely dietary change is an increase in his consumption of fruits and vegetables. Metabolic acidosis is a common complication of CKD, and alkali therapy is often prescribed to correct this acidosis. Various studies have examined dietary modifications in patients with CKD; plant-based diets are being investigated for improving CKD outcomes. In one study, increased consumption of fruits and vegetables significantly improved serum bicarbonate levels, though to a lesser degree than sodium bicarbonate supplementation. Of note, sodium bicarbonate supplementation to improve serum bicarbonate has been shown to delay the progression of CKD. Fruits and vegetables are often high in potassium, so monitoring for hyperkalemia is imperative, particularly in patients taking ACEIs. The increase in serum bicarbonate and potassium suggest that the patient has increased his intake of fruits and vegetables. Grains, dairy, and animal protein (such as fish) are all associated with an acid load. In addition, these foods are relatively rich in protein and phosphorus, which would be expected to result in increased BUN and phosphorus concentrations. Increased intake of these foods would be unlikely to cause the improved total CO₂ and stable BUN and phosphorus levels observed in this case.

Why each option

A.
Fish is animal protein that generates sulfuric acid from amino acids and adds phosphorus and urea, lowering rather than raising bicarbonate.
B.
Dairy adds protein and a large phosphorus load with net acid generation, which would raise BUN and phosphorus rather than correct acidosis.
C.
Correct. Fruits and vegetables supply organic anions metabolized to bicarbonate and are potassium-rich, explaining higher total CO₂ and potassium with stable BUN.
D.
Grains generate a net acid load and add protein and phosphorus, so they would not raise total CO₂ or potassium as seen.

Reference: Goraya N, Clin J Am Soc Nephrol 2013 (fruits and vegetables versus bicarbonate in CKD stage 4); Ikizler TA, Am J Kidney Dis 2020 (KDOQI clinical practice guideline for nutrition in CKD: 2020 update)

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