Kidney stones may not be on your mind when beginning a weight-loss diet, but if you plan to follow a high-protein, low-carbohydrate diet plan, they should be. While many popular low-carb commercial diet plans encourage your body to shift into a fat-burning state called ketosis, the production of ketones that results can alter your urine chemistry and raise the risk of kidney stones.
Understanding the risks to your kidneys can help you decide whether the weight loss promises of a high-protein, low-carb diet are worth it.
What Are Kidney Stones?
Kidney stones develop when a hard mass of crystals develops in the urinary tract. Kidney stones are often extremely painful, especially when they pass through the thin ureter to exit the body.
There are a few different types of kidney stones, each made up of different materials. The cause of kidney stones can vary, but some people seem to be more prone to developing them than others, so there may be a hereditary component.
What Are Ketones?
Ketones are compounds formed by the breakdown of fat as the body shifts from burning carbohydrates to burning fat for fuel. During a high-protein, low-carbohydrate diet, ketones become the main source of energy in the body.
After a few days or weeks on this type of diet, the brain begins to use ketones as fuel instead of glucose. However, when too many ketones build up in the bloodstream, the pH of the urine changes from neutral to slightly acidic, which can put stress on the kidneys and potentially raise the risk of developing kidney stones.
High-Protein Diet Effect on Kidneys
A 2002 study published in the American Journal of Kidney Diseases found that a high-protein, low-carbohydrate diet raised the acidity of the blood over a six-week period, a condition known to contribute to kidney stones — specifically, uric acid stones. The study found up to a 90-percent increase in acid levels in the bloodstream.
In addition to the higher acid levels, the concentration of urinary citrate, a compound that inhibits the growth of kidney stones, was 25 percent lower. People consuming a diet high in protein may also become dehydrated, which concentrates the urine and may contribute to kidney stone development.
Individuals who are on a normal diet and develop kidney stones are frequently advised to reduce their intake of meat, poultry and fish protein in an attempt to prevent future kidney stones.
In addition to the higher risk of kidney stones, the study published in the American Journal of Kidney Diseases also found indicators that a high-protein, low-carbohydrate diet may increase the risk of bone loss. When dieters enter the state of ketosis induced by a high-protein diet, they may also experience other health problems, such as dehydration, dizziness, weakness or irritability.
- National Kidney and Urologic Diseases Information Clearinghouse; Kidney Stones in Adults; Oct. 2007
- NutraIngredients.com; High-Protein Diets Increase Risks of Kidney Stones, Bone Loss; Aug. 5, 2002
- "American Journal of Kidney Diseases"; Effect of Low-Carbohydrate High-Protein Diets on Acid-Base Balance, Stone-Forming Propensity, and Calcium Metabolism; S.T. Reddy, et al.; Aug. 2002
- MedlinePlus; Kidney Stones; updated by Louis S. Liou, M.D., Ph.D.; Jan. 14, 2009