Image 2 — The kidneys, ureters, and bladder, showing the structures involved in urinary stone disease.
Chapter 3: Why Kidney Stones Develop and Who Faces a Higher Risk
Urinary stones do not usually form because of one isolated mistake. Their development reflects a combination of urine chemistry, fluid intake, diet, genetics, anatomy, medical conditions, and sometimes infection. Understanding these influences is essential because a person who has already developed a stone may face a significant risk of developing another one.
The most effective prevention strategy depends on identifying the factors that matter for the individual rather than following a universal list of dietary restrictions.
Dehydration and concentrated urine
One of the most important contributors to stone formation is urine that becomes too concentrated. When the body does not receive enough fluid, or when it loses substantial amounts through sweating, vomiting, diarrhea, or other processes, the kidneys conserve water and produce more concentrated urine.
In concentrated urine, certain minerals and compounds can reach levels that favor crystal formation. If crystals grow or accumulate rather than remaining dissolved, a stone may eventually develop.
People who work outdoors in hot conditions, exercise intensely, spend long periods in high temperatures, or have limited access to drinking water may face additional challenges maintaining hydration. Those who repeatedly become dehydrated may have an increased likelihood of stone formation, particularly when other risk factors are present.
However, fluid needs differ between individuals. Body size, climate, physical activity, pregnancy, medication, and underlying health conditions all influence requirements. People with heart failure, advanced kidney disease, or certain other medical conditions may have prescribed fluid restrictions and should not increase their intake without medical advice.
For many people who have developed stones, clinicians recommend sufficient fluid intake to produce a generous volume of urine. Prevention plans often use a target of approximately 2 to 2.5 liters of urine per day, although the appropriate goal depends on individual circumstances and may require drinking more than that volume in fluids.
The distinction between urine output and the amount consumed matters. Some fluid is lost through sweat and breathing, so the volume a person needs to drink is not identical to the volume of urine they produce.
Calcium oxalate: A common type of urinary stone
Calcium oxalate stones are among the most common forms of kidney stones. They develop when calcium and oxalate in urine combine under conditions that favor crystal formation.
Oxalate occurs naturally in many foods, including certain nuts, seeds, leafy vegetables, and other plant products. Calcium is found in dairy foods and various other foods. The relationship between these nutrients is more complicated than simply avoiding every food that contains oxalate or calcium.
In fact, severely restricting dietary calcium can increase the risk of calcium oxalate stones in some people. Calcium consumed with food can bind oxalate in the digestive tract, reducing the amount absorbed into the bloodstream and later excreted in urine.
For this reason, many people with calcium oxalate stones are advised to maintain an appropriate intake of dietary calcium rather than eliminate it. The amount should be consistent with age, health status, and clinical recommendations.
Some people may benefit from moderating foods that are particularly high in oxalate, especially when urine testing suggests that oxalate excretion is elevated. However, a highly restrictive diet is not necessary or appropriate for every patient.
The better approach is to examine the full dietary pattern, including fluid intake, sodium consumption, calcium intake, and the individual's stone composition.
Too much sodium can increase urinary calcium
Sodium is another important factor. A high-sodium diet can increase the amount of calcium excreted in urine, potentially contributing to calcium stone formation in susceptible individuals.
Many people consume more sodium than they realize because it is present in processed foods, packaged snacks, cured meats, instant meals, restaurant dishes, and sauces. The problem is not limited to the salt shaker on the dining table.
Reducing excessive sodium intake may help lower stone risk while also supporting cardiovascular health. Practical measures include cooking more meals at home, comparing nutrition labels, choosing less heavily processed foods, and using herbs or spices to add flavor.
People do not need to eliminate sodium entirely. The body requires sodium for normal physiological function, and needs can vary with medical conditions and activity. The goal is to avoid excessive intake and follow appropriate dietary guidance.
Animal protein and uric acid stones
Dietary patterns high in certain animal proteins can affect urinary chemistry. Purines, compounds found in various foods and produced naturally by the body, are broken down into uric acid.
High uric acid levels and persistently acidic urine can promote uric acid stone formation. Excessive intake of certain meats and organ meats may be relevant for some people, particularly those with gout or other metabolic risk factors.
However, protein is an essential nutrient, and eliminating it is not the answer. The appropriate amount and sources of protein depend on nutritional needs, kidney function, and stone composition.
A balanced dietary pattern may include appropriate portions of plant proteins, fish, poultry, and other protein sources. People with recurrent uric acid stones may need a more individualized plan based on urine testing and blood results.
In selected patients, medication can help alter urinary chemistry and reduce the likelihood of uric acid stone formation.
Genetics and family history
Some people develop stones despite maintaining good hydration and following a balanced diet. Genetic factors can influence how the body absorbs, processes, and excretes minerals.
A family history of kidney stones is associated with an increased likelihood of developing them. In some cases, inherited disorders can cause unusually high levels of particular substances in urine or interfere with normal kidney function.
Cystinuria is one example. This inherited condition causes excess cystine, an amino acid, to appear in urine. Cystine can crystallize and form stones, sometimes beginning at a relatively young age and recurring throughout life.
Other metabolic conditions can also contribute to recurrent stone formation. When stones develop repeatedly, occur at a young age, appear in both kidneys, or are unusually difficult to treat, clinicians may consider a more detailed metabolic evaluation.
Family history does not mean that stone formation is inevitable. It does mean that prevention and follow-up may deserve additional attention.
Medical conditions and medications
Certain health conditions increase stone risk. These include some metabolic disorders, gout, disorders affecting calcium regulation, chronic diarrhea, and conditions that change urinary acidity or composition.
People who have undergone certain types of gastrointestinal surgery or who have diseases that affect intestinal absorption may absorb more oxalate, increasing the risk of calcium oxalate stones.
Some medications and supplements can also influence stone formation. The effects depend on the substance, dose, and the person's health status. High doses of certain supplements may be inappropriate for people who are already susceptible to stones.
Patients should not stop prescribed medication simply because they read that it may be associated with stone formation. A clinician can assess the risk and determine whether an alternative or monitoring is needed.