A single-patient case study raises concerns about the carnivore diet’s impact on kidney stone risk—does cutting out plants do more harm than good?
Case Study: You are what you eat—should it be all meat?: Impact of the carnivore diet on the risk of kidney stone development. Image Credit: Video_Stock _Production / Shutterstock
In a recent article in The American Journal of Clinical Nutrition, researchers presented the case of a person with kidney stones to discuss the best nutrition-related practices that should be followed in such cases. They discussed the possible long-term risks of fad diets, such as the carnivore diet, which lack scientific evidence and may contribute to metabolic imbalances that increase kidney stone risk.
Description of the Case
The patient, a 61-year-old man, initially sought medical assistance because he had a personal and paternal family history of kidney stones, gout, hypertension, coronary artery disease, and diabetes. His first stone developed when he was 45, after which he was asymptomatic until 55. However, from that time until he was 58, he passed approximately three stones each year, with them becoming more painful and difficult to pass over time.
He was given shock wave treatments until his kidneys could no longer tolerate them. He had undergone nine lithotripsies and was informed that further procedures could not be performed. He was also occasionally prescribed oxycodone to facilitate the passage of stones.
When analyzed, the stones were 10% calcium phosphate and 90% calcium oxalate. Laboratory studies suggested that he drank an adequate amount of fluids and that his citrate levels were normal. However, his calcium, sodium, oxalate, and uric acid levels were high, as were his supersaturation levels for calcium phosphate and oxalate. Despite his good fluid intake (urine volume of approximately 3 liters daily), his urine supersaturation for calcium oxalate and calcium phosphate exceeded safe thresholds. A computed tomography (CT) scan revealed several small stones.
For the next two years, the patient continued to pass stones; another analysis found that the stones now comprised calcium phosphate, calcium oxalate, and 10% uric acid. During this period, he developed gout and high blood pressure, both of which were treated with medication. For three years, until age 67, he did not pass any more stones, and laboratory tests found normal levels of uric acid, pH, oxalate, and calcium in his urine.
The patient changed his diet to a 90% meat-based diet after watching a popular YouTube video advocating for the carnivore diet as a gout treatment. This recommendation was not evidence-based and conflicted with established dietary guidelines for gout and kidney stone prevention. A subsequent urine test found that although risk factors for stones improved, some worsened, including a significant increase in urine calcium and uric acid levels.
By age 68, he had stopped following a carnivore diet, had no more stones, and did not experience any urological symptoms. Although some stone risk factors decreased after stopping the diet, his urine citrate, urine urea nitrogen (UUN), and protein catabolic rate (PCR)—all of which influence kidney stone risk—remained high.
Kidney Stone Formation
Supersaturation occurs when the minerals in urine exceed their solubility; this contributes to stone formation. High supersaturation increases the likelihood of kidney stone formation, particularly for uric acid, calcium phosphate, and calcium oxalate stones.
Low urine volume, high sodium intake, high animal protein consumption, and low calcium intake have all been identified as risk factors that can facilitate the formation of kidney stones. Sodium increases the excretion of calcium, while consuming high levels of animal protein can significantly increase uric acid excretion and decrease protective urinary citrate levels, thereby promoting stone growth. Conversely, adequate fluid intake dilutes urine and reduces the risk of kidney stones forming, while adequate calcium intake binds oxalate and prevents absorption.
High levels of oxalate and calcium combined with low urine volume facilitate the formation of calcium oxalate stones, while calcium phosphate stones can form when volume is low but calcium and urine pH are high. Uric acid stones can occur when volume and pH are low, but uric acid is high.
Urine studies have shown that after people adopt the carnivore diet, calcium, and uric acid levels often double, oxalate and sodium levels tend to increase, while citrate, which is protective, typically decreases. Additionally, the absence of fruits and vegetables eliminates alkalizing dietary components, further exacerbating stone risk.
Recent research also suggests that dietary fiber plays a role in reducing kidney stone risk, likely due to its effects on gut microbiota and urine pH. The absence of fiber in a carnivore diet could contribute to gut dysbiosis, which has been associated with an increased likelihood of nephrolithiasis.
Recommendations for Patients and Providers
To prevent kidney stones, patients should lower sodium intake by avoiding processed soups and meats and substituting salt with herbs. Reducing sodium is particularly important because high sodium intake drives calcium excretion, which increases the risk of calcium-based stones.
Non-dairy animal protein, particularly red meats, should be reduced, while fruits and vegetables such as citrus fruits, bell peppers, broccoli, and bananas should be increased. These foods provide essential citrate, which helps prevent calcium stone formation.
Raising dairy consumption can bind oxalate within the gastrointestinal tract, reducing oxalate absorption and decreasing the risk of calcium oxalate stones. For patients with persistent hypercalciuria, medications such as chlorthalidone may be prescribed to lower urinary calcium excretion.
Providers should use evidence from randomized controlled trials and high-quality research to guide their dietary advice. Social media and anecdotal claims should not replace clinically validated recommendations. If patients show interest in fad diets, clinicians can engage with them through motivational interviewing, asking about their goals and understanding their reasoning rather than outright dismissing their choices. The possible harms of fad diets should be emphasized, but physicians should also stay updated on research and guidelines and modify their advice accordingly.
Conclusions
The carnivore diet, which can lead to short-term weight loss, has gained popularity on social media. However, clinical urine studies show that following the carnivore diet increases multiple risk factors for kidney stone formation, including elevated calcium, uric acid, and oxalate levels, as well as reduced protective citrate levels. These findings highlight the importance of evidence-based dietary guidance rather than relying on anecdotal recommendations or social media trends.
The lack of long-term studies on the carnivore diet’s effects on kidney health underscores the need for further research. Physicians and dietitians should play an active role in educating patients about the risks of extreme diets and encouraging balanced, sustainable nutrition for kidney stone prevention.