What Causes Kidney Stones?

Stones (calculi) are solid, crystalline masses that can form in various parts of the human body—most commonly in the kidneys, ureters, gallbladder, or bladder. Small or few stones may cause no noticeable symptoms. However, larger stones can trigger pain, bleeding, and even secondary infections. Stone disease significantly impacts quality of life and overall health. Many people are concerned about the underlying causes of stone formation and wish to prevent it. So, how do stones develop? Let’s explore the key contributing factors.

What Causes Stone Formation?

1. Excessive Fat Intake

Meats—especially fatty pork—are high-fat foods. Overconsumption elevates bodily fat levels, which reduces intestinal calcium availability for binding. This, in turn, increases oxalate absorption. Most people are unaware of how kidney stones develop; however, if urinary excretion is impaired—for example, due to excessive sweating, inadequate fluid intake, or low urine output—kidney stones are highly likely to form.

2. Abnormal Purine Metabolism

Organ meats, seafood, peanuts, green beans, spinach, and other foods contain high levels of purines. Once ingested, purines undergo metabolism, ultimately producing uric acid. Elevated uric acid promotes precipitation of calcium oxalate in urine. Consuming large amounts of purine-rich foods—particularly when purine metabolism is already impaired—can lead to oxalate deposition in urine and subsequent stone formation.

3. Elevated Sugar Intake

Sugar is an essential nutrient requiring regular, moderate supplementation. Yet sudden, excessive intake—especially of lactose—creates favorable conditions for stone formation. In both healthy individuals and stone-formers, consuming 100 g of sucrose leads to increased urinary calcium and oxalate concentrations within two hours. Lactose further enhances calcium absorption, thereby promoting calcium oxalate accumulation and increasing the risk of urinary stone formation.

4. Excessive Oxalate Accumulation

Excessive endogenous oxalate accumulation is one major contributor to kidney and urinary stones. Commonly consumed foods—including spinach, legumes, grapes, cocoa, tea, oranges, tomatoes, potatoes, plums, and bamboo shoots—are notably rich in oxalates.

5. Excessive Protein Intake

Chemical analysis of kidney stones reveals that calcium oxalate constitutes approximately 87.5% of their composition. This high proportion stems partly from dietary protein, which supplies glycine and hydroxyproline—the precursors of oxalate—and also enhances intestinal calcium absorption.

Knowledge Extension: Who Is at Higher Risk for Stone Formation?

1. Individuals with a family history of kidney stones: If your first-degree relatives have had kidney stones, your personal risk is significantly elevated.

2. Sedentary individuals: Prolonged physical inactivity not only impairs calcium absorption but also increases urinary calcium excretion—raising the risk of kidney or urinary tract stones.

3. People with a preference for salty, high-protein diets: Diets high in protein, sodium, and sugar may increase the risk of certain stone types—especially sodium-rich diets, as excess dietary sodium elevates renal calcium levels. Therefore, avoid overly salty foods.

4. Individuals who skip breakfast: Without morning food intake, the gallbladder lacks stimulation to release bile, causing prolonged bile stasis. Over time, this stagnation predisposes to gallstone formation.

The above outlines the primary causes of stone formation. We hope this information proves helpful to you.