Doctors were shocked to find approximately 420 stones from a man's kidney in China. The 55-year-old man, named He Dong, underwent a surgical operation that lasted for two hours at a medical facility in Dongyang, eastern Zhejiang Province.

The doctors who removed the stones said the reason for such a high number of impurities may be due to the man's tofu addiction and minimal water intake.

He Dong first consulted a doctor in May after experiencing severe abdominal pain. A computed tomography (CT) scan revealed that the patient had a stone-packed kidney. The medical team then recommended immediate surgery to remove the stones as the patient had reached the point at which he could no longer pass water. Delaying the operation would have necessitated the complete removal of his kidney.

"I have never seen so many stones before. The operation took less than two hours of which 45 minutes was used to remove the stones," said Dr Wei Yubin, a surgeon who operated on He Dong. "At the end of the operation I realized my arms and legs were numb. The plate used to collect the stones had at least 420 of them of varying sizes and colored green and yellow."

That number does not include the extremely tiny stones obtained through a special suctioned machine utilized during the operation. Based on estimates, more than 100 more stones were collected by the said equipment.

He Dong, a manual laborer, said he frequently eats high amounts of a local street food called gypsum tofu but is not fond of drinking water. This main component of He Dong's diet contains a large concentration of calcium sulphate.

"Soy products, especially gypsum tofu, are very high in calcium, the excess of which cannot be excreted from body without a sufficient intake of water," explained Dr Wei.

He Dong was treated 20 years ago for the same type of pain and diagnosis. He was then found to have 10 kidney stones. He underwent a non-invasive procedure called lithotripsy, which is a shockwave therapy that breaks down kidney stones to small pieces so the patient can excrete them through urine. The symptoms recurred two years ago but it was only during these past two months that the pain became extreme and he could no longer perform his daily activities.

His family says they will ensure he does not eat tofu in the same way he has been in the past.