Spinach contains high levels of oxalic acid, one of the main components in the formation of calcium oxalate stones — the most common type of kidney stone.

Man develops kidney disease due to oxalate deposition

Mr. Tran (42, China), who had been generally healthy except for mild, untreated gout, began experiencing persistent fatigue, drowsiness, and frequent bowel movements (4–5 times a day) about a week ago. When he went to the hospital, test results shocked his family: his blood creatinine level had risen to 430 μmol/L (many times higher than normal), and an abdominal CT scan revealed multiple abnormalities in his kidneys.

After further tests, doctors diagnosed him with kidney disease caused by oxalate deposition. This condition occurs when calcium oxalate crystals accumulate in the renal tubules, damaging kidney tissue and impairing function.

Surprisingly, the “culprit” behind the 42-year-old man’s hospitalization was spinach, a vegetable loved by many Vietnamese people.

Root cause: overeating spinach


Doctors discovered that Mr. Tran had eaten spinach continuously for several days prior to his illness. Spinach is high in oxalic acid, and when combined with his prolonged diarrhea — which altered absorption and excretion processes — it triggered acute kidney injury.

Fortunately, after timely treatment with IV fluids, diuretics, calcium supplementation, and kidney-protective therapies, his condition improved significantly, and his creatinine levels returned close to normal.

Doctors explained that oxalate in the body is primarily excreted by the kidneys through urine. When oxalate levels become abnormally high, they bind with calcium to form calcium oxalate crystals — like tiny “shards of glass” that scratch and block the renal tubules, creating stones and gradually destroying kidney function. Without treatment, this condition can progress to chronic kidney failure, requiring dialysis or even a transplant.

---

4 “Healthy” Foods Kidney Patients Should Avoid Eating Too Often

1. Spinach and kale

These leafy greens are rich in vitamins, minerals, and antioxidants. However, spinach and kale are also high in oxalate, a main component of calcium oxalate kidney stones. Overconsumption increases the risk of stones, especially if you don’t drink enough water.

Prof. William E. Mitch, a nephrology expert at Baylor College of Medicine (USA), noted: “Not all foods that are healthy for the general population are suitable for kidney patients. Balance in diet is essential, and patients should always consult a doctor or nutritionist, particularly if they have underlying conditions.”

2. Soybeans and soy-based products

Soy is rich in plant protein, beneficial for heart health and cholesterol reduction. However, in chronic kidney disease patients, high protein intake from soy can burden the kidneys, increasing blood urea and creatinine levels. In addition, soy contains oxalate, which can crystallize into kidney stones when accumulated.

3. Bananas

Bananas are a natural source of potassium, supporting heart and muscle function. But in kidney disease, impaired kidneys cannot excrete potassium effectively, leading to hyperkalemia — a condition that can cause arrhythmias and even sudden death. Because bananas are high in potassium, excessive intake is dangerous for kidney patients.

4. Coconut water

This natural beverage helps with hydration and electrolyte replenishment, and it benefits heart health. However, coconut water is also rich in potassium. Like bananas, it can cause abnormally high potassium levels in kidney patients. Excessive consumption may also lead to electrolyte imbalances, swelling, or high blood pressure.